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Number Density (number + density)
Selected AbstractsPetrography of refractory inclusions in CM2.6 QUE 97990 and the origin of melilite-free spinel inclusions in CM chondritesMETEORITICS & PLANETARY SCIENCE, Issue 10 2007Alan E. Rubin It contains 1.8 vol% refractory inclusions; 40 were studied from a single thin section. Inclusion varieties include simple, banded and nodular structures as well as simple and complex distended objects. The inclusions range in mean size from 30 to 530 ,m and average 130 ± 90 ,m. Many inclusions contain 25 ± 15 vol% phyllosilicate (predominantly Mg-Fe serpentine); several contain small grains of perovskite. In addition to phyllosilicate, the most abundant inclusions in QUE 97990 consist mainly of spinel-pyroxene (35%), followed by spinel (20%), spinel-pyroxene-olivine (18%), pyroxene (12%), pyroxene-olivine (8%) and hibonite ± spinel (8%). Four pyroxene phases occur: diopside, Al-rich diopside (with , 8.0 wt% Al2O3), Al-Ti diopside (i.e., fassaite), and (in two inclusions) enstatite. No inclusions contain melilite. Aqueous alteration of refractory inclusions transforms some phases (particularly melilite) into phyllosilicate; some inclusions broke apart during alteration. Melilite-free, phyllosilicate-bearing, spinel inclusions probably formed from pristine, phyllosilicate-free inclusions containing both melilite and spinel. Sixty-five percent of the refractory inclusions in QUE 97990 appear to be largely intact; the major exception is the group of spinel inclusions, all of which are fragments. Whereas QUE 97990 contains about 50 largely intact refractory inclusions/cm2, estimates from literature data imply that more-altered CM chondrites have lower modal abundances (and lower number densities) of refractory inclusions: Mighei (CM , 2.3) contains roughly 0.3,0.6 vol% inclusions (,10 largely intact inclusions/cm2); Cold Bokkeveld (CM2.2) contains ,0.01 vol% inclusions (on the order of 6 largely intact inclusions/cm2). [source] The scale size of chondrule formation regions: Constraints imposed by chondrule cooling ratesMETEORITICS & PLANETARY SCIENCE, Issue 12 2001Lon L. Hood The presence of fine-grained rims around chondrules in most unequilibrated chondrites also indicates that a significant quantity of micron-sized dust was present in chondrule formation regions. Here, we assume that the persistent external energy source needed to explain chondrule cooling rates consists primarily of radiation from surrounding heated chondrules, fine dust, and gas after the formation event. Using an approximate one-dimensional numerical model for the outward diffusion of thermal radiation from such a system, the scale sizes of formation regions required to yield acceptable cooling rates are determined for a range of possible chondrule, dust, and gas parameters. Results show that the inferred scale sizes depend sensitively on the number densities of micron-sized dust and on their adopted optical properties. In the absence of dust, scale sizes > 1000 km are required for plausible maximum chondrule number densities and heated gas parameters. In the presence of dust with mass densities comparable to those of the chondrules and with absorptivities and emissivities of ,0.01 calculated for Mie spheres with a pure mineral composition, scale sizes as small as ,100 km are possible. If dust absorptivities and emissivities approach unity (as may occur for particles with more realistic shapes and compositions), then scale sizes as small as ×10 km are possible. Considering all uncertainties in model parameters, it is concluded that small scale sizes (10,100 km) for chondrule formation regions are allowed by the experimentally inferred cooling rates. [source] Fluorescence resonance energy transfer and anisotropy reveals both hetero- and homo-energy transfer in the pleckstrin homology-domain and the parathyroid hormone-receptorMICROSCOPY RESEARCH AND TECHNIQUE, Issue 1 2009Ralf Steinmeyer Abstract We present a method and an apparatus of polarized fluorescence resonance energy transfer (FRET) and anisotropy imaging microscopy done in parallel for improved interpretation of the photophysical interactions. We demonstrate this apparatus to better determine the protein,protein interactions in the pleckstrin homology domain and the conformational changes in the Parathyroid Hormone Receptor, a G-protein coupled receptor, both fused to the cyan and yellow fluorescent proteins for either inter- or intramolecular FRET. In both cases, the expression levels of proteins and also background autofluorescence played a significant role in the depolarization values measured in association with FRET. The system has the sensitivity and low-noise capability of single-fluorophore detection. Using counting procedures from single-molecule methods, control experiments were performed to determine number densities of green fluorescence protein variants CFP and YFP where homo resonance energy transfer can occur. Depolarization values were also determined for flavins, a common molecule of cellular background autofluorescence. From the anisotropy measurements of donor and acceptor, the latter when directly excited or when excited by energy transfer, we find that our instrumentation and method also characterizes crucial effects from homotransfer, polarization specific photobleaching and background molecules. Microsc. Res. Tech., 2009. © 2008 Wiley-Liss, Inc. [source] A fast computation of the secondary ion production in the ionosphere of MarsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2009William P. Nicholson ABSTRACT We present an analytic method for the rapid computation of secondary ion and electron production due to electron impact as suprathermal electrons produced by primary