Showing papers by "Durham University published in 1998"

Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds

Abstract: We present a full-sky 100 μm map that is a reprocessed composite of the COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and confirmed point sources removed. Before using the ISSA maps, we remove the remaining artifacts from the IRAS scan pattern. Using the DIRBE 100 and 240 μm data, we have constructed a map of the dust temperature so that the 100 μm map may be converted to a map proportional to dust column density. The dust temperature varies from 17 to 21 K, which is modest but does modify the estimate of the dust column by a factor of 5. The result of these manipulations is a map with DIRBE quality calibration and IRAS resolution. A wealth of filamentary detail is apparent on many different scales at all Galactic latitudes. In high-latitude regions, the dust map correlates well with maps of H I emission, but deviations are coherent in the sky and are especially conspicuous in regions of saturation of H I emission toward denser clouds and of formation of H2 in molecular clouds. In contrast, high-velocity H I clouds are deficient in dust emission, as expected. To generate the full-sky dust maps, we must first remove zodiacal light contamination, as well as a possible cosmic infrared background (CIB). This is done via a regression analysis of the 100 μm DIRBE map against the Leiden-Dwingeloo map of H I emission, with corrections for the zodiacal light via a suitable expansion of the DIRBE 25 μm flux. This procedure removes virtually all traces of the zodiacal foreground. For the 100 μm map no significant CIB is detected. At longer wavelengths, where the zodiacal contamination is weaker, we detect the CIB at surprisingly high flux levels of 32 ± 13 nW m-2 sr-1 at 140 μm and of 17 ± 4 nW m-2 sr-1 at 240 μm (95% confidence). This integrated flux ~2 times that extrapolated from optical galaxies in the Hubble Deep Field. The primary use of these maps is likely to be as a new estimator of Galactic extinction. To calibrate our maps, we assume a standard reddening law and use the colors of elliptical galaxies to measure the reddening per unit flux density of 100 μm emission. We find consistent calibration using the B-R color distribution of a sample of the 106 brightest cluster ellipticals, as well as a sample of 384 ellipticals with B-V and Mg line strength measurements. For the latter sample, we use the correlation of intrinsic B-V versus Mg2 index to tighten the power of the test greatly. We demonstrate that the new maps are twice as accurate as the older Burstein-Heiles reddening estimates in regions of low and moderate reddening. The maps are expected to be significantly more accurate in regions of high reddening. These dust maps will also be useful for estimating millimeter emission that contaminates cosmic microwave background radiation experiments and for estimating soft X-ray absorption. We describe how to access our maps readily for general use.

Assessing the accuracy of remotely sensed data : principles and practices

Abstract: Introduction Why Accuracy Assessment? Overview Historical Review Aerial Photography Digital Assessments Data Collection Considerations Classification Scheme Statistical Considerations Data Distribution Randomness Spatial Autocorrelation Sample Size Sampling Scheme Sample Unit Reference Data Collection Basic Collection Forms Basic Analysis Techniques Non-Site Specific Assessments Site Specific Assessments Area Estimation/Correction Practicals Impact of Sample Design on Cost Recommendations for Collecting Reference Data ASources of Variation in Reference Data Photo Interpretation vs. Ground Visitation Interpreter Variability Observations vs. Measurements What is Correct? Labeling Map vs. Labeling the Reference Data Qualitative vs. Quantitative Analysis Local vs. Regional vs. Global Assessments Advanced Topics Beyond the Error Matrix Modifying the Error Matrix Fuzzy Set Theory Measuring Variability Complex Data Sets Change Detection Multi-Layer Assessments California Hardwood Rangeland Monitoring Project Case Study Balancing Statistical Validity with Practical Reality Bibliography

Potent suppression of hiv-1 replication in humans by t-20, a peptide inhibitor of gp41-mediated virus entry

Abstract: T-20, a synthetic peptide corresponding to a region of the transmembrane subunit of the HIV-1 envelope protein, blocks cell fusion and viral entry at concentrations of less than 2 ng/ml in vitro. We administered intravenous T-20 (monotherapy) for 14 days to sixteen HIV-infected adults in four dose groups (3, 10, 30 and 100 mg twice daily). There were significant, dose-related declines in plasma HIV RNA in all subjects who received higher dose levels. All four subjects receiving 100 mg twice daily had a decline in plasma HIV RNA to less than 500 copies/ml, by bDNA assay. A sensitive RT-PCR assay (detection threshold 40 copies/ml) demonstrated that, although undetectable levels were not achieved in the 14-day dosing period, there was a 1.96 log10 median decline in plasma HIV RNA in these subjects. This study provides proof-of-concept that viral entry can be successfully blocked in vivo. Short-term administration of T-20 seems safe and provides potent inhibition of HIV replication comparable to anti-retroviral regimens approved at present.

