bluuebunny/crossref_metadata_2025 huggingface dataset:
Induced resistance in rice against insects
Authors: Karban R. , Chen Y.
Published: July 2007

Vaccinations are the mainstay of western preventive medicine, and they have been used to protect some crops against disease and insect pests. We consider rice as a model for protection using induced resistance since it is one of the most important staple crops and there have been significant new developments in: cross-resistance among rice insects, chemical pathways involved in induced resistance, sequencing the rice genome and expression of genes conferring resistance against rice insect pests. Insect attack has been found to cause lesions that kill planthopper eggs and early stages of gall midges. Damaged plants released volatiles that made them less likely to be chosen by planthoppers and more attractive to parasitoids. Chemical elicitors have been developed for dicotyledonous plants and these can induce resistance in rice, although rice does not fit models developed to explain signalling in dicots. For example, salicylic acid did not increase in rice after infection by pathogens and did not appear to be the mobile signal for induced resistance against pathogens although it was involved in induced responses to phloem-feeding insects. Jasmonic acid acted as a signal in some induced responses to pathogens as well as chewing insects. Many of the genes associated with induced resistance in rice have recently been mapped, and techniques are being developed to incorporate them into the genome of cultivated varieties. Attempts to control insect pests of rice will affect interactions with pathogens, predators and parasites, and other organisms in this agroecosystem.
Impact of an exotic parasitoid onPlutella xylostella(Lepidoptera: Plutellidae) population dynamics, damage and indigenous natural enemies in Kenya
Authors: Löhr B. , Gathu R. , Kariuki C. , Obiero J. , Gichini G.
Published: July 2007

Diadegma semiclausum(Hellén) (Hymenoptera: lchneumonidae), an exotic diamondback moth parasitoid, was released in two pilot areas (Werugha in Coast Region and Tharuni in Central Province) in Kenya. Fifteen month before release, observations on the diamondback moth,Plutella xylostella(Linnaeus), and local natural enemy population dynamics and pest damage were initiated in both areas and continued for three years after release. TheP. xylostellapopulation was bimodal with higher records during dry seasons. At Werugha, the peak population ofP. xylostellawas 16.8 per plant (October 2001); at Tharuni it was 12.8 (February 2002). Populations at Werugha declined from three months after release and decreased from 5.4 per plant (before release) to 0.8 (year 3 after release). Concurrently, average damage (1.9 to 1.5) (on a 0–5 scale), proportion of attacked plants (72 to 31%) and proportion of plants in damage group >2 (plants with head damage) decreased (21.4 to 5.3%), while total parasitism increased from 14.4 (before) to 52.5% (year 3 after release, 90% due toD. semiclausum). At Tharuni,D. semiclausumwas only recovered 3 months after release. Average populations ofP. xylostelladeclined from 5.9 per plant (before release) to 2.4 (year 3 after release) and damage scores from 2.3 to 1.7. The proportion of plants in damage group >2 declined from 39.7 to 4.5% while overall parasitism increased from 4.2 to 40.6% (98.3% byD. semiclausum). Four species of indigenous parasitoids (Diadegma mollipla(Holmgren),Oomyzus sokolowskii(Kurdjumov), Apantelessp. andItoplectissp., all primary parasitoids) were almost completely displaced byD. semiclausum. Possible reasons for the different parasitoid development between the two release areas and the displacement of the indigenous species are discussed.
Chemosterilants as control agents of Ceratitis capitata (Diptera: Tephritidae) in field trials
Authors: Navarro-Llopis V. , Sanchis J. , Primo-Millo J. , Primo-Yúfera E.
Published: July 2007

Lufenuron is a chitin synthesis inhibitor, which is able to impede Mediterranean fruit fly, Ceratitis capitata (Wiedemann), reproduction. In laboratory trials, following ingestion of lufenuron, the eggs laid by female Ceratitis capitata were prevented from hatching. In field trials in Valencia, Spain, lufenuron showed its effectiveness by reducing C. capitata wild populations and its continuous application to several generations of fruit fly resulted in increased pest control. This field trial was conducted in an isolated valley some 80 ha in size, over a continuous four-year period. In order to maintain the sterilizing effect in the field throughout the whole year, a new lufenuron bait gel was developed. This bait gel was introduced in to delta traps suspended in trees at a density of 24 traps ha−1, and these traps were replaced once a year during the field trial. Monitoring of the adult C. capitata population was conducted to assess the effects of the chemosterilant treatment. In the first year of treatment with sterilizing traps, a reduction of the C. capitata population was observed, indicating that the traps reduce the population right from the first generation. In the second, third and fourth years, a continuous and progressive reduction of the adult Mediterranean fruit fly population was observed. Therefore, the successive application of chemosterilization treatment has a cumulative effect on reducing the fly population year after year. Aerial treatment using malathion does not produce this cumulative effect, and consequently every year it is necessary to start again with the same number of flies as the year before. The possibility of using the chemosterilant method alone or combined with the sterile insect technique is discussed.
Biotype-dependent secondary symbiont communities in sympatric populations of Bemisia tabaci
Authors: Chiel E. , Gottlieb Y. , Zchori-Fein E. , Mozes-Daube N. , Katzir N. , Inbar M. , Ghanim M.
Published: July 2007

