bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduction of atherosclerosis despite hypercholesterolemia in lyn‐deficient mice fed a high‐fat diet
Authors: Miki Shunji , Horikawa Keisuke , Nishizumi Hirofumi , Suemura Masaki , Sato Bunzo , Yamamoto Masahiro , Takatsu Kiyoshi , Yamamoto Tadashi , Miki Yoshitsugu
Published: March 2003

Oxidation and other modifications of serum low‐density lipoprotein (LDL) are associated with the development of atherosclerosis, and a scavenger receptor and CD40 signalling are also known to play important roles in the process. We previously showed that the Src family protein‐tyrosine kinase Lyn is physically and/or functionally associated with macrophage type‐I and type‐II class‐A scavenger receptors (MSR‐A) and CD40.

In this study, we addressed whether Lyn is involved in the build‐up of serum lipid levels and in atherosclerotic changes. When fed a normal diet, lyn‐deficient mice had serum lipid levels that were no different from those of wild‐type mice. By contrast, lyn‐deficient mice fed a high‐fat diet showed serum lipid levels that were much higher than those seen in wild‐type mice. Curiously, however, the lyn‐deficient mice fed either diet showed no increase in incidence of atherosclerotic lesions compared with wild‐type mice. This may be partly explained by our data showing suppression of proliferation of peritoneal macrophages in response to oxidized LDL in the absence of Lyn, and failure of stimulation of the CD40 pathway in lyn‐deficient macrophages to induce expression of monocytic chemoattractant protein‐1 (MCP‐1), which is related to atherosclerosis.

These results suggest that Lyn plays an important role in the metabolism of serum lipids and in the development of atherosclerotic lesions on high‐fat diets.
Monoallelic expresion of the odourant receptor gene and axonal projection of olfactory sensory neurones
Authors: Ishii Tomohiro , Serizawa Shou , Kohda Atsushi , Nakatani Hiroko , Shiroishi Toshihiko , Okumura Katsuzumi , Iwakura Yoichiro , Nagawa Fumikiyo , Tsuboi Akio , Sakano Hitoshi
Published: March 2003

We have previously generated transgenic mice carrying the murine odourant receptor gene, MOR28, tagged with lacZ. In this animal, the endogenous MOR28 is differently tagged with GFP. It was found that the transgenic and endogenous MOR28 genes are expressed in a mutually exclusive manner and that the two sets of olfactory sensory neurones (OSNs), each expressing either the transgenic or the endogenous MOR28, project their axons to separate glomeruli.

Our fluorescent in situ hybridization (FISH) revealed that the two endogenous alleles of MOR28 are also mutually excluded for their transcriptional activation. Therefore, we studied whether there would be any segregation in the projection of the two subsets of OSNs: one set expressing the paternal and the other expressing the maternal allele. It was found that the OSNs for both alleles shared the same glomerulus for their projection, but the projection targets were segregated within the glomerular structure.

Two subsets of neurones expressing either the transgenic or the endogenous MOR28 target their axons to two separate glomeruli based on the differences in the genetic backgrounds, nature of tagging, and chromosomal locations. In contrast, neurones expressing a maternal or paternal allele share the same glomeruli, but tend to target to segregated areas within the glomerular structure. The segregation was more prominent with increased differences in the genetic background between the two alleles.
Cross talk of the interferon‐α/β signalling complex with gp130 for effective interleukin‐6 signalling
Authors: Mitani Yukiko , Takaoka Akinori , Kim Sun Hwa , Kato Yukiko , Yokochi Taeko , Tanaka Nobuyuki , Taniguchi Tadatsugu
Published: March 2003

Background Signalling cross talk provides a molecular basis for modulating a given signalling pathway by another, and it is often critical for regulating cellular responses elicited by cytokines. Previously, we reported on the critical role of the IFN‐α/β signalling complex, generated by spontaneously produced IFN‐α/β, in efficient IFN‐γ signalling.

Results In the present study, we have demonstrated that the IFN‐α/β signalling complex also contributes to efficient IL‐6 signalling. In fact, IL‐6‐induced activation of the Stat1 and Stat3 transcription factors is markedly diminished in the absence of the IFN‐α/β signalling complex. The induction of several target genes for these factors is also diminished, both in vitro and in vivo. We provide evidence that the cytoplasmic tyrosine residues of IFNAR‐1, which remains phosphorylated by a weak IFN‐α/β stimulation, provide docking sites for Stat1 and Stat3 to form homo‐ or heterodimers following IL‐6 stimulation. Furthermore, a chemical cross‐linking experiment revealed that IFNAR‐1 and gp130, a common signal transducer for the IL‐6 family of cytokines, exist in close proximity.