Resolving the Structure of Cold Dark Matter Halos

Abstract: We examine the effects of mass resolution and force softening on the density profiles of cold dark matter halos that form within cosmological N-body simulations. As we increase the mass and force resolution, we resolve progenitor halos that collapse at higher redshifts and have very high densities. At our highest resolution we have nearly 3×106 particles within the virial radius, which is several orders of magnitude more than previously used, and we can resolve more than 1000 surviving dark matter halos within this single virialized system. The halo profiles become steeper in the central regions, and we may not have achieved convergence to a unique slope within the inner 10% of the virialized region. Results from two very high resolution halo simulations yield steep inner density profiles, ρ(r)~r−1.4. The abundance and properties of arcs formed within this potential will be different from calculations based on lower resolution simulations. The kinematics of disks within such a steep potential may prove problematic for the cold dark matter model when compared with the observed properties of halos on galactic scales.

Saturation effects in deep inelastic scattering at low Q 2 and its implications on diffraction

Abstract: We present a model based on the concept of saturation for small ${Q}^{2}$ and small $x.$ With only three parameters we achieve a good description of all deep inelastic scattering data below $x=0.01.$ This includes a consistent treatment of charm and a successful extrapolation into the photoproduction regime. The same model leads to a roughly constant ratio of diffractive and inclusive cross section.

Morphological Transformation from Galaxy Harassment

Abstract: Galaxy morphologies in clusters have undergone a remarkable transition over the past several billion yr. Distant clusters at z ~ 0.4 are filled with small spiral galaxies, many of which are disturbed and show evidence of multiple bursts of star formation. This population is absent from nearby clusters, where spheroidals comprise the faint end of the luminosity function. Our numerical simulations follow the evolution of disk galaxies in a rich cluster resulting from encounters with brighter galaxies and the cluster's tidal field, or galaxy harassment. After a bursting transient phase, they undergo a complete morphological transformation from disks to spheroidals. We examine the remnants and find support for our theory in detailed comparisons of the photometry and kinematics of the spheroidal galaxies in clusters. Our model naturally accounts for the intermediate-age stellar population seen in these spheroidals, as well as for the trend in the dwarf-to-giant ratio with cluster richness. The final shapes are typically prolate and are flattened primarily by velocity anisotropy. Their mass-to-light ratios are in the range 3-8, in good agreement with observations.

Peridotites from the Izu-Bonin-Mariana Forearc (ODP Leg 125): Evidence for Mantle Melting and Melt-Mantle Interaction in a Supra-Subduction Zone Setting

Abstract: Ocean Drilling Program Leg 125 recovered serpentinized harzburgites and dunites from a total of five sites on the crests and flanks of two serpentinite seamounts, Conical Seamount in the Mariana forearc and Torishima Forearc Seamount in the Izu–Bonin forearc. These are some of the first extant forearc peridotites reported in the literature and they provide a window into oceanic, supra-subduction zone (SSZ) mantle processes. Harzburgites from both seamounts are very refractory with low modal clinopyroxene (<4%), chrome-rich spinels (cr-number = 0.40–0.80), very low incompatible element contents, and (with the exception of amphibole-bearing samples) U-shaped rare earth element (REE) profiles with positive Eu anomalies. Both sets of peridotites have olivine–spinel equilibration temperatures that are low compared with abyssal peridotites, possibly because of water-assisted diffusional equilibration in the SSZ environment. However, other features indicate that the harzburgites from the two seamounts have very different origins. Harzburgites from Conical Seamount are characterized by calculated oxygen fugacities between FMQ (fayalite–magnetite–quartz) – 1.1 (log units) and FMQ + 0.4 which overlap those of mid-ocean ridge basalt (MORB) peridotites. Dunites from Conical Seamount contain small amounts of clinopyroxene, orthopyroxene and amphibole and are light REE (LREE) enriched. Moreover, they are considerably more oxidized than the harzburgites to which they are spatially related, with calculated oxygen fugacities of FMQ – 0.2 to FMQ + 1.2. Using textural and geochemical evidence, we interpret these harzburgites as residual MORB mantle (from 15 to 20% fractional melting) which has subsequently been modified by interaction with boninitic melt within the mantle wedge, and these dunites as zones of focusing of this melt in which pyroxene has preferentially been dissolved from the harzburgite protolith. In contrast, harzburgites from Torishima Forearc Seamount give calculated oxygen fugacities between FMQ + 0.8 and FMQ + 1.6, similar to those calculated for other subduction-zone related peridotites and similar to those calculated for the dunites (FMQ + 1.2 to FMQ + 1.8) from the same seamount. In this case, we interpret both the harzburgites and dunites as linked to mantle melting (20–25% fractional melting) in a supra-subduction zone environment. The results thus indicate that the forearc is underlain by at least two types of mantle lithosphere, one being trapped or accreted oceanic lithosphere, the other being lithosphere formed by subduction-related melting. They also demonstrate that both types of mantle lithosphere may have undergone extensive interaction with subduction-derived magmas.