The sweet potato whitefly, Bemisia tabaci, harbors Portiera aleyrodidarum, an obligatory symbiotic bacterium, as well as several secondary symbionts including Rickettsia, Hamiltonella, Wolbachia, Arsenophonus, Cardinium and Fritschea, the function of which is unknown. Bemisia tabaci is a species complex composed of numerous biotypes, which may differ from each other both genetically and biologically. Only the B and Q biotypes have been reported from Israel. Secondary symbiont infection frequencies of Israeli laboratory and field populations of B. tabaci from various host plants were determined by PCR, in order to test for correlation between bacterial composition to biotype and host plant. Hamiltonella was detected only in populations of the B biotype, while Wolbachia and Arsenophonus were found only in the Q biotype (33% and 87% infection, respectively). Rickettsia was abundant in both biotypes. Cardinium and Fritschea were not found in any of the populations. No differences in secondary symbionts were found among host plants within the B biotype; but within the Q biotype, all whiteflies collected from sage harboured both Rickettsia and Arsenophonus, an infection frequency which was significantly higher than those found in association with all other host plants. The association found between whitefly biotypes and secondary symbionts suggests a possible contribution of these bacteria to host characteristics such as insecticide resistance, host range, virus transmission and speciation.
Initial-boundary value problems for linear PDEs with variable coefficients
Authors: TREHARNE P. A. , FOKAS A. S.
Published: July 2007

A new approach for studying initial-boundary value problems for linear partial differential equations (PDEs) with variable coefficients was introduced recently by the second author, and was applied to PDEs involving second order derivatives. Here, we extend this approach further to solve an initial-boundary value problem for a third-order evolution PDE with a space-dependent coefficient. The analysis is presented in such a way that it can be applied to PDEs with higher derivatives, and thus provides a method for solving initial-boundary value problems for a certain class of linear evolution equations with variable coefficients of arbitrary order.
Quasiconformal homogeneity of hyperbolic surfaces with fixed-point full automorphisms
Authors: BONFERT–TAYLOR PETRA , BRIDGEMAN MARTIN , CANARY RICHARD D. , TAYLOR EDWARD C.
Published: July 2007

We show that any closed hyperbolic surface admitting a conformal automorphism with “many” fixed points is uniformly quasiconformally homogeneous, with constant uniformly bounded away from 1. In particular, there is a uniform lower bound on the quasiconformal homogeneity constant for all hyperelliptic surfaces. In addition, we introduce more restrictive notions of quasiconformal homogeneity and bound the associated quasiconformal homogeneity constants uniformly away from 1 for all hyperbolic surfaces.
A Denjoy–Wolff theorem for Hilbert metric nonexpansive maps on polyhedral domains
Authors: LINS BRIAN
Published: July 2007

For a polyhedral domain$\Sigma \subset \mathbb{R}^n$, and a Hilbert metric nonexpansive mapT:Σ→Σ which does not have a fixed point in Σ, we prove that the omega limit set ω(x;T) of any pointx∈ Σ is contained in a convex subset of the boundary ∂Σ. We also identify a class of order-preserving homogeneous of degree one maps on the interior of the standard cone$\mathbb{R}^n_+$which demonstrate that there are Hilbert metric nonexpansive maps on an open simplex with omega limit sets that can contain any convex subset of the boundary.
On the actions of a locally compact group on some of its semigroup compactifications
Authors: FILALI M.
Published: July 2007

LetGbe a locally compact group and$\mathcal{U}G$be its largest semigroup compactification. Thensx≠xin$\mathcal{U}G$wheneversis an element inGother thane. This result was proved by Ellis in 1960 for the caseGdiscrete (and so$\mathcal{U}G$is the Stone–Čech compactification βGofG), and by Veech in 1977 for any locally compact group. We study this property in theWAP– compactification$\mathcal{W}G$ofG; and in$\mathcal{U}G$, we look at the situation whenxs≠x. The points are separated by some weakly almost periodic functions which we are able to construct on a class of locally compact groups, which includes the so-called E-groups introduced by C. Chou and which is much larger than the class of SIN groups. The other consequences deduced with these functions are: a generalization of some theorems on the regularity of$\mathcal{W}G$due to Ruppert and Bouziad, an analogue in$\mathcal{W}G$of the “local structure theorem” proved by J. Pym in$\mathcal{U}G$, and an improvement of some earlier results proved by the author and J. Baker on$\mathcal{W}G$.
Reversible maps in the group of quaternionic Möbius transformations
Authors: LÁVIČKA ROMAN , O'FARRELL ANTHONY G. , SHORT IAN
Published: July 2007

The reversible elements of a group are those elements that are conjugate to their own inverse. A reversible element is said to be reversible by an involution if it is conjugate to its own inverse by an involution. In this paper, we classify the reversible elements and the elements reversible by involutions in the group of quaternionic Möbius transformations.
Spectral gaps of the Schrödinger operators with periodic δ′-interactions and Diophantine approximations
Authors: YOSHITOMI KAZUSHI
Published: July 2007

We study the spectral gaps of the Schrödinger operatorwhere κ∈(0,2π) and$\beta_{1},\beta_{2}\in{\mathbb R}\setminus\{0\}$are parameters. Let τ=2π−κ. Suppose that the ratio κ0:=τ/κ is irrational. We denote thejth gap of the spectrum ofHbyGj, its length by |Gj|. We obtain a relationship between the asymptotic behaviour of |Gj| asj→∞ and the Diophantine properties of κ0. In particular, we show that if β1+β2=0, thenwhereM(κ0) stands for the Markov constant of κ0.
The lattice of balanced equivalence relations of a coupled cell network
Authors: STEWART IAN
Published: July 2007