Conclusions The constitutive weak IFN‐α/β signal provides a foundation for strong cellular responses to IL‐6, IFN‐γ, and possibly other cytokines. Our results also suggest the assembly of cytokine receptor subunits, which may represent a ‘receptosome’‐like structure, allowing the unique signalling cross talks to occur.
A decade of site‐ and phosphorylation state‐specific antibodies: recent advances in studies of spatiotemporal protein phosphorylation
Authors: Nagata Koh‐ichi , Izawa Ichiro , Inagaki Masaki
Published: March 2003

From 1990 to 2001, numerous site‐ and phosphorylation state‐specific antibodies have been developed and many are now commercially available. These antibodies have facilitated understanding of the cytoskeletal organization, signal transduction and transcriptional mechanisms as well as clinical diseases. This review is an attempt to cover all these aspects.
PKC1, a protein kinase C homologue of Saccharomyces cerevisiae, participates in microtubule function through the yeast EB1 homologue, BIM1
Authors: Hosotani Tomoki , Koyama Hirofumi , Uchino Masayuki , Miyakawa Tokichi , Tsuchiya Eiko
Published: March 2003

Background RSC is a chromatin‐remodelling complex of Saccharomyces cerevisiae and essential for growth. Its catalytic subunit is encoded by the NPS1/STH1 gene. At the present time, little is known regarding the cellular function of RSC.

Results To identify genes with functions related to NPS1, we screened high‐copy suppressor genes for the temperature‐ and thiabendazole (TBZ)‐sensitive mutant allele of NPS1, nps1‐105. Amongst the suppressors we cloned PKC1/STT1 and BIM1 that encoded a homologue of mammalian protein kinase C and a conserved microtubule binding protein homologous to human EB1, respectively. Both the temperature sensitive mutation of PKC1, stt1, and the bim1 null mutation caused synthetic growth defects with nps1‐105. A genetic analysis of the functional relationships between these genes revealed that PKC1 suppressed the defect of nps1‐105 through the BIM1 function but not by the activation of the MPK1/MAPK pathway. The stt1 mutation alone showed TBZ sensitivity and delayed the G2‐phase progression at semi‐permissive temperatures. Both of these stt1 phenotypes were suppressed by the over‐expression of BIM1. In addition, stt1 as well as nps1‐105, mis‐segregated a mini‐chromosome at frequencies higher than the wild‐type at a permissive temperature. The mis‐segregation was enhanced in the nps1‐105 stt1 double mutant.

Conclusion These results suggest that Pkc1p plays a role which is relevant to microtubule functions and that this role is mediated by a hitherto unknown PKC signalling pathway and by Bim1p
Interaction of fission yeast ORC with essential adenine/thymine stretches in replication origins
Authors: Takahashi Tatsuro , Masukata Hisao
Published: March 2003

Background Eukaryotic DNA replication is initiated from distinct regions on the chromosome. However, the mechanism for recognition of replication origins is not known for most eukaryotes. In fission yeast, replication origins are isolated as autonomously replicating sequences (ARSs). Multiple adenine/thymine clusters are essential for replication, but no short consensus sequences are found. In this paper, we examined the interaction of adenine/thymine clusters with the replication initiation factor ORC.

Results The SpOrc1 or SpOrc2 immunoprecipitates (IPs) containing at least four subunits of SpORC, interacted with the ars2004 fragment, which is derived from a predominant replication origin on the chromosome. SpORC‐IPs preferentially interacted with two regions of the ars2004, which consist of consecutive adenines and AAAAT repeats and are essential for ARS activity. The nucleotide sequences required for the interaction with SpORC‐IPs correspond closely to those necessary for in vivo ARS activity.

Conclusion Our results suggest that the SpORC interacts with adenine/thymine stretches, which have been shown to be the most important component in the fission yeast replication origin. The presence of multiple SpORC‐binding sites, with certain sequence variations, is characteristic for the fission yeast replication origins.
Math6, a bHLH gene expressed in the developing nervous system, regulates neuronal versus glial differentiation
Authors: Inoue Chihiro , Bae Soo‐Kyung , Takatsuka Kenji , Inoue Tomoyuki , Bessho Yasumasa , Kageyama Ryoichiro
Published: March 2003

Background Whereas multiple basic helix‐loop‐helix (bHLH) genes are expressed in the developing nervous system, they account for the differentiation of only subsets of neurones, suggesting that there may be as‐yet unidentified bHLH genes.

Results We have isolated a novel bHLH gene, designated Math6, a distant mammalian homologue of the Drosophila proneural gene atonal. Structural analysis of the Math6 gene demonstrated that the coding region is divided into three exons, whereas that of other atonal homologues is present in a single exon, indicating that the genomic structure of Math6 is unique among the atonal homologues. Math6 is initially expressed by neural precursor cells in the ventricular zone, but later by subsets of differentiating and mature neurones such as hippocampal neurones and cerebellar Purkinje cells. Mis‐expression of Math6 with retrovirus in the developing retina induced neurogenesis, while inhibiting gliogenesis, without affecting cell proliferation and death.

Conclusions These results show that cells which would normally differentiate into glia adopted the neuronal fate by mis‐expression of Math6, indicating that Math6 promotes neuronal vs. glial fate determination in the nervous system.
Distinct regulatory mechanism for p70 S6 kinase β from that for p70 S6 kinase α
Authors: Minami Taichi , Hara Kenta , Oshiro Noriko , Ueoku Sachiko , Yoshino Ken‐ichi , Tokunaga Chiharu , Shirai Yasuhito , Saito Naoaki , Gout Ivan , Yonezawa Kazuyoshi
Published: March 2003

Background A novel ribosomal S6 kinase, termed p70 S6 kinase β (p70β), has a highly homologous amino acid sequence to that of p70/p85 S6 kinase (p70α). This includes the critical phosphorylation sites, Thr252, Ser394 and Thr412 in p70α1, which correspond to Thr241, Ser383 and Thr401 in p70β1, respectively. However, the regulatory mechanism for p70β remains to be elucidated.