Environmental education in the 21st century

Abstract: Section 1: History and Development of Environmental Education Section 2: The Global Agenda Section 3: Perspectives on Theory and Research in Environmental Education Section 4: Environmental Education: Structure and Practice Section 5: The Global Scene Section 6: Towards Progress and Promise in the 21st Century

Indium-tin oxide treatments for single- and double-layer polymeric light-emitting diodes: The relation between the anode physical, chemical, and morphological properties and the device performance

Abstract: We report combined studies of the influence of chemical and physical treatments on the properties of indium–tin oxide (ITO) thin films. The ITO films were also used as transparent anodes of polymeric light-emitting diodes (LEDs) incorporating poly(p-phenylene vinylene) (PPV) as the emitter material, with, or without, doped poly(3,4-ethylene dioxythiophene) (PEDOT) as a hole-injection/transport layer. Structures based on a soluble green derivative of PPV, poly(4,4′-diphenylene diphenylvinylene) were also tested. We studied chemical (aquaregia, degreasing, RCA protocol) and physical (oxygen and argon plasmas, Teflon, and paper rubbing) treatments and, in contrast to recently published work, we find that for Balzer Baltracon ITO, oxygen plasma and not aquaregia yields the highest efficiencies and luminances and the lowest drive voltages. For oxygen-plasma-treated anodes, the device efficiency clearly correlates with the value of the ITO surface work function, which in turn depends on the time of treatment. I...

erbB-2, p53, and Efficacy of Adjuvant Therapy in Lymph Node-Positive Breast Cancer

Abstract: Background We have previously reported that high expression of the erbB-2 gene (also known as HER-2/neu and ERBB2) in breast cancer is associated with patient response to dose-intensive treatment with cyclophosphamide, doxorubicin (Adriamycin), and 5-flurouracil (CAF) on the basis of short-term follow-up of 397 patients (set A) with axillary lymph node-positive tumors who were enrolled in Cancer and Leukemia Group B (CALGB) protocol 8541. Methods To validate those findings, we conducted immunohistochemical analyses of erbB-2 and p53 protein expression in an additional cohort of 595 patients (set B) from CALGB 8541, as well as a molecular analysis of erbB-2 gene amplification in tumors from all patients (sets A and B). Marker data were compared with clinical, histologic, treatment, and outcome data. Results Updated analyses of data from set A (median follow-up, 10.4 years) showed an even stronger interaction between erbB-2 expression and CAF dose, by use of either immunohistochemical or molecular data. A similar interaction between erbB-2 expression and CAF dose was observed in all 992 patients, analyzed as a single group. However, for set B alone (median follow-up, 8.2 years), results varied with the method of statistical analysis. By use of a proportional hazards model, the erbB-2 expression-CAF dose interaction was not significant for all patients. However, in the subgroups of patients randomly assigned to the high- or the moderate-dose arms, significance was achieved. When patient data were adjusted for differences by use of a prognostic index (to balance an apparent failure of randomization in the low-dose arm), the erbB-2 expression-CAF dose interaction was significant in all patients from the validation set B as well. An interaction was also observed between p53 immunopositivity and CAF dose. Conclusions The hypothesis that patients whose breast tumors exhibit high erbB-2 expression benefit from dose-intensive CAF should be further validated before clinical implementation. Interactions between erbB-2 expression, p53 expression, and CAF dose underscore the complexities of predictive markers where multiple interactions may confound the outcome.