A coupled cell system is a collection of dynamical systems, or ‘cells’, that are coupled together. The associated coupled cell network is a labelled directed graph that indicates how the cells are coupled, and which cells are equivalent. Golubitsky, Stewart, Pivato and Török have presented a framework for coupled cell systems that permits a classification of robust synchrony in terms of the concept of a ‘balanced equivalence relation’, which depends solely on the network architecture. In their approach the network is assumed to be finite. We prove that the set of all balanced equivalence relations on a network forms a lattice, in the sense of a partially ordered set in which any two elements have a meet and a join. The partial order is defined by refinement. Some aspects of the theory make use of infinite networks, so we work in the category of networks of ‘finite type’, a class that includes all locally finite networks. This context requires some modifications to the standard framework. As partial compensation, the lattice of balanced equivalence relations can then be proved complete. However, the intersection of two balanced equivalence relations need not be balanced, as we show by a simple example, so this lattice is not a sublattice of the lattice of all equivalence relations with its usual operations of meet and join. We discuss the structure of this lattice and computational issues associated with it. In particular, we describe how to determine whether the lattice contains more than the equality relation. As an example, we derive the form of the lattice for a linear chain of identical cells with feedback.
Controls on black carbon storage in soils
Authors: Czimczik Claudia I. , Masiello Caroline A.
Published: July 2007

Fire‐derived black carbon (BC: charcoal and soot) has been thought to be a passive player in soils, contributing to the refractory soil organic carbon (SOC) pool, but playing no role in pedogenesis and regional short‐term carbon cycling. This model, however, is at odds with recent results on the role of charcoal in soil fertility and its detection in the dissolved organic carbon (DOC) pool. For example, if BC simply accumulated passively in soils, its pattern of accumulation should match a simple model correlating fire frequency to BC storage. Instead, soil type, climate, biota, and land use practices all appear to play roles in controlling whether BC accumulates or is lost from soils. We summarize current knowledge of BC‐soil interactions and construct a new paradigm describing the controls on BC storage in soils. We reconcile the refractory‐labile BC paradox by proposing a model where BC storage is controlled by (1) fire frequency, (2) ecosystem presence or absence of aromatic precursor carbon and appropriate combustion conditions, (3) biological or physical mixing to remove BC from the soil surface, where it is vulnerable to combustion in future fires, (4) the presence or absence of soil mineral fractions able to sorb BC into the long‐term stable carbon pool, and (5) the presence of microbial communities capable of degrading aromatic carbon. We also recognize that soil BC/SOC ratios are strongly influenced by land‐use practices and add (6) human activities as a final control.
Deformation method for electromagnetic magnetospheric fields: 2. Application to the Earth's magnetosphere
Authors: Toivanen P. K.
Published: July 2007

A new magnetospheric magnetic field model given globally in terms of the Euler potentials is constructed. It complements the preexisting model magnetic fields with a possibility of straightforward inclusion of electric fields, especially those arising from temporal variations of the model magnetic field. The model is based on the deformation method, and a short review of the method is given. The model is parameterized with geometrical input parameters, for example such as location of the subsolar point, colatitudes of the cusp and nightside poleward boundary of the auroral oval, and radius of the tail. These primary parameters can be used to vary the overall geometry of the model in response to geomagnetic conditions. In addition, several secondary parameters can be varied to fit the model to the geometric constraints set by the primary parameters. The model is constructed by applying five consecutive deformations to an initial magnetic field configuration of a dipole field. Such a model construction is convenient if local perturbations to the model are considered: Perturbations can be first introduced as deformations to the dipole field using its fairly simple analytic nature and then embedded in a realistic field configuration by applying the presented deformations to the perturbed dipole field. The resulting magnetic field model compares well to a preexisting empirical model, and in addition, the current systems of the model are realistic including the major magnetospheric current systems: the dayside magnetopause current, ring current, and the cross‐tail current.
Comparison of COSMIC ionospheric measurements with ground‐based observations and model predictions: Preliminary results
Authors: Lei Jiuhou , Syndergaard Stig , Burns Alan G. , Solomon Stanley C. , Wang Wenbin , Zeng Zhen , Roble Raymond G. , Wu Qian , Kuo Ying‐Hwa , Holt John M. , Zhang Shun‐Rong , Hysell David L. , Rodrigues Fabiano S. , Lin Chien H.
Published: July 2007

Electron densities retrieved from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation (RO) measurements are compared with those measured by incoherent scatter radars (ISR) and ionosondes in this paper. These results show that electron density profiles retrieved from COSMIC RO data are in agreement with the ISR and ionosonde measurements. The ionospheric characteristics (NmF2 and hmF2) derived from the COSMIC satellites are also compared with those calculated by the latest International Reference Ionosphere model (IRI‐2001) and the National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (NCAR‐TIEGCM). The comparison of the magnitude of the COSMIC NmF2 data with those calculated by the IRI model and the TIEGCM is good. However, features such as the north‐south asymmetry and longitudinal variation of the equatorial anomaly that are seen in the COSMIC data and the TIEGCM simulations are not fully present in the IRI model. On the other hand, the TIEGCM produces a stronger winter anomaly than that seen in either the COSMIC data or the IRI model.
Turbulent dissipation in a near‐field river plume: A comparison of control volume and microstructure observations with a numerical model
Authors: MacDonald Daniel G. , Goodman Louis , Hetland Robert D.
Published: July 2007