photoproduction propagate through the neutral background Martian atmosphere. We use a one-dimensional kinetic model, Trans -Mars, that solves a stationary Boltzmann transport equation to describe the ionosphere of Mars with the neutral background atmosphere (temperatures, number densities and geopotential heights) provided by a three-dimensional global circulation model, MarTIM. Parameters are given to allow the rapid computation of secondary ion production for 11 ion species (CO+2, CO++2, CO+, C+, N+2, N++2, N+, O+2, O++2, O+, O++) as well as for the secondary electron production. We use the neutral global circulation model to show that while the efficiency (,) of ion and electron production (ratio of secondary to primary production) does vary with solar zenith angle it can be parametrized with a simple function, which is given. We also show that variations with solar cycle and solar longitude are negligible about the region of the primary and secondary production peaks. [source] Stellar haloes and elliptical galaxy formation: origin of dynamical properties of the planetary nebula systemsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Kenji Bekki ABSTRACT Recent spectroscopic observations of planetary nebulae (PNe) in several elliptical galaxies have revealed structural and kinematical properties of the outer stellar halo regions. In order to elucidate the origin of the properties of these planetary nebula systems (PNSs), we consider the merger scenario in which an elliptical galaxy is formed by merging of spiral galaxies. Using numerical simulations, we particularly investigate radial profiles of projected PN number densities, rotational velocities and velocity dispersions of PNSs extending to the outer halo regions of elliptical galaxies formed from major and unequal-mass merging. We find that the radial profiles of the project number densities can be fitted to the power law and the mean number density in the outer haloes of the ellipticals can be more than an order of magnitude higher than that of the original spiral's halo. The PNSs are found to show a significant amount of rotation (V/, > 0.5) in the outer halo regions (R > 5Re) of the ellipticals. Two-dimensional velocity fields of PNSs are derived from the simulations and their dependences on model parameters of galaxy merging are discussed in detail. We compare the simulated kinematics of PNSs with that of the PNS observed in NGC 5128 and thereby discuss advantages and disadvantages of the merger model in explaining the observed kinematics of the PNS. We also find that the kinematics of PNSs in elliptical galaxies are quite diverse depending on the orbital configurations of galaxy merging, the mass ratio of merger progenitor spirals and the viewing angle of the galaxies. This variation translates directly into possible biases by a factor of 2 in observational mass estimation. However, the biases in the total mass estimates can be even larger. The best case systems viewed edge-on can appear to have masses lower than their true mass by a factor of 5, which suggests that current observational studies on PN kinematics of elliptical galaxies can significantly underestimate their real masses. [source] Simulations of the heating of the Galactic stellar discMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002Jyrki Hänninen ABSTRACT The velocity dispersion of nearby stars in the Galactic disc is well known to increase substantially with age; this is the so-called age,velocity relation, and is interpreted as a ,heating' of the disc as a function of time. We have studied the heating of the Galactic stellar disc caused by giant molecular clouds and halo black holes, via simulations of the orbits of tracer stars embedded in a patch of the local Galactic disc. We examine a range of masses and number densities of the giant molecular cloud and halo black hole perturbers. The heating of the stellar disc in the simulations is fitted with a simple power law of the form ,,t,, where , is the velocity dispersion of the tracer stars as a function of time, t. We also fit this form to the best determinations of the increase in the velocity dispersion as a function of time as derived from stars in the solar neighbourhood for which ages can be reliably assigned. Observationally, , is found to lie in the range 0.3,0.6, i.e. it remains poorly constrained and its determination is probably still dominated by systematic errors. Better constrained observationally is the ratio of the velocity dispersions of the stars in the vertical z and horizontal x directions (i.e. towards the Galactic Centre), ,z/,x= 0.5 ± 0.1. For the heating of the stellar disc caused by giant molecular clouds (GMCs) we derive a heating ,,t0.21, which differs somewhat from early (analytic) studies in which ,,t1/4. This confirms the well-known results that there are insufficient GMCs to heat the Galactic disc appropriately. A range of dark halo black hole scenarios are verified to heat the stellar disc as ,,t1/2 (as expected from analytical studies), and give ,z/,x in the range 0.5,0.6, which is consistent with observations. Black holes with a mass of 107 M, are our favoured disc heaters, although they are only marginally consistent with observations. Simulations featuring a combination of giant molecular clouds and halo black holes can explain the observed heating of the stellar disc, but since other perturbing mechanisms, such as spiral arms, are yet to be included, we regard this solution as being ad hoc. [source] Numerical simulations of photon trapping in doped photonic crystals doped with multi-level atomsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2005Mahi R. Singh Abstract A theory of photon trapping has been developed in photonic band-gap (PBG) and dispersive polaritonic band-gap (DPBG) materials doped with an ensemble of five-level atoms. These materials have gaps in their photon energy spectra. The atoms are prepared as coherent superpositions of the two lower states and interact with a reservoir and two photon fields. They also interact with each other by dipole-dipole interaction. The Schrödinger equation and the Laplace transform method are used to calculate the expressions for the number densities of the atomic states. Numerical simulations for a PBG material reveal that when the resonance energies lie away from the band edges and within the lower or upper bands, trapping is observed at certain values of the relative Rabi frequency associated with the two fields, which vary depending on the strength of the dipole-dipole interaction between the atoms. Also, if the photon fields are held constant, the population densities of the excited states of the atoms increase with increasing dipole-dipole interaction. These are very interesting phenomena. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fatigue behaviour of SiCp -reinforced aluminium composites in the very high cycle regime using ultrasonic fatigueFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2006J. HUANG ABSTRACT The fatigue behaviour of a 2009/SiC/15p-T4 DRA composite has been examined in the very high cycle fatigue (VHCF) regime where 107,Nf, 109 cycles. Ultrasonic fatigue was used to achieve the very high cycle counts. Careful processing yielded a composite with a very homogeneous particle distribution with minimal clustering. Fatigue crack initiation was observed almost exclusively at AlCuFe inclusions with no crack initiation observed at SiC particle clusters. Fatigue lives at a given stress level exhibited minimal scatter and subsurface crack initiation was observed in all cases. This behaviour is consistent with the presence of a low number density of critical inclusions that are responsible for crack initiation very early in fatigue life. [source] Scattering of elastic waves in media with a random distribution of fluid-filled cavities: theory and numerical modellingGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004Tae-Kyung Hong SUMMARY The propagation of elastic waves is modelled in media with a random distribution of fluid-filled circular cavities, which display high physical impedance in contrast to background media. Theoretical attenuation expressions for media with circular cavities, which may be filled with any material (e.g. vacuum, fluid, elastic materials), are formulated using an ensemble treatment for first-order transmitted waves. Numerical estimates of scattering attenuation rates agree with the theoretical results well. The scattering attenuations (Q,1) are proportional to the scale of cavities and the number density (,, number of cavities per area in a medium). The decrease of primary energy with the size of cavities does not result in the increase of coda energy owing to the increase of both purely backscattered waves from cavities and the trapped waves inside cavities. Scattering properties (e.g. scattering attenuation, coda energy, phase fluctuation of primary waves) in media with randomly distributed cavities are very different from those in stochastic random media. It appears that heterogeneities with high impedance in the earth may not be well represented with stochastic random heterogeneities. [source] Effective-medium theories for fluid-saturated materials with aligned cracksGEOPHYSICAL PROSPECTING, Issue 5 2001J.A. Hudson There is general agreement between different theories giving expressions for the overall properties of materials with dry, aligned cracks if the number density of cracks is small. There is also very fair agreement for fluid-filled isolated cracks. However, there are considerable differences between two separate theories for fluid-filled cracks with equant porosity. Comparison with recently published experimental data on synthetic sandstones gives a good fit with theory for dry samples. However, although the crack number density in the laboratory sample is such that first-order theory is unlikely to apply, expressions correct to second order (in the number density) provide a worse fit. It also appears that the ratio of wavelength to crack size is not sufficiently great for any detailed comparison with effective-medium theories, which are valid only when this ratio is large. The data show dispersion effects for dry cracks and scattering, neither of which will occur at sufficiently long wavelengths. Data from the water-saturated samples indicate that the effect of equant porosity is significant, although the two theories differ strongly as to just how significant. Once again, and in spite of the reservations mentioned above, a reasonable fit between theory and observation can be shown. [source] Supramolecular Self-Assembled Dendritic Nonlinear Optical Chromophores: Fine-Tuning of Arene,Perfluoroarene Interactions for Ultralarge Electro-Optic Activity and Enhanced Thermal StabilityADVANCED MATERIALS, Issue 19 2009Xing-Hua Zhou Unprecedented electro-optic (EO) activity and excellent alignment stability at 85,°C are demonstrated through rational design of a new series of dendronized polyenic chromophores capable of supramolecular self-assembly directed by fine-tuned arene,perfluoroarene interactions. Analysis of the EO properties showed exceptional poling efficiency for these molecular glasses at high chromophore number density. [source] Routes to Grow Well-Aligned Arrays of ZnSe Nanowires and Nanorods,ADVANCED MATERIALS, Issue 11 2005X. Zhang Well-aligned ZnSe nanowires and nanorods can be grown on ZnSe epilayers on different GaAs substrates, with and without catalyst, by metal,organic chemical vapor deposition. Gold particles affect the number density, growth