Results We report here the expression and the mechanism of in vivo regulation of p70β. Two isoforms, p70β1 and p70β2, were expressed in a variety of tissues at a different level. p70β1 was mainly targeted to the nucleus, whereas p70β2 dispersed throughout the cytoplasm including nucleoplasm. The kinase activity of p70β1 was less sensitive to the inhibition induced by rapamycin, wortmannin and amino acid withdrawal than that of p70α. The portion of p70β activity inhibited by rapamycin was rescued by the rapamycin‐resistant mutant of the mammalian target of rapamycin (mTOR). Mutational analysis revealed that the phosphorylation of Thr241 and Thr401 in p70β1 was indispensable for the kinase activity. In contrast, a p70β1 mutant in which Ser383 was substituted with Gly (S383G) still retained nearly the half maximal activity. Sequential phosphorylation of wild‐type and S383G mutant of p70β1 with mTOR and 3‐phosphoinositide‐dependent protein kinase 1 (PDK1) in vitro synergistically activated their kinase activities.

Conclusion These results indicate that p70β is regulated by the mTOR‐ and PDK1‐signalling pathways through a synergistic interaction between phosphorylated Thr241 and Thr401, while Ser383 plays minor role in their activation mechanism. Activated p70β may be less sensitive to dephosphorylation mediated by putative phosphatases activated by rapamycin, amino acid withdrawal, and probably wortmannin.
SPAL, a Rap‐specific GTPase activating protein, is present in the NMDA receptor‐PSD‐95 complex in the hippocampus
Authors: C. Roy Badal , Kohu Kazuyoshi , Matsuura Ken , Yanai Hiroyuki , Akiyama Tetsu
Published: March 2003

Background: The PSD‐95 family of proteins possesses multiple protein binding domains, including three PDZ domains, an SH3 domain, a HOOK domain and a guanylate kinase‐like (GK) domain. The PSD‐95 proteins function as scaffolding proteins that link ion channels such as the N‐methyl‐d‐aspartate‐receptors (NMDA‐Rs) with cytoskeletal networks and signalling molecules, thereby controlling synaptic plasticity and learning.

Results: We found that the PSD‐95 family proteins interact via their GK domains with SPA‐1‐like protein (SPAL), a GTPase‐activating protein (GAP) that is specific for Rap1. SPAL was contained within the NMDA‐R‐PSD‐95 complex, and co‐localized with PSD‐95 and NMDA‐R at the synapses in cultured hippocampal neurones. Furthermore, NMDA stimulation induced the dephosphorylation of SPAL in cultured hippocampal neurones.

Conclusion: Our findings suggest that SPAL may be involved in the NMDA‐mediated organization of cytoskeletal networks and signal transduction.
ADP stabilizes the human Rad51‐single stranded DNA complex and promotes its DNA annealing activity
Authors: Kim Hye‐Kyung , Morimatsu Katsumi , Nordén Bengt , Ardhammar Malin , Takahashi Masayuki
Published: March 2003

Background: Human Rad51 protein (HsRad51) is a homologue of Escherichia coli RecA protein, and involved in homologous recombination. These eukaryotic and bacterial proteins catalyse strand exchange between two homologous DNA molecules, each forming a complex with single‐stranded DNA (ssDNA) and ATP as the initial step. Both proteins hydrolyse ATP; however, the role of ATP hydrolysis appears to vary between the two proteins.

Results: Measurements using the fluorescence ssDNA analogue, poly(1,N6‐etheno‐deoxyadenosine), indicate that ATP affects the HsRad51–ssDNA complex, promoting two conformational states: one transient, rather rigid transition state and a final more flexible state. While ADP lowers the affinity of RecA protein to ssDNA, it is found to rather stabilize the HsRad51–ssDNA complex. ADP does not activate the strand exchange by HsRad51 but instead stimulates annealing between complementary ssDNAs.

Conclusions: The hydrolysis of ATP promotes a transition of the HsRad51–ssDNA complex from a stiff state to less stiff state. The first state may be important for the strand separation of dsDNA in the initial step of strand exchange, while the second state may be important for annealing in the next step. However, hydrolysis does not dissociate HsRad51 from DNA as a component step of its recycling.
Neuronal p38 MAPK signalling: an emerging regulator of cell fate and function in the nervous system
Authors: Takeda Kohsuke , Ichijo Hidenori
Published: March 2003

p38 mitogen‐activated protein kinases (MAPKs), together with extracellular signal‐regulated kinases (ERKs) and c‐Jun N‐terminal kinases (JNKs), constitute the MAPK family. Multiple intracellular signalling pathways that converge on MAPKs exist in all eukaryotic cells and play pivotal roles in a wide variety of cellular functions. p38 MAPKs and JNKs, also termed stress‐activated protein kinases (SAPKs), are preferentially activated by various cytotoxic stresses and cytokines and appear to be potent regulators of stress‐induced apoptosis. Whereas JNKs have been shown to play pivotal roles in the regulation of neuronal apoptosis, the role of p38 MAPKs in the nervous system is poorly understood. However, accumulating evidence from mammalian cell culture systems and the strong genetic tool C. elegans suggests that neuronal p38 signalling has diverse functions beyond the control of cell death and survival. This review focuses on possible roles for the p38 pathway in the nervous system, with principal emphasis placed on the roles in neuronal cell fate decision and function.
Interaction between apterous and early expression of vestigial in formation of the dorso‐ventral compartments in the Drosophila wing disc
Authors: Delanoue Rénald , Zider Alain , Cossard Raynald , Dutriaux Annie , Silber Jöel
Published: March 2003

Background: Compartment formation is a developmental process that requires the existence of barriers against intermixing between cell groups. In the Drosophila wing disc, the dorso‐ventral (D/V) compartment boundary is defined by the expression of the apterous (ap) selector gene in the dorsal compartment. AP activity is under control of dLMO which destabilizes the formation of the AP–CHIP complex.