Data collected from the near‐field region (first several kilometers) of the Merrimack River plume are analyzed to provide estimates of turbulent kinetic energy (TKE) dissipation rates. Measurement techniques included a control volume method incorporating density and velocity survey data, and direct dissipation rate measurements by turbulence sensors mounted on an autonomous underwater vehicle (AUV). These two distinct observational approaches are compared with TKE dissipation rates derived from a highly resolved three‐dimensional numerical model. In general, there is good agreement between the three estimates of dissipation rate. Differences occurred in two regions: (1) at the base of the plume, where plume density increased, and (2) in the very near field of the plume, which is characterized by rapid acceleration and strong shoaling. Results suggest that there is a feedback between the turbulence and the plume evolution with the result that the spreading rate of the plume is constrained. A scaling parameterization, relating turbulent dissipation rate to plume density and velocity, is also examined. Immediately seaward of the front this parameterization appears to be consistent with observed rates of dissipation, but progressing seaward, a modification to the parameterization may be necessary to account for plume spreading and deepening.
A new climatology for atmospheric correction based on the aerosol inherent optical properties
Authors: Zagolski Francis , Santer Richard , Aznay Ouahid
Published: July 2007

In the aerosol remote sensing algorithms over ocean, the aerosol models are deduced from the spectral dependence of the path radiances in the near‐infrared region. In the classical scheme of atmospheric corrections, the key point is the derivation of atmospheric signals in the visible part of the solar spectrum using these aerosol models. The aerosol climatology generally includes the standard aerosol models. Nevertheless, the latter may not be representative enough of the variety of aerosols encountered over coastal areas. One way to extend this climatology is to generate additional aerosol models. The latters will be described by their micro‐physical properties and their inherent optical properties (IOPs) can then be computed with the Mie's theory. Coastal and inland stations of CIMEL sun‐photometers from the AERONET (AErosol RObotic NETwork) offer an extensive and representative data set of aerosol characteristics (i.e., the apparent optical properties from which can be derived the IOPs) in the marine environment through solar extinction and sky radiance measurements. An iterative method, developed at the ≪ Laboratoire Interdisciplinaire des Sciences de l'Environnement ≫ (LISE, Wimereux‐France), allows to extract the aerosol phase function from these ground‐based measurements. CIMEL data, collected over 25 stations during several years, were processed to build‐up a database with more than 7000 sequences including single scattering albedos and phase functions at two wavelengths (675 nm and 870 nm). Statistical methods have been applied on this data set to discard the wrong sequences and to suggest a classification in aerosol models through their IOPs.
Observation of ambient aerosol particle growth due to in‐cloud processes within boundary layers
Authors: Wang Jian , Daum Peter H. , Kleinman Lawrence I. , Lee Yin‐Nan , Schwartz Stephen E. , Springston Stephen R. , Jonsson Haflidi , Covert David , Elleman Robert
Published: July 2007

Aerosol microphysical and optical properties were measured on board the CIRPAS Twin Otter aircraft during 16 flights at the Southern Great Plain (SGP) site in northern central Oklahoma as part of the Aerosol Intensive Operation period in May 2003. Within well‐mixed boundary layers on four cloudy days, vertical profiles measured on board the Twin Otter show that dry aerosol size, volume concentration, and scattering coefficients all increased with increasing altitude, whereas the total number concentration remained essentially constant. A one‐dimensional model, which uses simultaneous meteorological measurements as inputs, shows that the observed increase in aerosol volume concentration with increasing altitude is consistent with in‐cloud sulfate production at the top of the boundary layer. The sulfate production rate was sufficiently fast to overcome the homogenization resulting from turbulent mixing. In contrast, on cloud‐free days, measurements on a second aircraft show nearly uniform aerosol volume concentrations within well‐mixed boundary layers. The observed vertical gradients in aerosol volume concentration suggest that even within well‐mixed boundary layers, surface measurements may not be representative of aerosols properties (e.g., loading and scattering coefficients, etc.) at elevated altitudes, especially when SO2 concentration and cloud coverage are high.
Modeling and interpretation of stable carbon isotope ratios of ethane in global chemical transport models
Authors: Stein Olaf , Rudolph Jochen
Published: July 2007

Model calculations with two global 3D‐CTMs (GISS and MOZART‐2) in which we introduced ethane stable carbon isotopic ratios were performed. In both models, emission inventories based on the EDGAR database are used for VOC emissions. We considered source specific isotope fractionations and included global emissions from C3 and C4 plants which differ significantly in isotope ratio. Comparison of the model results with observation strongly indicates that the EDGAR emission inventory underestimates global ethane emissions by a factor of approximately 1.5. On the basis of the latitude‐dependent differences between model predictions and the atmospheric observations of ethane reported by Rudolph (1995), estimates of magnitude and latitude range of sources missing in current emission inventories are made. However, the concentration data alone provide only limited constraints on the geographical distribution and only indirect information about the type of the missing sources. Isotope ratio studies can be very valuable to obtain additional insight. To study the dependence between the geographical distribution of the emissions and atmospheric ethane concentrations and isotope ratios, MOZART‐2 model calculations were made where all emissions are concentrated in latitude bands as well as in specified regions. Two regimes can be distinguished on a global scale: In the source latitude band, dilution with background air explains most of the calculated concentration variation, while at latitudes farther away from the sources, chemical loss is the dominating process.
Impact of sea breeze air masses laden with ozone on inland surface ozone concentrations: A case study of the northern coast of Taiwan
Authors: Lin Ching‐Ho , Lai Chin‐Hsing , Wu Yee‐Lin , Lin Po‐Hsiung , Lai Hsin‐Chih
Published: July 2007