direction, and the morphology of the resulting nanostructures. In the absence of the gold catalyst, hexagonal nanorods grow along the <111> directions (see Figure). Growth defects on the epilayers may be the nucleation sites of the nanorods. [source] MECHANICAL,ACOUSTIC AND SENSORY EVALUATIONS OF CORNSTARCH,WHEY PROTEIN ISOLATE EXTRUDATESJOURNAL OF TEXTURE STUDIES, Issue 4 2007E.M. CHENG ABSTRACT The mechanism relating sensory perception of brittle food foams to their mechanical and acoustic properties during crushing was investigated. Cornstarch was extruded with four levels of whey protein isolate (0, 6, 12 and 18%) and two levels of in-barrel moisture (23 and 27%). Hardness, fracturability and roughness of mass were three main sensory attributes that varied substantially between products. High correlations (r = 0.841,0.998) were observed between sensory attributes and instrumentally determined mechanical properties, including crushing force (11.2,57.9 N) and crispness work (4.6,75.8 N·mm). Based on acoustic data obtained during instrumental crushing, time-domain signal processing and a novel voice recognition technique utilizing frequency spectrograms were successfully employed for understanding the differences in the sensory properties of various products. Microstructure features, including average cell diameter (1.00,2.94 mm), average wall thickness (0.04,0.27 mm) and cell number density (7,193 cell/cm3), were characterized noninvasively using X-ray microtomography, and proved to be critical in relating sensory perception of the cellular extrudates to their mechanical,acoustic signatures. PRACTICAL APPLICATIONS The sensory perception of crispy and crunchy food products is primarily a function of their mechanical response and emission of sounds during fracture. The current study was focused on understanding these relationships in the context of brittle extruded foods. The mechanical,acoustic techniques outlined in this study have the potential of reducing the time, costs and subjectivity involved in evaluation of new foods by human panels, and can be a useful tool in the overall product development cycle. These techniques need not be limited only to food systems, as properties of any rigid, fracturable material can be characterized based on its mechanical,acoustic signature. [source] Abnormal Grain Growth in Alumina with Anorthite Liquid and the Effect of MgO AdditionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2002Chan Woo Park Abnormal grain growth (AGG) in alumina with anorthite liquid has been observed with varying anorthite and MgO contents, at 1620°C. When only anorthite is added to form a liquid matrix, the grain,liquid interfaces have either flat or hill-and-valley shapes indicating atomically flat (singular) structures. The large grains grow at accelerated rates to produce AGG structures with large grains elongated along their basal planes. This is consistent with the slow growth at low driving forces and accelerated growth above a critical driving force predicted by the two-dimensional nucleation theory of surface steps. With increasing temperature, the AGG rate increases. The number density of the abnormally large grains increases with increasing anorthite content. The addition of MgO causes some grain,liquid interfaces to become curved and hence atomically rough. The grains also become nearly equiaxed. With increasing MgO content the number density of the abnormally large grains increases until the grain growth resembles normal growth. This result is qualitatively consistent with the decreasing surface step free energy associated with partial interface roughening transition. [source] Effect of Seeding on the Microstructure and Mechanical Properties of ,-SiAlON: I, Y-SiAlONJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2002Misha Zenotchkine The effect of seeding on the microstructure and mechanical properties of single-phase Y-,-SiAlON ceramics with elongated grains has been studied. Seeds of the intended ,-SiAlON compositions but with different size, shape, and number of grains have been compared for their effects. The microstructure, resistance (R-curve) behavior, and Weibull modulus are strongly correlated to the number density of the seeds. The highest fracture toughness reached is ,12 MPa·m1/2 and can be obtained with as little as 1% seeding. The thermodynamic stability of seeds has been examined and is attributed to their chemical composition. [source] Effect of the Growth Treatment on Two-Stage Nucleation ExperimentsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2001Mark J. Davis Numerical simulations are presented that document the strong effect of a previously underappreciated portion of two-stage thermal treatments used in the study of nucleation processes: the "heat-up" process whereby samples are heated from "nucleation" conditions to "growth" conditions. The simulations indicate that two limiting regimes exist, dependent on (a) the cluster size distribution of as-quenched glasses, (b) the temperatures used for nucleation and growth, and (c) the rates of heating and cooling: (1) all clusters larger than the critical size at growth conditions (n*gr) will grow to macroscopic size (the "standard" case); and (2) all clusters larger than the critical size at nucleation conditions (n*nuc) will grow to macroscopic size. In addition, cases in which the "effective critical size" (n*eff) is intermediate between n*gr and n*nuc can also occur. Cases in which n*eff < n*gr is manifested during nucleation experiments as an abrupt boost in crystal number density during the heat-up from nucleation to growth conditions, as all clusters larger than n*eff are rapidly "flushed" past n*gr. For the system studied herein, this can lead to a 106 -fold increase in final number density