Results: We report that D/V boundary formation in the wing disc also depends on early expression of vestigial (vg). Our data suggest that vg is already required for wing cell proliferation before D/V compartmentalization. In addition, we show that over‐expression of vg can, to some extent, rescue the effect of the absence of ap on D/V boundary formation. Early VG product regulates AP activity by inducing dLMO and thus indirectly regulating ap target genes such as fringe and the PSα1 and PSα2 integrins.

Conclusion: Normal cell proliferation is necessary for ap expression at the level of the D/V boundary. This would be mediated by vg, which interacts in a dose‐dependent way with ap.
Weather forecasting for dinosaurs
Authors: Valdes Paul J.
Published: March 2003

A weather forecast for 22 September 150 million years ago: ‘Most of Britain will continue to enjoy a sunny end to the summer. Winds remain calm, but some cloud may develop by the end of the day. Further afield, India and Australia are experiencing some stormy weather with severe gales across the northern coast of India.’
A geological tour of the islands of Madeira and Porto Santo
Authors: Czajkowski Michael
Published: March 2003

The Madeira archipelago is situated in the Atlantic Ocean about 900 km south‐west of Portugal and 700 km west of the Moroccan coast. The islands are volcanic and were produced by a large hotspot beneath the eastern Atlantic. The two main islands, the subject of this tour, are Madeira, the largest, and, 37 km to the north‐east, Porto Santo. There are also the three Deserta islands 16 km to the south‐east of Madeira which are uninhabited and are now a nature reserve.
Explicit expressions and numerical calculations for the Fréchet and second derivatives in 2.5D Helmholtz equation inversion
Authors: Bing Zhou , Greenhalgh
Published: March 2003

In order to perform resistivity imaging, seismic waveform tomography or sensitivity analysis of geophysical data, the Fréchet derivatives, and even the second derivatives of the data with respect to the model parameters, may be required. We develop a practical method to compute the relevant derivatives for 2.5D resistivity and 2.5D frequency‐domain acoustic velocity inversion. Both geophysical inversions entail the solution of a 2.5D Helmholtz equation. First, using differential calculus and the Green's functions of the 2.5D Helmholtz equation, we strictly formulate the explicit expressions for the Fréchet and second derivatives, then apply the finite‐element method to approximate the Green's functions of an arbitrary medium. Finally, we calculate the derivatives using the expressions and the numerical solutions of the Green's functions. Two model parametrization approaches, constant‐point and constant‐block, are suggested and the computational efficiencies are compared. Numerical examples of the derivatives for various electrode arrays in cross‐hole resistivity imaging and for cross‐hole seismic surveying are demonstrated. Two synthetic experiments of resistivity and acoustic velocity imaging are used to illustrate the method.
Multifold borehole radar acquisition and processing
Authors: Hollender Fabrice , Tillard Sylvie , Corin Laurent
Published: March 2003

The multifold acquisition principle was applied to a borehole radar survey, performed in a granitic site (Grimsel Test Site, Switzerland). Two multifold coverage acquisitions (40‐fold and 20‐fold) were carried out in a subhorizontal borehole. Instrumental drifts (transmission time and sampling frequency fluctuations) were corrected in order to remove shifts observed on CMP gathers and to optimize velocity analysis and trace stacking. Computation of velocity spectra was adapted in order to take into account the features of the medium investigated (homogeneous velocity, various reflector orientations). The NMO velocities were then interpreted as angles between reflectors and the survey line. The processing, based on the computation of several constant velocity stacked sections performed with different NMO velocities, leads to better results than the standard DMO + NMO processing. The signal‐to‐noise ratio of the stacked profile is improved in comparison with the single‐fold section, which results from a standard acquisition. From a practical point of view, the implementation of a multifold radar survey within a borehole is difficult but a greater investigation range is obtained, more reflectors are detected and the mapping of geological discontinuities is improved.
Sensitivity of reflection seismic data to oil‐column height in high‐porosity sandstones
Authors: Ryan‐Grigor Sarah , Sayers Colin M.
Published: March 2003

Tuning is the effect of interference between the reflections from the top and bottom of a thin layer on the amplitude of the composite reflection. For a homogeneous sandstone reservoir containing an oil column overlying brine, interference between the reflection from the top reservoir and the oil/water contact is a function of the height of the oil column. If the properties of the sandstone do not vary across the oil/water contact, the SS, PS and SP reflection coefficients from the oil/water contact are small in comparison to the PP reflection coefficient. This allows analytic expressions for the effective PP and PS reflection coefficients from the reservoir to be derived that include all P‐wave multiples within the oil column. For a given source/receiver offset, the component of the wavevector inside the oil column normal to the interface is larger for the PPPP reflection than for the PPPS reflection, due to the asymmetry in the raypath for the PPPS reflection. The PPPS reflection is therefore useful for determining oil‐column heights larger than that discriminated by the PPPP reflection, especially when used at wider offsets.