Evolution of Structure in Cold Dark Matter Universes

Abstract: We present an analysis of the clustering evolution of dark matter in four cold dark matter (CDM) cosmologies. We use a suite of high-resolution, 17 million particle, N-body simulations that sample volumes large enough to give clustering statistics with unprecedented accuracy. We investigate a flat model with Ω0 = 0.3, an open model also with Ω0 = 0.3, and two models with Ω = 1, one with the standard CDM power spectrum and the other with the same power spectrum as the Ω0 = 0.3 models. In all cases, the amplitude of primordial fluctuations is set so that the models reproduce the observed abundance of rich galaxy clusters by the present day. We compute mass two-point correlation functions and power spectra over 3 orders of magnitude in spatial scale and find that in all of our simulations they differ significantly from those of the observed galaxy distribution, in both shape and amplitude. Thus, for any of these models to provide an acceptable representation of reality, the distribution of galaxies must be biased relative to the mass in a nontrivial, scale-dependent fashion. In the Ω = 1 models, the required bias is always greater than unity, but in the Ω0 = 0.3 models, an "antibias" is required on scales smaller than ~5 h-1 Mpc. The mass correlation functions in the simulations are well fit by recently published analytic models. The velocity fields are remarkably similar in all the models, whether they are characterized as bulk flows, single-particle, or pairwise velocity dispersions. This similarity is a direct consequence of our adopted normalization and runs contrary to the common belief that the amplitude of the observed galaxy velocity fields can be used to constrain the value of Ω0. The small-scale pairwise velocity dispersion of the dark matter is somewhat larger than recent determinations from galaxy redshift surveys, but the bulk flows predicted by our models are broadly in agreement with most available data.

Product configuration frameworks-a survey

Abstract: The manufacturing trend toward mass customization has awakened a great interest in automatic product configuration techniques. The authors review the literature on this topic, discussing the most representative knowledge-based approaches.

Dark matter haloes within clusters

Abstract: We examine the properties of dark matter haloes within a rich galaxy cluster using a high-resolution simulation that captures the cosmological context of a cold dark matter universe. The mass and force resolution permit the resolution of 150 haloes with circular velocities larger than 80 km s−1 within the cluster virial radius of 2 Mpc (with Hubble constant H0 = 50 km s−1 Mpc−1). This enables an unprecedented study of the statistical properties of a large sample of dark matter haloes evolving in a dense environment. The cumulative fraction of mass attached to these haloes varies from close to zero per cent at 200 kpc to 13 per cent at the virial radius. Even at this resolution the overmerging problem persists; haloes that pass within 100–200 kpc of the cluster centre are tidally disrupted. Additional substructure is lost at earlier epochs within the massive progenitor haloes. The median ratio of apocentric to pericentric radii is 6:1, so that the orbital distribution is close to isotropic, circular orbits are rare and radial orbits are common. The orbits of haloes are unbiased with respect to both position within the cluster and the orbits of the smooth dark matter background, and no velocity bias is detected. The tidal radii of surviving haloes are generally well-fitted using the simple analytic prediction applied to their orbital pericentres. Haloes within clusters have higher concentrations than those in the field. Within the cluster, halo density profiles can be modified by tidal forces and individual encounters with other haloes that cause significant mass loss —‘galaxy harassment’. Mergers between haloes do not occur inside the cluster virial radius.

Song Learning, Early Nutrition and Sexual Selection in Songbirds

Abstract: SYNOPSIS. The developmental processes through which songbirds acquire their species—typical songs have been well—studied from a proximate perspective, but less attention has been given to the ultimate question of why birds learn to sing. We present a new hypothesis for the adaptive significance of song learning in songbirds, suggesting that this specialized form of vocal development provides an indicator mechanism by which females can accurately assess the quality of potential mates. This hypothesis expands on the established idea that song can provide an indicator of male quality, but it explicitly links the variation in song expression that females use to choose mates to the developmental processes through which song is acquired. How well a male sings—reflected in repertoire size or in other learned features of a male's singing behavior—provides an honest indicator of quality because the timing of song learning and, more importantly, the timing of the development of brain structures mediating learning corresponds to a period in development during which young songbirds are most likely to undergo nutritional stress. This correspondence means that song learning can provide a sensitive indicator of early developmental history in general, which in turn reflects various aspects of the phenotypic and genotypic quality of a potential mate.

Malaria in the African highlands: past, present and future.

Abstract: Many of the first European settlers in Africa sought refuge from the heat and diseases of the plains by moving to the cool and salubrious highlands. Although many of the highlands were originally malaria free, there has been a progressive rise in the incidence of the disease over the last 50 years, largely as a consequence of agroforestry development, and it has been exacerbated by scarce health resources. In these areas of fringe transmission where the malaria pattern is unstable, epidemics may be precipitated by relatively subtle climatic changes. Since there is little immunity against the disease in these communities, outbreaks can be devastating, resulting in a substantial increase in morbidity and death among both children and adults. We present here the results obtained using a mathematical model designed to identify these epidemic-prone regions in the African highlands and the differences expected to occur as a result of projected global climate change. These highlands should be recognized as an area of special concern. We further recommend that a regional modelling approach should be adopted to assess the extent and severity of this problem and help improve disease surveillance and the quality of health care delivered in this unstable ecosystem.