within seconds to a few minutes. Finally, the importance of structural relaxation for this process is demonstrated by examining a case in which the nucleation temperature is below the nominal glass transition temperature. [source] Cationic and Anionic Conjugated Polyelectrolytes: Aggregation-Mediated Fluorescence Energy Transfer to Dye-Labeled DNAMACROMOLECULAR RAPID COMMUNICATIONS, Issue 16 2008Youngeup Jin Abstract An electrostatic complex of water-soluble conjugated polyelectrolytes (CPs) between anionic poly(9,9-bis(4,-sulfonatobutyl)fluorene- co-alt -1,4-phenylene) disodium salt (a-PFP) and cationic poly(9,9-bis((6,- N,N,N,-trimethylammonium)hexyl)fluorene- co -2,1,3-bezothiadiazole) dibromide (85:15) (c-PFB15) was tested as a fluorescence resonance energy transfer (FRET) donor to Texas Red (TR)-labeled single-stranded DNA (ssDNA-TR) via two-step FRET processes. Electrostatic complexation of a-PFP and c-PFB15 in water leads to aggregation of polymer chains, a concomitant reduction of intersegment distances, and energy transfer to the benzothiadiazole (BT) segments. The following complexation with ssDNA-TR leads to energy transfer from BT to TR via two-step FRET processes. This detection schematic shows an FRET-induced signal amplification, which can be achieved by adjusting the charge ratio in the cationic/anionic CP complex and controlling the number density of the binding CPs around the acceptor, resulting in enhanced antenna effects and sensitivity in CP-based FRET DNA detection assays. [source] Identification of the boundary surface of an interstellar cloud from a measurement of the photon far-fieldMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 6 2004A. Belleni-Morante Abstract We study an inverse problem for photon transport in a host medium (e.g. an interstellar cloud), that occupies a bounded and strictly convex region ,,R3. Under the assumption that the cross-sections and the sources are known, we identify the boundary surface , = ,,(within a suitable family F of surfaces), provided that one value of the photon number density is measured at some given location far from ,. Copyright © 2004 John Wiley & Sons, Ltd. [source] A mathematical model for a spatial predator,prey interactionMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 11 2002Annunziata Palumbo A predator,prey model is proposed within the general scheme of extended thermodynamics. An additional equation of balance is needed to account for the flux of the number density of the predator as an independent field variable. Copyright © 2002 John Wiley & Sons, Ltd. [source] The nature of the Sloan Digital Sky Survey galaxies in various classes based on morphology, colour and spectral features , III.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010Environments ABSTRACT We present a study on the environments of the Sloan Digital Sky Survey (SDSS) galaxies divided into fine classes based on their morphology, colour and spectral features. The SDSS galaxies are classified into early-type and late-type; red and blue; passive, H ii, Seyfert and low-ionization nuclear emission-line region (LINER), which returns a total of 16 fine classes of galaxies. We estimate the local number density, target-excluded local luminosity density, local colour, close pair fraction and the luminosity and colour of the brightest neighbour, which are compared between the fine classes comprehensively. The morphology,colour class of galaxies strongly depends on the local density, with the approximate order of high-density preference: red early-type galaxies (REGs); red late-type galaxies (RLGs); blue early-type galaxies (BEGs) and blue late-type galaxies (BLGs). We find that high-density environments (like cluster environments) seem to suppress active galactic nucleus activity. The pair fraction of H ii REGs does not show a statistically significant difference from that of passive REGs, while the pair fraction of H ii BLGs is smaller than that of non-H ii BLGs. H ii BLGs show obvious double (red + blue) peaks in the distribution of the brightest neighbour colour, while red galaxies show a single red peak. The brightest neighbours of Seyfert BLGs tend to be blue, while those of LINER BLGs tend to be red, which implies that the difference between Seyfert and LINER may be related to the pair interaction. Other various environments of the fine classes are investigated, and their implications for galaxy evolution are discussed. [source] Bayesian galaxy shape measurement for weak lensing surveys , II.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Application to simulations ABSTRACT In this paper, we extend the Bayesian model fitting shape measurement method presented in Miller et al., and use the method to estimate the shear from the Shear TEsting Programme simulations (STEP). The method uses a fast model fitting algorithm that uses realistic galaxy profiles and analytically marginalizes over the position and amplitude of the model by doing the model fitting in Fourier space. This is used to find the full posterior probability in ellipticity. The shear is then estimated in a Bayesian way from this posterior probability surface. The Bayesian estimation allows measurement bias arising from the presence of random noise to be removed. In this paper, we introduce an iterative algorithm that can be used to estimate the intrinsic ellipticity prior and show that this is accurate and stable. We present results using the STEP parametrization that relates the input shear ,T to the estimated shear ,M by introducing a bias m and an offset c: ,M,,T=m,T+c. The average number density of galaxies used in the STEP1 analysis was 9 per square arcminute, for STEP2 the number density was 30 per square arcminute. By using the method to estimate the shear from the STEP1 simulations