A convenient classification of the AVO response of hydrocarbon‐bearing sandstone reservoirs overlain by shale is the scheme of Rutherford and Williams. Class 1 sands have higher acoustic impedance for normal incidence than the overlying shale, Class 2 sands have nearly the same acoustic impedance as the shale and Class 3 sands have lower acoustic impedance. Synthetic shot gathers calculated for these three classes as a function of oil‐column height show that a combination of the PPPP and the PPPS amplitudes can be plotted as a tuning trajectory, which can be used to determine the oil‐column height. This method is most sensitive for reservoirs that belong to AVO classes 1 and 2, and therefore may be useful in AVO analysis of Class 1 and 2 reservoirs where the traditional AVO indicators (developed for Class 3 reservoirs) do not work very well. These results demonstrate the usefulness of shear waves recorded in the marine environment at wide offsets.
Constant normal‐moveout (CNMO) correction: a technique and test results
Authors: Shatilo Andrew , Aminzadeh Fred
Published: March 2003

We introduce a processing technique which minimizes the ‘stretching effects’ of conventional NMO correction. Unlike conventional NMO, the technique implies constant normal moveout (CNMO) for a finite time interval of a seismic trace. The benefits of the proposed method include preservation of higher frequencies and reduction of spectral distortions at far offsets. The need for severe muting after the correction is reduced, allowing longer spreads for stack, velocity and AVO analysis. The proposed technique has been tested on model and real data. The method may improve the resolution of CMP stack and AVO attribute analysis. The only assumptions for this stretch‐free NMO correction are (i) all time samples of a digital reflected wavelet at a particular offset have the same normal moveout, and (ii) reflection records have an interference nature.
Horizontal‐loop electromagnetic signature of a buried dike, Al Quweira area, southwest Jordan
Authors: Batayneh Awni T.
Published: March 2003

During 1999, horizontal‐loop electromagnetic (HLEM) measurements were made over a buried dike in the Al Quweira area, southwest Jordan, using the APEX MAX MIN III instrument, as part of a mineral exploration project. The objectives of the study were (i) to evaluate the resolution of the HLEM technique in field work in detecting and locating anomalies caused by vein‐like bodies, and (ii) to assess the capability of HLEM surveys for detecting targets in other locations throughout our geophysical survey programme. In‐phase and quadrature anomalies were recorded with 50 m and 100 m coil separations and multiple frequencies across the strike of the buried dike. Data recorded at 43 locations, spaced 10 m apart along the survey line, were interpreted quantitatively. For a 50 m separation, corresponding to shallow depths of investigation, the results do not show any recognizable response from the buried dike. The HLEM data were modelled using a three‐layer structure in order to estimate the thickness of the weathering layer along the survey line. Conversely, data obtained with a 100 m separation, corresponding to moderate depths of investigation, reveal significant anomalies from the buried dike at high frequencies. A phasor or vector diagram was used to calculate the response parameter, depth and dip of the buried dike.
On the effectiveness of 2D electrical inversion results: an agricultural case study
Authors: Panissod C. , Michot D. , Benderitter Y. , Tabbagh A.
Published: March 2003

Electrical resistivity tomography was used in Beauce (France) to assess the water extraction by corn plants (evapotranspiration). The acquired pseudosections show conductive anomalies under the plants. A 2D inversion of measurements led us to identify clear resistive features associated with the water losses under the corn‐plant rows. New models have been calculated with two different 3D algorithms (finite‐difference and moment‐method) to take into account 3D structure of the ground and to confirm that periodic resistive features may generate shifted apparent‐resistivity anomalies.
P‐wave stacking‐velocity tomography for VTI media
Authors: Grechka Vladimir , Pech Andres , Tsvankin Ilya
Published: March 2003

A major complication caused by anisotropy in velocity analysis and imaging is the uncertainty in estimating the vertical velocity and depth scale of the model from surface data. For laterally homogeneous VTI (transversely isotropic with a vertical symmetry axis) media above the target reflector, P‐wave moveout has to be combined with other information (e.g. borehole data or converted waves) to build velocity models for depth imaging. The presence of lateral heterogeneity in the overburden creates the dependence of P‐wave reflection data on all three relevant parameters (the vertical velocity VP0 and the Thomsen coefficients ε and δ) and, therefore, may help to determine the depth scale of the velocity field.

Here, we propose a tomographic algorithm designed to invert NMO ellipses (obtained from azimuthally varying stacking velocities) and zero‐offset traveltimes of P‐waves for the parameters of homogeneous VTI layers separated by either plane dipping or curved interfaces. For plane non‐intersecting layer boundaries, the interval parameters cannot be recovered from P‐wave moveout in a unique way. Nonetheless, if the reflectors have sufficiently different azimuths, a priori knowledge of any single interval parameter makes it possible to reconstruct the whole model in depth. For example, the parameter estimation becomes unique if the subsurface layer is known to be isotropic. In the case of 2D inversion on the dip line of co‐orientated reflectors, it is necessary to specify one parameter (e.g. the vertical velocity) per layer.