The Epoch of Galaxy Formation

Abstract: We use a semianalytic model of galaxy formation in hierarchical clustering theories to interpret recent data on galaxy formation and evolution, focusing primarily on the recently discovered population of Lyman-break galaxies at z 3. For a variety of cold dark matter (CDM) cosmologies, we construct mock galaxy catalogs subject to selection criteria identical to those applied to the real data. We find that the expected number of Lyman-break galaxies is very sensitive to the assumed stellar initial mass function and to the normalization of the primordial power spectrum. For reasonable choices of these and other model parameters, it is possible to reproduce the observed abundance of Lyman-break galaxies in CDM models with ?0 = 1 and ?0 < 1. The characteristic masses, circular velocities, and star formation rates of the model Lyman-break galaxies depend somewhat on the values of the cosmological parameters, but are broadly in agreement with available data. These galaxies generally form from rare peaks at high redshift, and as a result their spatial distribution is strongly biased, with a typical bias parameter of b 4 and a comoving correlation length of r0 4 h-1 Mpc. The typical sizes of these galaxies, ~0.5 h-1 kpc, are substantially smaller than those of present-day bright galaxies. In combination with data at lower redshifts, the Lyman-break galaxies can be used to trace the cosmic star formation history. We compare theoretical predictions for this history with a compilation of recent data. The observational data match the theoretical predictions reasonably well, both for the distribution of star formation rates at various redshifts and for the integrated star formation rate as a function of redshift. Most galaxies (in our models and in the data) never experience star formation rates in excess of a few solar masses per year. Our models predict that even at z = 5, the integrated star formation rate is similar to that measured locally, although less than 1% of all the stars have formed prior to this redshift. The weak dependence of the predicted star formation histories on cosmological parameters allows us to propose a fairly general interpretation of the significance of the Lyman-break galaxies as the first galaxy-sized objects that experience significant amounts of star formation. These galaxies mark the onset of the epoch of galaxy formation that continues into the present day. The basic ingredients of a consistent picture of galaxy formation may well now be in place.

Parton distributions: A New global analysis

Abstract: We present a new analysis of parton distributions of the proton. This incorporates a wide range of new data, an improved treatment of heavy flavours and a re-examination of prompt photon production. The new set (MRST) shows systematic differences from previous sets of partons which can be identified with particular features of the new data and with improvements in the analysis. We also investigate the sensitivities of the results to (i) the uncertainty in the determination of the gluon at large $x$ , (ii) the value of $\alpha_S (M_Z^2)$ and (iii) the minimum $Q^2$ cut on the data that are included in the global fit.

Recommendations for the routine sampling of diatoms for water quality assessments in Europe

Abstract: Many methods for using diatoms for routine monitoring of water quality have been developed in Europe and, in some countries, these are being used to enforce environmental legislation. In order to facilitate their wider use, particularly with respect to European Union legislation, steps are being taken to harmonize methodology. In this paper, the principles and practice of sampling are described in relation to the main habitat types encountered in Europe. Although details of methods and sampling programmes have to be tailored to particular circumstances and the overall objectives of the monitoring, a number of generalizations can be made. Where available, rocks and other hard surfaces are the preferred substrates and methods for sampling these are described. If such substrata are not available, then introduced ('artificial') substrata have many applications. Various types of introduced substrata can be used successfully, so long as some basic precautions are described. Other types of substrata such as macrophytes and macroalgae may also be useful under certain circumstances, although there is less consensus in the literature on the most appropriate methods, and of the validity of comparisons between indices computed from epiphytic and epilithic communities. When designing surveys, it is recommended that as far as possible, extremes of non-water quality factors (e.g. shade, current speed, etc) are avoided, unless these are characteristic of the system under investigation. Detailed guidelines for sampling epilithon are described. Along with the recommendations for sampling other substrata, it is hoped that these provide a framework that can be adapted to most river types in Europe.

Dark Matter Halos within Clusters

Abstract: We examine the properties of dark matter halos within a rich galaxy cluster using a high resolution simulation that captures the cosmological context of a cold dark matter universe. The mass and force resolution permit the resolution of 150 halos with circular velocities larger than 80 kms within the cluster's virial radius of 2 Mpc. This enables an unprecedented study of the statistical properties of a large sample of dark matter halos evolving in a dense environment. The cumulative fraction of mass attached to these halos varies from 0% at 200 kpc, to 13% at the virial radius. Even at this resolution the overmerging problem persists; halos that pass within 200 kpc of the cluster center are tidally disrupted. Additional substructure is lost at earlier epochs within the massive progenitor halos. The median ratio of apocentric to pericentric radii is 6:1; the orbital distribution is close to isotropic, circular orbits are rare, radial orbits are common. The orbits of halos are unbiased with respect to both position within the cluster and with the orbits of the smooth dark matter background and no velocity bias is detected. The tidal radii of surviving halos are generally well-fit using the simple analytic prediction applied to their orbital pericenters. Halos within clusters have higher concentrations than those in the field. Within the cluster, halo density profiles can be modified by tidal forces and individual encounters with other halos that cause significant mass loss - ``galaxy harassment''. Mergers between halos do not occur inside the clusters virial radius.