we find the method to have a shear bias of m= 0.006 ± 0.005 and a variation in shear offset with point spread function type of ,c= 0.0002. Using the method to estimate the shear from the STEP2 simulations we find that the shear bias and offset are m= 0.002 ± 0.016 and c=,0.0007 ± 0.0006, respectively. In addition, we find that the bias and offset are stable to changes in the magnitude and size of the galaxies. Such biases should yield any cosmological constraints from future weak lensing surveys robust to systematic effects in shape measurement. Finally, we present an alternative to the STEP parametrization by using a quality factor that relates the intrinsic shear variance in a simulation to the variance in shear that is measured and show that the method presented has an average of Q, 100 which is at least a factor of 10 times better than other shape measurement methods. [source] The evolution of submillimetre galaxies: two populations and a redshift cut-offMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2008J. V. Wall ABSTRACT We explore the epoch dependence of number density and star formation rate for submillimetre galaxies (SMGs) found at 850 ,m. The study uses a sample of 38 SMG in the Great Observatories Origins Deep Survey (GOODS)-N field, for which cross-waveband identifications have been obtained for 35/38 members together with redshift measurements or estimates. A maximum-likelihood analysis is employed, along with the ,single-source-survey' technique. We find a diminution in both space-density and star formation rate at z > 3, closely mimicking the redshift cut-offs found for quasi-stellar objects (QSOs) selected in different wavebands. The diminution in redshift is particularly marked at a significance level too small to measure. The data further suggest, at a significance level of about 0.001, that two separately evolving populations may be present, with distinct luminosity functions. These results parallel the different evolutionary behaviours of Luminous Infrared Galaxies and Ultra-Luminous Infrared Galaxies, and represent another manifestation of ,cosmic down-sizing', suggesting that differential evolution extends to the most extreme star-forming galaxies. [source] The properties of galaxies in voidsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Santiago G. Patiri ABSTRACT We present a comparison of the properties of galaxies in the most underdense regions of the Universe, where the galaxy number density is less than 10 per cent of the mean density, with galaxies from more typical regions. We have compiled a sample of galaxies in 46 large nearby voids that were identified using the Sloan Digital Sky Survey DR4, which provides the largest coverage of the sky. We study the u,r colour distribution, morphology, specific star formation rate (SFR) and radial number density profiles for a total of 495 galaxies fainter than Mr=,20.4 + 5 log h located inside the voids and compare these properties with a control sample of field galaxies. We show that there is an excess of blue galaxies inside the voids. However, inspecting the properties of blue and red galaxies separately, we find that galaxy properties such as colour distribution, bulge-to-total ratios and concentrations are remarkably similar between the void and overall sample. The void galaxies also show the same specific SFR at fixed colour as the control galaxies. We compare our results with the predictions of cosmological simulations of galaxy formation using the Millennium Run semi-analytic galaxy catalogue. We show that the properties of the simulated galaxies in large voids are in reasonably good agreement with those found in similar environments in the real Universe. To summarize, in spite of the fact that galaxies in voids live in the least dense large-scale environment, this environment makes very little impact on the properties of galaxies. [source] Stellar haloes and elliptical galaxy formation: origin of dynamical properties of the planetary nebula systemsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Kenji Bekki ABSTRACT Recent spectroscopic observations of planetary nebulae (PNe) in several elliptical galaxies have revealed structural and kinematical properties of the outer stellar halo regions. In order to elucidate the origin of the properties of these planetary nebula systems (PNSs), we consider the merger scenario in which an elliptical galaxy is formed by merging of spiral galaxies. Using numerical simulations, we particularly investigate radial profiles of projected PN number densities, rotational velocities and velocity dispersions of PNSs extending to the outer halo regions of elliptical galaxies formed from major and unequal-mass merging. We find that the radial profiles of the project number densities can be fitted to the power law and the mean number density in the outer haloes of the ellipticals can be more than an order of magnitude higher than that of the original spiral's halo. The PNSs are found to show a significant amount of rotation (V/, > 0.5) in the outer halo regions (R > 5Re) of the ellipticals. Two-dimensional velocity fields of PNSs are derived from the simulations and their dependences on model parameters of galaxy merging are discussed in detail. We compare the simulated kinematics of PNSs with that of the PNS observed in NGC 5128 and thereby discuss advantages and disadvantages of the merger model in explaining the observed kinematics of the PNS. We also find that the kinematics of PNSs in elliptical galaxies are quite diverse depending on the orbital configurations of galaxy merging, the mass ratio of merger progenitor spirals and the viewing angle of the galaxies. This variation translates directly into possible biases by a factor of 2 in observational mass estimation. However, the