Despite the higher complexity of models with curved interfaces, the increased angle coverage of reflected rays helps to resolve the trade‐offs between the medium parameters. Singular value decomposition (SVD) shows that in the presence of sufficient interface curvature all parameters needed for anisotropic depth processing can be obtained solely from conventional‐spread P‐wave moveout. By performing tests on noise‐contaminated data we demonstrate that the tomographic inversion procedure reconstructs both the interfaces and the VTI parameters with high accuracy. Both SVD analysis and moveout inversion are implemented using an efficient modelling technique based on the theory of NMO‐velocity surfaces generalized for wave propagation through curved interfaces.
Depth imaging in anisotropic media by symmetric non‐stationary phase shift
Authors: Ferguson Robert J. , Margrave Gary F.
Published: March 2003

We present a new depth‐imaging method for seismic data in heterogeneous anisotropic media. This recursive explicit method uses a non‐stationary extrapolation operator to allow lateral velocity variation, and it uses the relationship between phase angle and the spectral coordinates of seismic data to allow velocity variation with phase angle. A qualitative comparison of migration impulse responses suggests that, for an equivalent cost, the symmetric non‐stationary phase‐shift (SNPS) operator is superior to the phase‐shift plus interpolation (PSPI) operator, for very large depth intervals. To demonstrate the potential of the new method, seismic data from a physical model acquired over a transversely isotropic medium are imaged using a shot‐record migration based on the SNPS operator.
3D free‐boundary conditions for coordinate‐transform finite‐difference seismic modelling
Authors: Hestholm Stig , Ruud Bent
Published: March 2003

New alternative formulations of exact boundary conditions for arbitrary three‐dimensional (3D) free‐surface topographies on seismic media have been derived. They are shown to be equivalent to previously published formulations, thereby verifying the validity of each set of formulations. The top of a curved grid represents the free‐surface topography while the interior of the grid represents the physical medium. We assume the velocity–stress version of the viscoelastic wave equations to be valid in this grid before transforming the equations to a rectangular grid. In order to perform the numerical discretization we apply the latter version of the equations for seismic wave propagation simulation in the medium. The numerical discretization of the free‐surface topography boundary conditions by second‐order finite differences (FDs) is shown, as well as the spatially unconditional stability of the resulting system of equations. The FD order is increased by two for each point away from the free surface up to eight, which is the order used in the interior. We use staggered grids in both space and time and the second‐order leap‐frog and Crank– Nicholson methods for wavefield time propagation. An application using parameters typical of teleseismic earthquakes and explosions is presented using a 200 × 100 km2 area of real topography from southwestern Norway over a homogeneous medium. A dipping plane wave simulates a teleseismic P‐wave incident on the surface topography. Results show conversion from P‐ to Rg‐ (short period fundamental mode Rayleigh) waves in the steepest and/or roughest topography, as well as attenuated waves in valleys and fjords. The codes are parallelized for simulation on fast supercomputers and PC‐clusters to model high frequencies and/or large areas.
Growth, light interception and yield responses of spring wheat (Triticum aestivum L.) grown under elevated CO2 and O3 in open‐top chambers
Authors: Mulholland B. J. , Craigon J. , Black C. R. , Colls J. J. , Atherton J. , Landon G.
Published: March 2003

Spring wheat cv. Minaret was grown to maturity under three carbon dioxide (CO2) and two ozone (O3) concentrations in open‐top chambers (OTC). Green leaf area index (LAI) was increased by elevated CO2 under ambient O3 conditions as a direct result of increases in tillering, rather than individual leaf areas. Yellow LAI was also greater in the 550 and 680 μmol mol–1 CO2 treatments than in the chambered ambient control; individual leaves on the main shoot senesced more rapidly under 550 μmol mol–1 CO2, but senescence was delayed at 680 μmol mol–1 CO2. Fractional light interception (f) during the vegetative period was up to 26% greater under 680 μmol mol–1 CO2 than in the control treatment, but seasonal accumulated intercepted radiation was only increased by 8%. As a result of greater carbon assimilation during canopy development, plants grown under elevated CO2 were taller at anthesis and stem and ear biomass were 27 and 16% greater than in control plants. At maturity, yield was 30% greater in the 680 μmol mol–1 CO2 treatment, due to a combination of increases in the number of ears per m–2, grain number per ear and individual grain weight (IGW).

Exposure to a seasonal mean (7 h d–1) of 84 nmol mol–1 O3 under ambient CO2 decreased green LAI and increased yellow LAI, thereby reducing both f and accumulated intercepted radiation by ≈ 16%. Individual leaves senesced completely 7–28 days earlier than in control plants. At anthesis, the plants were shorter than controls and exhibited reductions in stem and ear biomass of 15 and 23%. Grain yield at maturity was decreased by 30% due to a combination of reductions in ear number m–2, the numbers of grains per spikelet and per ear and IGW. The presence of elevated CO2 reduced the rate of O3‐induced leaf senescence and resulted in the maintenance of a higher green LAI during vegetative growth under ambient CO2 conditions. Grain yields at maturity were nevertheless lower than those obtained in the corresponding elevated CO2 treatments in the absence of elevated O3. Thus, although the presence of elevated CO2 reduced the damaging impact of ozone on radiation interception and vegetative growth, substantial yield losses were nevertheless induced. These data suggest that spring wheat may be susceptible to O3‐induced injury during anthesis irrespective of the atmospheric CO2 concentration. Possible deleterious mechanisms operating through effects on pollen viability, seed set and the duration of grain filling are discussed.
Impact of elevated atmospheric CO2concentration on soil microbial biomass and activity in a complex, weedy field model ecosystem
Authors: Kampichler Christian , Kandeler Ellen , Bardgett Richard D. , Jones T. Hefin , Thompson Lindsey J.
Published: March 2003