This work examines how ozone‐laden sea breeze air masses contribute to inland surface ozone concentrations. The vertical distributions of ozone in sea breeze air masses and the characteristics of sea breezes are investigated using tethered ozonesondes and meteorological radiosondes, respectively, at a measurement site near the northern coast of Taiwan during 24–30 August 2003. The investigations reveal that, initially, sea breeze air masses are stable with relatively high concentrations of ozone distributed in the upper portions of the air masses. Elevated ozone layers with concentrations of 60–100 ppb were frequently observed at 500–1600 m. The growth of a thermal internal boundary layer (TIBL) inland that can bring ozone‐rich air aloft in a sea breeze air mass into the growing TIBL subsequently increases the surface ozone concentrations farther inland. Accordingly, the surface ozone concentrations increase with distance inland, regardless of the photochemical production of ozone inland. A new conceptual model was presented to depict this pollution feature. According to a simple Lagrangian analysis, ozone‐rich sea breeze air masses under the observed conditions generated a difference of as much as a 30 ppb between the surface ozone concentration at a near‐coast location and that at a far inland location. TIBL development at a near‐coast area can protect the area from fumigation of elevated ozone layers because the depth of the TIBL is limited there, such that the ozone in the elevated ozone layers cannot be brought to the ground.
Radiative transfer mixing models of meteoritic assemblages
Authors: Lawrence Samuel J. , Lucey Paul G.
Published: July 2007

A spectral mixing model for the expected conditions on asteroid surfaces based on Hapke's radiative transfer theory for intimate mixtures is presented. This model calculates the visible/near‐infrared reflectance spectrum of an intimate mixture incorporating the modal mineralogy, the mineral chemistry, the particle size, and the degree of space weathering as factors, and includes an improved treatment for the spectral effects of coarse‐grained Fe,Ni‐metal. This model can reproduce the spectra of geologically plausible mixtures of silicate components and meteorites with known mineral abundances, chemistry, and particle sizes. We compare the model spectral effects of the coarse‐grained Fe,Ni‐metal naturally present on asteroid surfaces to the spectral effects of submicroscopic iron produced by lunar‐style space weathering. The model spectral effects of large asteroid surface concentrations of coarse‐grained Fe,Ni‐metal are similar to the spectral effects of SMFe in some cases. We model the composition of asteroid 4 Vesta and find it to be consistent with a minimally space‐weathered eucritic composition. Finally, we predict the spectral properties of some example of ordinary chondrite parent bodies. When modeled with particle sizes matching the optically dominant particle size of the lunar surface and minimal abundances of SMFe, these model ordinary chondrite parent bodies plot outside the S(IV) asteroid field on a Band area ratio versus Band I center plot. We find that a combination of larger particle sizes and increased SMFe abundances is the most effective way to move these models into the S(IV) field.
Melt distribution beneath a young continental rift: The Taupo Volcanic Zone, New Zealand
Authors: Heise Wiebke , Bibby Hugh M. , Caldwell T. Grant , Bannister Stephen C. , Ogawa Yasuo , Takakura Shinichi , Uchida Toshihiro
Published: July 2007

Taupo Volcanic Zone (TVZ) is a zone of intense volcanism and rifting associated with the subduction of the Pacific Plate beneath the continental crust of New Zealand's North Island. An image of the conductivity structure beneath the central part of the TVZ has been constructed using 2‐D inverse modeling of magnetotelluric data. A rapid increase in conductivity at a depth of 10 km beneath the TVZ, ∼3 km beneath the base of the seismogenic zone but well above the base of the quartzo‐feldspathic crust (∼16 km), is interpreted to mark the presence of an interconnected melt fraction (<4%) within the lower crust. Beneath the quartzo‐feldspathic crust the model shows a zone of increased conductivity on the eastern side of the TVZ consistent with an increased concentration of melt. At deeper levels the Pacific Plate is resistive compared with the overlying mantle.
Broadening of solar wind strahl pitch‐angles by the electron/electron instability: Particle‐in‐cell simulations
Authors: Gary S. Peter , Saito Shinji
Published: July 2007

Solar wind electrons in the suprathermal energy range from about 70 eV to greater than 1 keV usually are observed as two distinct, relatively tenuous components: an approximately isotropic halo and a strongly anisotropic “strahl” directed along the magnetic field. This manuscript describes a two‐dimensional electromagnetic particle‐in‐cell simulation in a magnetized, homogeneous, collisionless plasma with such a two‐component representation of suprathermal electrons. In this computation the electrostatic electron/electron instability is driven by a strahl with a large average speed along the background magnetic field Bo. The simulation demonstrates that this instability leads to substantial strahl velocity scattering perpendicular to Bo. The most important result here is that, for strahl speeds large compared to the halo thermal speed, after instability saturation the width of the electron pitch‐angle distribution exhibits a maximum as a function of electron energy.
Information content of near‐infrared spaceborne multiangular polarization measurements for aerosol retrievals
Authors: Lebsock Matthew D. , L'Ecuyer Tristan S. , Stephens Graeme L.
Published: July 2007