The Evolution of X-Ray Clusters in a Low-Density Universe

Abstract: We present results of N-body/gasdynamical simulations designed to investigate the evolution of X-ray clusters in a flat, low-density, ?-dominated cold dark matter (CDM) cosmogony. The simulations include self-gravity, pressure gradients, and hydrodynamical shocks, but neglect radiative cooling. The density profile of the dark matter component can be fitted accurately by the simple formula originally proposed by Navarro, Frenk, & White to describe the structure of clusters in a CDM universe with ? = 1. In projection, the shape of the dark matter radial density profile and the corresponding line-of-sight velocity dispersion profile are in very good agreement with the observed profiles for galaxies in the Canadian Network for Observational Cosmology sample of clusters. This suggests that galaxies are not strongly segregated relative to the dark matter in X-ray luminous clusters. The gas in our simulated clusters is less centrally concentrated than the dark matter, and its radial density profile is well described by the familiar ?-model. As a result, the average baryon fraction within the virial radius (rvir) is only 85%-90% of the universal value and is lower nearer the center. The total mass and velocity dispersion of our clusters can be accurately inferred (with ~15% uncertainty) from their X-ray emission-weighted temperature. We generalize Kaiser's scale-free scaling relations to arbitrary power spectra and low-density universes and show that simulated clusters generally follow these relations. The agreement between the simulations and the analytical results provides a convincing demonstration of the soundness of our gasdynamical numerical techniques. Although our simulated clusters resemble observed clusters in several respects, the slope of the luminosity-temperature relation implied by the scaling relations, and obeyed by the simulations, is in disagreement with observations. This suggests that nongravitational effects such as preheating or cooling must have played an important role in determining the properties of the observed X-ray emission from galaxy clusters.

A hyperluminous galaxy at z = 2.8 found in a deep submillimetre survey

Abstract: We present a detailed study of SMM 02399–0136, a hyperluminous, active galaxy selected from a submm survey of the distant Universe. This galaxy is the brightest source in the fields of six rich, lensing clusters, with a total area of 0.01 deg2, that we have mapped with a sensitivity of ∼ 2 mJy beam−1 at 850 μm. We identify a compact optical counterpart with an apparent magnitude of B ∼ 23 and a low surface-brightness companion ∼ 3 arcsec away. Our spectroscopy shows that both components have the same redshift; z = 2.803 ± 0.003. The emission line widths, FWHM ≃ 1000–1500 km s−1, and line ratios, along with the compact morphology and high luminosity (MB ≃ −24.0) of the galaxy, indicate that SMM 02399–0136 contains a rare dust-embedded, narrow-line or type-2 active galactic nucleus (AGN). The source is gravitationally lensed by the foreground cluster, amplifying its apparent luminosity by a factor of 2.5, and our detailed lens model allows us to accurately correct for this. Taking the amplification into account, we estimate that SMM 02399–0136 is intrinsically a factor of five times more luminous than IRAS F 10214+4724. Its far-infrared (FIR) and Hα luminosities and low surface-brightness radio emission are indicative of an interaction-induced starburst, and the star formation rate (SFR) could be several thousand solar masses per year. This assumes that the starburst is the dominant source of energy, but we cannot yet determine reliably the relative contributions of the starburst and the buried AGN. A dust mass of 5–7 × 108 M⊙ is indicated by our data for a dust temperature of 40–50 K, independent of the dominant energy source. We estimate the possible space density of such luminous submm sources, and find that while a large population of these obscured sources could be detected in future wide-field submm surveys, they are unlikely to dominate the faint counts in this waveband. Galaxies such as SMM 02399–0136 and F 10214+4724 cannot easily be detected in conventional AGN/QSO surveys, and so estimates of the prevalence of AGN in the early Universe may require significant revision.