Although soil organisms play an essential role in the cycling of elements in terrestrial ecosystems, little is known of the impact of increasing atmospheric CO2concentrations on soil microbial processes. We determined microbial biomass and activity in the soil of multitrophic model ecosystems housed in the Ecotron (NERC Centre for Population Biology, Ascot, UK) under two atmospheric CO2concentrations (ambient vs. ambient + 200 ppm). The model communities consist of four annual plant species which naturally co‐occur in weedy fields and disturbed ground throughout southern England, together with their herbivores, parasitoids and soil biota. At the end of two experimental runs lasting 9 and 4.5 months, respectively, root dry weight and quality showed contradictory responses to elevated CO2concentrations, probably as a consequence of the different time‐periods (and hence number of plant generations) in the two experiments. Despite significant root responses no differences in microbial biomass could be detected. Effects of CO2concentration on microbial activity were also negligible. Specific enzymes (protease and xylanase) showed a significant decrease in activity in one of the experimental runs. This could be related to the higher C:N ratio of root tissue. We compare the results with data from the literature and conclude that the response of complex communities cannot be predicted on the basis of oversimplified experimental set‐ups.
Global change and root function
Authors: VAN NOORDWIJK MEINE , MARTIKAINEN PERTTI , BOTTNER PIERRE , CUEVAS ELVIRA , ROULAND CORNINE , DHILLION SHIVCHARN S.
Published: March 2003

Global change includes land‐use change, elevated CO2concentrations, increased temperature and increased rainfall variability. All four aspects by themselves and in combination will influence the role of roots in linking below‐ and above‐ground ecosystem function via organic and inorganic resource flows. Root‐mediated ecosystem functions which may be modified by global change include below‐ground resource (water, nutrients) capture, creation and exploitation of spatial heterogeneity, buffering of temporal variations in above‐ground factors, supply and storage of C and nutrients to the below‐ground ecosystem, mobilization of nutrients and C from stored soil reserves, and gas exchange between soil and atmosphere including the emission from soil of greenhouse gases.

The theory of a functional equilibrium between root and shoot allocation is used to explore predicted responses to elevated CO2in relation to water or nutrient supply as limiting root function. The theory predicts no change in root:shoot allocation where water uptake is the limiting root function, but substantial shifts where nutrient uptake is (or becomes) the limiting function. Root turnover will not likely be influenced by elevated CO2, but by changes in regularity of water supply. A number of possible mechanisms for root‐mediated N mineralization is discussed in the light of climate change factors. Rhizovory (root consumption) may increase under global change as the balance between plant chemical defense and adapted root consuming organisms may be modified during biome shifts in response to climate change. Root‐mediated gas exchange allows oxygen to penetrate into soils and methane (CH4) to escape from wetland soils of tundra ecosystems as well as tropical rice production systems. The effect on net greenhouse gas emissions of biome shifts (fens replacing bogs) as well as of agricultural land management will depend partly on aerenchyma in roots.
Global change, soil biodiversity, and nitrogen cycling in terrestrial ecosystems: three case studies
Authors: SWIFT M. J. , ANDRÉN O. , BRUSSAARD L. , BRIONES M. , COUTEAUX M. ‐M. , EKSCHMITT K. , KJOLLER A. , LOISEAU P. , SMITH P.
Published: March 2003

The relative contribution of different soil organism groups to nutrient cycling has been quantified for a number of ecosystems. Some functions, particularly within the N‐cycle, are carried out by very specific organisms. Others, including those of decomposition and nutrient release from organic inputs are, however, mediated by a diverse group of bacteria, protozoa, fungi and invertebrate animals. Many authors have hypothesized that there is a high degree of equivalence and flexibility in function within this decomposer community and thence a substantial extent of redundancy in species richness and resilience in functional capacity. Three case studies are presented to examine the relationship between soil biodiversity and nitrogen cycling under global change in ecosystem types from three latitudes, i.e. tundra, temperate grassland and tropical rainforest.