The information content of near‐infrared spectral multiangular polarization measurements, utilized in the POLDER operational aerosol algorithm, for retrieving aerosol microphysical and optical properties is assessed. It is found that spectral measurements contain just one unique piece of microphysical information, while multiangular measurements add a second and polarization observations permit the constraint of a third microphysical parameter. In addition, it is demonstrated that the relationship between the aerosol single scattering properties and the aerosol microphysical parameters is nonunique. The implications of these findings for aerosol microphysical retrievals are demonstrated through the development of a retrieval for the aerosol optical depth, the index of refraction and a parameter describing the ratio of the number concentration of accumulation mode aerosols to those in the coarse mode. Application of the technique centers on the explicit weighting of individual measurements by rigorous estimates of their uncertainties offering the benefit of a realistic, dynamic retrieval error estimate. The aerosol optical depth, refractive index and number concentration ratio can respectively be estimated to within 15%, 5% and one order of magnitude over oceans. Error estimates are shown to increase by 50% over a mixed forest land surface type. The results further highlight a possible limitation of the measurements at low optical depths below 0.1 where the retrieval errors approach 100% for the optical depth and index of refraction and several orders of magnitude for the number concentration ratio.
Normal levels of Rac1 are important for dendritic but not axonal development in hippocampal neurons
Authors: Gualdoni Sara , Albertinazzi Chiara , Corbetta Sara , Valtorta Flavia , de Curtis Ivan
Published: July 2007

Background information. Rho family GTPases are required for cytoskeletal reorganization and are considered important for the maturation of neurons. Among these proteins, Rac1 is known to play a crucial role in the regulation of actin dynamics, and a number of studies indicate the involvement of this protein in different steps of vertebrate neuronal maturation. There are two distinct Rac proteins expressed in neurons, namely the ubiquitous Rac1 and the neuron‐specific Rac3. The specific functions of each of these GTPases during early neuronal development are largely unknown.

Results. The combination of the knockout of Rac3 with Rac1 down‐regulation by siRNA (small interfering RNA) has been used to show that down‐regulation of Rac1 affects dendritic development in mouse hippocampal neurons, without affecting axons. F‐actin levels are strongly decreased in neuronal growth cones following down‐regulation of Rac1, and time‐lapse analysis indicated that the reduction of Rac1 levels decreases growth‐cone dynamics.

Conclusions. These results show that normal levels of endogenous Rac1 activity are critical for early dendritic development, whereas dendritic outgrowth is not affected in hippocampal neurons from Rac3‐null mice. On the other hand, early axonal development appears normal after Rac1 down‐regulation. Our findings also suggest that the initial establishment of neuronal polarity is not affected by Rac1 down‐regulation.
‘Should I stay or should I go?’: myosin V function in organelle trafficking
Authors: Desnos Claire , Huet Sébastien , Darchen François
Published: July 2007

Actin‐ and microtubule‐based motors can propel different cargos along filaments. Within cells, they control the distribution of membrane‐bound compartments by performing complementary tasks. Organelles make long journeys along microtubules, with class V myosins ensuring their capture and their dispersal in actin‐rich regions. Myosin Va is recruited on to diverse organelles, such as melanosomes and secretory vesicles, by a mechanism involving Rab GTPases. The role of myosin Va in the recruitment of secretory vesicles at the plasma membrane reveals that the cortical actin network cannot merely be seen as a physical barrier hindering vesicle access to release sites. In neurons, myosin Va controls the targeting of IP3 (inositol 1,4,5‐trisphosphate)‐sensitive Ca2+ stores to dendritic spines and the transport of mRNAs. These defects probably account for the severe neurological symptoms observed in Griscelli syndrome due to mutations in the MYO5A gene.
A2breceptor mediates adenosine inhibition of taurine efflux from pituicytes
Authors: Pierson Patricia M. , Peteri‐Brunbäck Brigitta , Pisani Didier F. , Abbracchio Maria Pia , Mienville Jean‐Marc , Rosso Lia
Published: July 2007

Background information. Recent work suggests that part of the control of vasopressin output is mediated by taurine released from pituicytes, the astroglial cells of the neurohypophysis. Taurine release, in turn, is stimulated by hypotonic conditions and by vasopressin itself. As adenosine is generated from ATP co‐released with vasopressin, it appeared important to study its effects on taurine efflux from pituicytes.