Temporal and spatial patterns of biological community development at nascent deep-sea hydrothermal vents (9°50 N, East Pacific Rise)

Abstract: The April 1991 discovery of newly formed hydrothermal vents in areas of recent volcanic eruption between 9°45′N and 9°52′N on the East Pacific Rise provided a unique opportunity to follow temporal changes in biological community structure from the “birth” of numerous deep-sea hydrothermal vents. In March l992, DSV Alvin was used to deploy an on-bottom observatory, the Biologic–Geologic Transect, to monitor faunal succession along a 1.37 km segment of the axial summit caldera between 9°49.61′N and 9°50.36′N (depth ∼2520 m). Photo- and videographic documentation of megafaunal colonization and chemical analyses of diffuse hydrothermal fluids associated with many of these developing communities within the Transect were performed in March 1992, December 1993, October 1994, and November 1995. Photographic and chemical time-series analyses revealed the following sequence of events in low-temperature venting areas. (1) Immediately following the 1991 eruption, hydrogen sulfide and iron concentrations in diffuse fluids were extremely high (>1 mmol kg-1) and microbially derived material blanketed active areas of venting in the form of thick microbial mats. (2) Mobile vent fauna (e.g. amphipods, copepods, octopods, and galatheid and brachyuran crabs) and non-vent fauna (e.g. nematocarcinid shrimp) proliferated in response to this increased biological production. (3) Within 1 yr of the eruption, areal coverage of microbial mat was reduced by ∼60% and individuals of the vestimentiferan tube worm Tevnia jerichonana settled gregariously in areas where diffuse flow was most intense. (4) Two years after the eruption, maximum levels of H2S decreased by almost half (from 1.90 to 0.97 mmol kg-1) and dense thickets of the vestimentiferan Riftia pachyptila dominated vent openings previously inhabited by Tevnia jerichonana. (5) Three years after the eruption, maximum hydrogen sulfide levels declined further to 0.88 mmol kg-1 and mussels (Bathymodiolus thermophilus) were observed on basaltic substrates. (6) Four years after the eruption, galatheid crabs and serpulid polychaetes increased in abundance and were observed close to active vent openings as maximum hydrogen levels decreased to 0.72 mmol kg-1. Also by this time mussels had colonized on to tubes of Riftia pachyptila. (7) Between 3 and 5 yr after the eruption, there was a 2- to 3-fold increase in the number of species in the faunal assemblages. In the absence of additional volcanic/tectonic disturbance, we predict that mytilid and vesicomyid bivalves will gradually replace vestimentiferans as the dominant megafauna 5–10 yr following the eruption. We also anticipate that the abundance of suspension feeders will decline during this period while the abundance of carnivores will increase. We hypothesize that the above series of events (1–7) represents a general sequence of biological successional changes that will occur at newly formed low-temperature deep-sea hydrothermal vents along the northern East Pacific Rise and contiguous ridge axes. Megafaunal colonization at deep-sea hydrothermal vents is considered to be the consequence of an intimate interaction of the life-history strategies of individual species, physical oceanographic processes, and the dynamic hydrothermal environment. Our observations indicate that the successful sequential colonization of dominant megafaunal vent species, from Tevnia jerichonana to Riftia pachyptila to Bathymodiolus thermophilus, also may be strongly influenced by temporal changes in geochemical conditions. Additional evidence demonstrating the close link between diffuse vent flux, fluid geochemistry, and faunal succession included the rapid death of several newly formed biological assemblages coincident with abrupt changes in the geochemical composition of the venting fluid and the local refocusing or cessation of vent flow. These correlations suggest that future models of faunal succession at hydrothermal vents along intermediate to fast-spreading mid-ocean ridges should consider not only the interplay of species-specific life-history strategies, community productivity, and physical oceanographic processes, but also the influence of changing geochemical conditions on the sequential colonization of megafaunal species.