In all three ecosystems evidence exists for the potential impact of global change factors (temperature change, CO2enrichment, land‐use‐change) on the composition and diversity of the soil community as well as on various aspects of the nitrogen and other cycles. There is, however, very little unequivocal evidence of direct causal linkage between species richness and nutrient cycling efficiency. Most of the changes detected are shifts in the influence of major functional groups of the soil biota (e.g. between microflora and fauna in decomposition). There seem to be few data, however, from which to judge the significance of changes in diversity within functional groups. Nonetheless the soil biota are hypothesized to be a sensitive link between plant detritus and the availability of nutrients to plant uptake. Any factors affecting the quantity or quality of plant detritus is likely to change this link. Rigorous experimentation on the relationships between soil species richness and the regulation or resilience of nutrient cycles under global change thus remains a high priority.
The effect of experimental ecosystem warming on CO2 fluxes in a montane meadow
Authors: Saleska Scott R. , Harte JohN. , Torn Margaret S.
Published: March 2003

Climatic change is predicted to alter rates of soil respiration and assimilation of carbon by plants. Net loss of carbon from ecosystems would form a positive feedback enhancing anthropogenic global warming. We tested the effect of increased heat input, one of the most certain impacts of global warming, on net ecosystem carbon exchange in a Rocky Mountain montane meadow. Overhead heaters were used to increase the radiative heat flux into plots spanning a moisture and vegetation gradient. We measured net whole‐ecosystem CO2 fluxes using a closed‐path chamber system, relatively nondisturbing bases, and a simple model to compensate for both slow chamber leaks and the CO2 concentration‐dependence of photosynthetic uptake, in 1993 and 1994. In 1994, we also measured soil respiration separately. The heating treatment altered the timing and magnitude of net carbon fluxes into the dry zone of the plots in 1993 (reducing uptake by ≈100 g carbon m–2), but had an undetectable effect on carbon fluxes into the moist zone. During a strong drought year (1994), heating altered the timing, but did not significantly alter the cumulative magnitude, of net carbon uptake in the dry zone. Soil respiration measurements showed that when differences were detected in dry zone carbon fluxes, they were caused by changes in carbon input from photosynthesis, not by temperature‐driven changes in carbon output from soil respiration. When differences were detected in dry‐zone carbon fluxes, they were caused by changes in carbon input from photosynthesis, not by a temperature‐driven changes in carbon output from soil respiration. Regression analysis suggested that the reduction in carbon inputs from plants was due to a combination of two soil moisture effects: a direct physiological response to decreased soil moisture, and a shift in plant community composition from high‐productivity species to low‐productivity species that are more drought tolerant. These results partially support predictions that warming may cause net carbon losses from some terrestrial ecosystems. They also suggest, however, that changes in soil moisture caused by global warming may be as important in driving ecosystem response as the direct effects of increased soil temperature.
Seasonal trends of gross N mineralization in a natural calcareous grassland
Authors: Jamieson Nicola , Monaghan RosS. , Barraclough Declan
Published: March 2003

The effect of climate change on biologically mediated soil processes is likely to be complex and difficult to predict. The direct effect of changes in soil moisture and temperature may be obscured or even reversed by changes in the return of organic substrates to the soil. This paper is the first in a series reporting the results from a medium‐term investigation into the effect of simulated climate change on soil N mineralization in a seminatural calcareous grassland in southern England. Gross rates of N mineralization were determined by isotope dilution in plots subjected to winter warming (3 °C above ambient), enhanced or decreased summer rainfall and combinations of these treatments. The results from the control treatment, reported here, show a strong seasonality of gross N mineralization with rates highest in the Spring and Autumn and lowest in Summer. They indicate that water availability is the main restraint on microbial processes and plant growth and that, in the short term, enhanced summer rainfall is likely to be the main factor influencing nutrient turnover. Further papers will report the results from the imposed treatments.
Carry‐over of enhanced ultraviolet‐B exposure effects to successive generations of a desert annual: interaction with atmospheric CO2 and nutrient supply
Authors: Musil C. F. , Midgley G. F. , Wand S. J. E.
Published: March 2003

The performance of fifth generation offspring of a desert annual (Dimorphotheca sinuataDC.) were compared in the absence of UV‐B, under variable atmospheric CO2and nutrient supply, after four consecutive generations of concurrent exposure of their progenitors to UV‐B at ambient (seasonal range: 2.55–8.85 kJ m–2d–1) and enhanced (seasonal range: 4.70–11.41 kJ m–2d–1) levels. Offspring of progenitors grown under elevated UV‐B exhibited a diminished photosynthetic rate, a consequence of a reduced leaf density, and diminished foliar levels of carotenoids, polyphenolics and anthocyanins. Conversely, nonstructural carbohydrate and chlorophyllblevels were increased. Altered physiology was accompanied by reduced apical dominance and earlier flowering, features generally considered under photomorphogenic control, increased branching and inflorescence production and greater partitioning of biomass to reproductive structures, but diminished seed production. Many of these changes were magnified under nutrient limitation and intensified under atmospheric CO2enriched conditions. The latter disagrees with current opinion that elevated CO2may reduce detrimental UV‐B effects, at least over the long‐term. Observed correlations between seed production and polyphenolic, especially anthocyanin, levels in offspring, and indications of diminished lignification (thinner leaves, less robust stems and fewer lignified seeds set) all pointed to the involvement of the phenylpropanoid pathway in seed formation and plant structural development and its disruption during long‐term UV‐B exposure. Comparisons with earlier generations revealed trends with cumulative generations of enhanced UV‐B exposure of increasing chlorophyll b and nonstructural carbohydrates, decreasing polyphenolics and biomass allocation to vegetative structures, and diminishing seed production despite increasing biomass allocation to reproductive structures. Notwithstanding some physiological compensation (increased chlorophyll b), the accumulation and persistence of these ostensibly inherited changes in physiological and reproductive performance suggest a greater impact of elevated UV‐B on vegetation, primary production and regeneration over the long‐term than presently envisaged.