Results. We measured radioactive efflux from cultured pituicytes and whole neurohypophyses pre‐loaded with [3H]taurine. Cultured pituicytes were also used to study adenosine‐receptor mRNA expression. Taurine efflux elicited by hypotonic shocks is ∼30–50% smaller in the presence of 10 μM adenosine or 1 μM NECA (5′‐N‐ethylcarboxamidoadenosine). Both compounds also inhibited basal efflux in a manner that was not immediately reversible. Agonists of the adenosine A1‐, A2a‐ or A3‐receptor subtypes have no relevant effect on basal taurine release, and the A1‐receptor antagonist DPCPX (8‐cyclopentyl‐1,3‐dipropylxanthine) has no effect on the inhibition of release by NECA. In turn, the A2b‐receptor antagonists MRS 1706 {N‐(4‐acetylphenyl)‐2‐[4‐(2,3,6,7‐tetrahydro‐2,6‐dioxo‐1,3‐dipropyl‐1H‐purin‐8‐yl)phenoxy]acetamide} or alloxazine partially reverse the inhibition of basal or hypotonicity‐evoked efflux by NECA. Both A1‐ and A2b‐receptor mRNAs are expressed in pituicytes, which is consistent with an A1‐receptor‐mediated effect on cell morphology and an A2b‐receptor‐mediated effect on taurine release. Forskolin and dibutyryl cAMP mimic the inhibitory effects of purinergics on basal taurine efflux, and the adenylate cyclase inhibitor DDA (2′,5′‐dideoxyadenosine) partially reverses the inhibition of the hypotonic response by NECA.

Conclusions. Our results suggest that purinergic inhibition of taurine efflux from pituicytes operates through A2breceptors coupled to intracellular cAMP increase. They point to a possible modulation of neurohypophysial hormone output by endogenous adenosine released in either physiological or pathological situations.
Factors controlling matrix turnover in health and disease
Authors: Buttle D.J.
Published: July 2007

The impact of changes in matrix turnover on disease processes is gradually becoming more widely understood and appreciated. Similarly, the importance of interactions between the cellular and acellular components of any given tissue is finally being realized. An unhealthy cell does not make a healthy matrix; likewise an unhealthy matrix often leads to the demise of the cells within it, or at the very least to major changes in cell phenotype. We can therefore no longer investigate these two components in isolation, because the matrix so often contributes to cellular signalling pathways, and these in turn can lead to changes in matrix turnover. This is a long way from the traditional view of the role of the extracellular matrix, or ‘ground substance’, in filling the spaces between the cells and providing physical support for them. Just over 100 delegates assembled at Sheffield Hallam University for the Joint BSMB (British Society for Matrix Biology)/Biochemical Society Focused Meeting on Matrix Turnover: Mechanisms and Common Denominators on 2–3 April 2007. The stated aim of the meeting was to aid and encourage interactions between scientists working in various areas of matrix biology, and to this end there were sessions on intervertebral disc, turnover in the CNS (central nervous system), fibroses and tumour–stroma interactions, as well as a session covering general topics. The involvement of both the BSMB and Biochemical Society membership increased the potential for interactions between scientists and hopefully increased the value of the meeting for all the delegates. This issue of Biochemical Society Transactions contains papers written by those who gave oral presentations at the meeting. I think it is fair to conclude from their talks and the papers presented here that the ‘common denominators’ involved in matrix turnover include cytokine and growth factor signalling pathways that control the rates of matrix synthesis and breakdown, and which, in many disease processes, lead to an uncoupling of synthesis and breakdown and thereby the loss of homoeostasis. Evidently, the make-up of the matrix surrounding cells profoundly affects cell phenotype and behaviour through various signalling pathways. Numerous environmental stimuli may trigger these events, and a host of genes are undoubtedly involved in generating predisposing genotypes. Such factors appear to be common to many diseases involving matrix turnover.
Three-dimensional extracellular matrix culture models of EGFR signalling and drug response
Authors: Kenny P.A.
Published: July 2007

Three-dimensional extracellular matrix culture, on substrata such as Matrigel, restores many aspects of the differentiated state to non-malignant cells from a variety of tissues. We have adapted these techniques to study EGFR (epidermal growth factor receptor) signalling and drug response in breast cancer cell lines. EGFR-dependent breast cancer cell lines undergo a striking reversion of the malignant phenotype upon treatment with inhibitors targeting the receptor, or downstream signalling intermediates such as mitogen-activated protein kinase and PI3K (phosphoinositide 3-kinase). Using this approach, we have recently reported that EGFR signalling in breast cancer can be effectively inhibited by blocking the activity of a key protease, TACE [TNFα (tumour necrosis factor α)-converting enzyme], which regulates the bioavailability of EGFR ligands. These results suggest a new way to target EGFR signalling in tumours of the breast and other epithelial tissues and underline the value of three-dimensional extracellular matrix culture models for exploring cancer-relevant signalling processes ex vivo.
The molecular basis of inter-α-inhibitor heavy chain transfer on to hyaluronan
Authors: Milner C.M. , Tongsoongnoen W. , Rugg M.S. , Day A.J.
Published: July 2007