biases in the total mass estimates can be even larger. The best case systems viewed edge-on can appear to have masses lower than their true mass by a factor of 5, which suggests that current observational studies on PN kinematics of elliptical galaxies can significantly underestimate their real masses. [source] Cosmic evolution of metal densities: the enrichment of the intergalactic mediumMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006F. Calura ABSTRACT By means of chemo-photometric models for galaxies of different morphological types, we have carried out a detailed study of the history of element production by spheroidal and dwarf irregular galaxies. Spheroidal galaxies suffer a strong and intense star formation episode at early times. In dwarf irregulars, the star formation rate (SFR) proceeds at a low regime but continuously. Both galactic types enrich the intergalactic medium (IGM) with metals by means of galactic winds. We have assumed that the galaxy number density is fixed and normalized to the value of the optical luminosity function observed in the local Universe. Our models allow us to investigate in detail how the metal fractions locked up in stars in spheroids and dwarf irregulars, those present in the interstellar medium (ISM) and those ejected into the IGM have changed with cosmic time. By relaxing the instantaneous recycling approximation and taking into account stellar lifetimes, for the first time we have studied the evolution of the chemical abundance ratios in the IGM and compared our predictions with a set of observations by various authors. Our results indicate that the bulk of the IGM enrichment is due to spheroids, with dwarf irregular galaxies playing a negligible role. Our predictions grossly account for the [O/H] observed in the IGM at high redshift, but overestimate the [C/H]. Furthermore, it appears hard to reproduce the abundance ratios observed in the high-redshift IGM. Some possible explanations are discussed in the text. This is the first attempt to study the abundance ratios in the IGM by means of detailed chemical evolution models which take into account the stellar lifetimes. Numerical simulations adopting our chemical evolution prescriptions could be useful to improve our understanding of the IGM chemical enrichment. [source] A two-dimensional electrodynamical outer gap model for ,-ray pulsars: ,-ray spectrumMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006J. Takata ABSTRACT A two-dimensional electrodynamical model is used to study particle acceleration in the outer magnetosphere of a pulsar. The charge depletion from the Goldreich,Julian charge density causes a large electric field along the magnetic field lines. The charge particles are accelerated by the electric field and emit ,-rays via the curvature process. Some of the emitted ,-rays may collide with X-ray photons to make new pairs, which are accelerated again on the different field lines and emit ,-rays. We simulate the pair creation cascade in the meridional plane using the pair creation mean-free path, in which the X-ray photon number density is proportional to the inverse square of the radial distance. With the space charge density determined by the pair creation simulation, we solve the electric structure of the outer gap in the meridional plane and calculate the curvature spectrum. We investigate in detail the relation between the spectrum and total current, which is carried by the particles produced in the gap and/or injected at the boundaries of the gap. We demonstrate that the hardness of the spectrum is strongly controlled by the current carriers. Especially, the spectrum sharply softens if we assume a larger particle injection at the outer boundary of the outer gap. This is because the mean-free path of the pair creation of the inwardly propagating ,-ray photons is much shorter than the light radius, so many pairs are produced in the gap to quench the outer gap. Because the two-dimensional model can link both gap width along the magnetic field line and trans-field thickness with the spectral cut-off energy and flux, we can diagnose both the current through the gap and the inclination angle between the rotational and magnetic axes. We apply the theory to the Vela pulsar. By comparing the results with the Energetic Gamma Ray Experiment Telescope (EGRET) data, we rule out any cases that have a large particle injection at the outer boundary. We also suggest the inclination angle of ,inc, 65°. The present model predicts the outer gap starting from near the conventional null charge surface for the Vela pulsar. [source] Radial distribution and strong lensing statistics of satellite galaxies and substructure using high-resolution ,CDM hydrodynamical simulationsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Andrea V. Macciò ABSTRACT We analyse the number density and radial distribution of substructures and satellite galaxies using cosmological simulations that follow the gas dynamics of a baryonic component, including shock heating, radiative cooling and star formation within the hierarchical concordance Lambda cold dark matter model. We find that the dissipation of the baryons greatly enhances the survival of subhaloes, especially in the galaxy core, resulting in a radial distribution of satellite galaxies that closely follows the overall mass distribution. Hydrodynamical simulations are necessary to resolve the adiabatic contraction and dense cores of galaxies, resulting in a total number of satellites a factor of 2 larger than that found in pure dark matter simulation, in good agreement with the observed spatial distribution of satellite galaxies within galaxies and clusters. Convergence tests show that the cored distribution found by previous authors in pure N -body simulations was due