P3M‐SPH simulations of the Lyα forest

Abstract: We investigate the importance of several numerical artefacts such as lack of resolution on spectral properties of the Lyα forest as computed from cosmological hydrodynamic simulations in a standard cold dark matter universe. We use a new simulation code which is based on a combination of a hierarchical particle–particle–particle–mesh (P3M) scheme for gravity and smoothed particle hydrodynamics (SPH) for gas dynamics. We have performed extensive comparisons between this new code and a modified version of the HYDRA code of Couchman et al. and find excellent agreement. We have also rerun the TREESPH simulations of Hernquist et al. using our new codes and find very good agreement with their published results. This shows that results from hydrodynamical simulations that include cooling are reproducible with different numerical algorithms. We then use our new code to investigate several numerical effects, such as resolution, on spectral statistics deduced from Voigt profile fitting of lines by running simulations with gas particle masses of 1.4 × 108, 1.8 × 107, 2.2 × 106 and 2.1 × 105 M⊙. When we increase the numerical resolution the mean effective hydrogen optical depth converges and so does the column density distribution. However, higher resolution simulations produce narrower lines and consequently the b parameter (velocity width) distribution has only marginally converged in our highest resolution run. Obtaining numerical convergence for the mean He II transmission is demanding. When progressively smaller haloes are resolved at better resolution, a larger fraction of low-density gas contracts to moderate overdensities in which He ii is already optically thick, and this increases the net transmission, making it difficult to simulate He ii reliably. Our highest resolution simulation gives a mean effective optical depth in He ii 5 per cent lower than the simulation with eight times lower mass resolution, illustrating the degree to which the He ii optical depth has converged. In contrast, the hydrogen mean optical depth for these runs is identical. As many properties of the simulated Lyα forest depend on resolution, one should be careful when deducing physical parameters from a comparison of the simulated forest with the observed one. We compare predictions from our highest resolution simulation in a cold dark matter universe, with a photoionizing background inferred from quasars as computed by Haardt &38; Madau, with observations. The simulation reproduces both the H I column density and b parameter distribution when we assume a high baryon density, ΩB h2 ≳ 0.028. In addition we need to impose a higher intergalactic medium (IGM) temperature than predicted within our basic set of assumptions. We argue that such a higher temperature could be caused by differences between the assumed and true reionization history. The simulated H I optical depth is in good agreement with observations, but the He ii optical depth is lower than observed. Fitting the He ii optical depth requires a larger jump, ∼ 14, between the photon flux at the H I and He ii edge than is present in the Haardt &38; Madau spectrum.

Post-dispersal seed predation: consequences for plant demography and evolution

Abstract: Post-dispersal seed predation is only one of many factors underlying plant demography and evolution. Nevertheless, the generalist feeding habits of many post-dispersal seed predators and the limited ability of plants either to compensate for or to respond to post-dispersal seed losses directly suggest that post-dispersal seed predation may have a considerable impact on plant populations. Seed predators probably have little direct influence on the demography of plants that regenerate exclusively by vegetative means or are buffered by a large active seed bank, but such species are only a minority in most plant communities. In general, ants are significant post-dispersal seed predators in arid and semi-arid ecosystems while they act mainly as seed dispersers rather than as predators in temperate ecosystems. Although studies have probably underestimated the importance of invertebrates and birds as seed predators, rodents appear to have greater potential to influence seed dynamics, and are particularly important in temperate ecosystems. For example, production of mast seed crops is more effective at satiating specialist invertebrate seed predators than generalist vertebrates, and recruitment may be limited by post-dispersal seed predation even during mast years. Both spatial variation in post-dispersal seed predation and differences in predation between species are important elements which facilitate the coexistence of different plant species. Where microsites are limiting, selective post-dispersal seed predators can influence pre-emptive competition for these microsites. Seed size determines the extent of density-dependent predation and the exploitation of buried seed. This suggests that post-dispersal seed predators may also play a role in the evolution of seed characteristics. However, conclusions regarding the ecological and evolutionary impact of post-dispersal seed predators will remain speculative without a more substantial empirical base.

Structural, Magnetic, and Photomagnetic Studies of a Mononuclear Iron(II) Derivative Exhibiting an Exceptionally Abrupt Spin Transition. Light-Induced Thermal Hysteresis Phenomenon.

Abstract: The new spin-crossover compound Fe(PM-BiA)2(NCS)2 with PM-BiA = N-(2-pyridylmethylene)aminobiphenyl has been synthesized. The temperature dependence of χMT (χM = molar magnetic susceptibility and T...

P3M-SPH simulations of the Lyman-alpha Forest

Abstract: (Abridged) We investigate the importance of several numerical artifacts such as lack of resolution on spectral properties of the Lyman alpha forest as computed from cosmological hydrodynamic simulations in a standard cold dark matter universe. We assume an ionising background produced by quasars as computed by Haardt & Madau. We use a new simulation code based on P3M and SPH, which we compare in detail with a modified version of HYDRA (Couchman et al.) and published results of TREESPH (Hernquist et al.). The agreement is very good between all three codes. We then use our new code to investigate several numerical effects such as resolution on spectral statistics deduced from Voigt profile fitting. Our highest resolution simulation has a mass resolution of 2.1x10^5 solar masses. The column density distribution is converged but the b-parameter distribution is only marginally converged. The simulation reproduces both the HI column density and b-parameter distribution when we assume a high baryon density, Omega_B h^2 > 0.028. In addition we need to impose a higher IGM temperature than predicted within our basic set of assumptions. The simulated HI optical depth is in good agreement with observations but the HeII optical depth is lower than observed. Fitting the latter requires a larger jump between the photon flux at the H and He edge than is present in the Haardt & Madau spectrum.