The inflammation-associated protein TSG-6 (the product of tumour necrosis factor-stimulated gene-6) can form covalent complexes with the heavy chains (HC1 and HC2) of IαI (inter-α-inhibitor); namely, TSG-6·HC1 and TSG-6·HC2, which act as intermediates in the covalent transfer of HCs on to the GAG (glycosaminoglycan) HA (hyaluronan). HC·HA, which is formed for example in the synovial fluids of arthritis patients, is more aggregated than unmodified HA and has altered mechanical and cell-binding properties. The expansion of the HA-rich cumulus ECM (extracellular matrix) during ovulation is critically dependent on the catalysis of HC·HA generation by TSG-6, with TSG-6−/− mice being female infertile because of failure of HA cross-linking. It has been shown recently that TSG-6-mediated HC·HA formation is essential for the formation of HA-rich pericellular matrix and for cell migration in a model of wound healing. In contrast, in this model, the formation of cell-associated HA cable-like structures, although requiring the transfer of HCs on to HA, might not involve TSG-6. TSG-6-mediated HC transfer involves two sequential transesterification processes, where HCs are transferred from the CS (chondroitin sulfate) of IαI first on to TSG-6 and then on to HA. TSG-6 is an essential co-factor and catalyst in this chain of events, with both TSG-6·HC formation and HC transfer being dependent on the presence of Mg2+ or Mn2+ ions.
Influence of the extracellular matrix on the frictional properties of tissue-engineered cartilage
Authors: Plainfossé M. , Hatton P.V. , Crawford A. , Jin Z.M. , Fisher J.
Published: July 2007

Low-friction surfaces are critical for efficient joint articulation. The tribological properties of articular cartilage have been studied extensively in native tissue and joints. Despite their importance, very few studies have examined the frictional properties of tissue-engineered cartilage. We have therefore reviewed the relationship between composition, structure and friction in tissue-engineered cartilage.
‘Rumours of my death may have been greatly exaggerated’: a brief review of cell death in human intervertebral disc disease and implications for cell transplantation therapy
Authors: Johnson W.E.B. , Roberts S.
Published: July 2007

The avascular nature of the human intervertebral disc is thought to reduce the ability of resident disc cells to maintain their extracellular matrix, rendering the tissue susceptible to degeneration. It has also been suggested that the lack of a blood supply may result in disc cell death via nutrient deprivation. Therefore transplanting new cells into the disc to promote tissue regeneration would be akin to ‘putting cells in a coffin’ and doomed to failure. This review considers the available evidence for cell death in the human intervertebral disc, describing briefly the methods used to assay such death, and concludes that further analysis is required to ascertain whether extensive cell death truly is a marked feature of human intervertebral discs and whether it bears any relationship to disc degeneration and hence regenerative strategies.
Matrix metalloproteinases: useful and deleterious
Authors: Ganea E. , Trifan M. , Laslo A.C. , Putina G. , Cristescu C.
Published: July 2007

MMPs (matrix metalloproteinases) are zinc-dependent endopeptidases that degrade both matrix and non-matrix proteins. They play an important role in morphogenesis, and in a wide range of processes including tissue repair and remodelling. Their abnormal expression contributes to pathological processes including arthritis, cancer, and cardiac and central nervous system diseases, which explains the large interest in finding specific MMP inhibitors for therapeutic use. In this review we describe the structural features of MMPs, with special emphasis on their interaction with specific inhibitors. The effect of new, hydroxamatebased inhibitors on MMP isolated from bovine brain is evaluated.
Brevican and phosphacan expression and localization following transient middle cerebral artery occlusion in the rat
Authors: Haddock G. , Cross A.K. , Allan S. , Sharrack B. , Callaghan J. , Bunning R.A.D. , Buttle D.J. , Woodroofe M.N.
Published: July 2007

The ECM (extracellular matrix) is a complex molecular framework that provides physical support to cells and tissues, while also providing signals for cell growth, migration, differentiation and survival. The ECM of the CNS (central nervous system) is unusual in that it is rich in CSPGs (chondroitin sulfate proteoglycans), hyaluronan and tenascins. The CSPGs are widely expressed throughout the developing and adult CNS and have a role in guiding or limiting neurite outgrowth and cell migration. Alterations in the synthesis or breakdown of the ECM may contribute to disease processes. Here, we examine changes in the brain-specific CSPGs, brevican and phosphacan, following transient middle cerebral artery occlusion, a model of stroke in the rat. We have investigated their expression at various time points as well as their spatial relationship with ADAMTS-4 (adisintegrin and metalloprotease with thrombospondin motifs 4). The co-localization of ADAMTS or its activity may indicate a functional role for this matrix–protease pair in degeneration/regeneration processes that occur in stroke.
Regulation of fibroblast migration by tenascin-C
Authors: Trebaul A. , Chan E.K. , Midwood K.S.
Published: July 2007

Synthesis of new tissue by fibroblasts is required for tissue rebuilding in response to injury. Fibroblast migration from surrounding healthy tissue into the fibrin–fibronectin provisional matrix deposited upon injury is a key rate-limiting step of this stage of tissue repair. These events must be tightly regulated. Excessive deposition of scar tissue is the major hallmark of fibrotic disease. Tenascin-C is an extracellular matrix glycoprotein that is transiently expressed upon tissue injury, where it is specifically localized to the wound edge, and persistently up-regulated in fibrotic disease. We have shown that full-length tenascin-C promotes fibroblast migration within fibrin–fibronectin matrices and we have mapped the domains within the molecule critical for enhancing migration. We also demonstrated that specific fragments of tenascin-C inhibit fibroblast migration. These results suggest that transient expression of tenascin-C at the wound boundary is key to tissue repair: its induction recruits fibroblasts into the wound and fragments resulting from its breakdown prevent excessive fibroblast infiltration. Our results demonstrate how fibroblast migration in three-dimensional provisional matrices may be differentially regulated by proteolysis of matrix molecules and could explain how persistent expression of tenascin-C contributes to the progression of fibrotic disease.