to the physical overmerging of dark matter only structures. We proceed to use a ray-shooting technique in order to study the impact of these additional substructures on the number of violations of the cusp caustic magnification relation. We develop a new approach to try to disentangle the effect of substructures from the intrinsic discreteness of N -body simulations. Even with the increased number of substructures in the centres of galaxies, we are not able to reproduce the observed high numbers of discrepancies observed in the flux ratios of multiply lensed quasars. [source] Supermassive black hole mass functions at intermediate redshifts from spheroid and AGN luminosity functionsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006Naoyuki Tamura ABSTRACT Redshift evolution of supermassive black hole mass functions (BHMFs) is investigated up to z, 1. BHMFs at intermediate redshifts are calculated in two ways. One way is from early-type galaxy luminosity functions (LFs); we assume an MBH,Lsph correlation at a redshift by considering a passive evolution of Lsph in the local relationship. The resultant BHMFs (spheroid-BHMFs) from LFs of red-sequence galaxies indicate a slight decrease of number density with increasing redshift at MBH, 107.5,8 M,. Since a redshift evolution in slope and zeropoint of the MBH,Lsph relation is unlikely to be capable of making such an evolution in BHMF, the evolution of the spheroid-BHMFs is perhaps due mainly to the decreasing normalization in the galaxy LFs. We also derive BHMFs from LFs of morphologically selected early-type galaxies. The resultant BHMFs are similar to those from the red-sequence galaxies, but show a small discrepancy at z, 1 corresponding to an increase of supermassive black hole (SMBH) number density by ,0.3 dex. We also investigate how spheroid-BHMFs are affected by uncertainties existing in the derivation in detail. The other way of deriving a BHMF is based on the continuity equation for number density of SMBHs and LFs of active galactic nucleus (AGN). The resultant BHMFs (AGN-BHMFs) show no clear evolution out to z= 1 at MBH, 108 M,, but exhibit a significant decrease with redshift in the lower mass range. Interestingly, these AGN-BHMFs are quite different in the range of MBH, 108 M, from those derived by Merloni (2004), where the fundamental plane of black hole activity is exploited. Comparison of the spheroid-BHMFs with the AGN-BHMFs suggests that at MBH, 108 M,, the spheroid-BHMFs are broadly consistent with the AGN-BHMFs out to z, 1. Although the decrease of SMBH number density with redshift suggested by the spheroid-BHMFs is slightly faster than that suggested by the AGN-BHMFs, we presume this to be due at least partly to a selection effect on the LFs of red-sequence galaxies; the colour selection could miss spheroids with blue colours. The agreement between the spheroid-BHMFs and the AGN-BHMFs appears to support that most of the SMBHs are already hosted by massive spheroids at z, 1 and they evolve without significant mass growth since then. [source] Universal fitting formulae for baryon oscillation surveysMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006Chris Blake ABSTRACT The next generation of galaxy surveys will attempt to measure the baryon oscillations in the clustering power spectrum with high accuracy. These oscillations encode a preferred scale which may be used as a standard ruler to constrain cosmological parameters and dark energy models. In this paper we present simple analytical fitting formulae for the accuracy with which the preferred scale may be determined in the tangential and radial directions by future spectroscopic and photometric galaxy redshift surveys. We express these accuracies as a function of survey parameters such as the central redshift, volume, galaxy number density and (where applicable) photometric redshift error. These fitting formulae should greatly increase the efficiency of optimizing future surveys, which requires analysis of a potentially vast number of survey configurations and cosmological models. The formulae are calibrated using a grid of Monte Carlo simulations, which are analysed by dividing out the overall shape of the power spectrum before fitting a simple decaying sinusoid to the oscillations. The fitting formulae reproduce the simulation results with a fractional scatter of 7 per cent (10 per cent) in the tangential (radial) directions over a wide range of input parameters. We also indicate how sparse-sampling strategies may enhance the effective survey area if the sampling scale is much smaller than the projected baryon oscillation scale. [source] Evolution of 1612-MHz maser emission in expanding circumstellar shellsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2005M. D. Gray ABSTRACT Observations show that 1612-MHz masers of OH/IR stars can fade on a time-scale of a decade. This fading is probably associated with the switch from rapid mass loss, which is ultimately linked with an internal He-shell flash, to the much slower mass loss supported by more quiescent conditions. We study the observed maser decay with a composite computational model, comprising a time-dependent chemical model of the envelope, and a radiation transfer model which provides the maser pumping. Our combined model is able to reproduce the rapid decay of maser intensity, following a sudden drop in the stellar mass-loss rate. The explanation for the rapid fall in maser emission is not a fall in the OH number density, or the kinetic temperature in the inverted layers, but the loss of a radiative pump route which carries population from levels 1 to 4 via levels 16, 15 and 11. The loss of these pump routes is a result, in turn, of a greatly reduced energy density of 53-,m radiation. [source] | ||||||||||||||||||||||