Large-scale Structural Features Research Articles

DEMNUni: the clustering of large-scale structures in the presence of massive neutrinos

We analyse the clustering features of Large Scale Structures (LSS) in the presence of massive neutrinos, employing a set of large-volume, high-resolution cosmological N-body simulations, where neutrinos are treated as separate collisionless particles. The volume of 8 h-3 Gpc3, combined with a resolution of about 8×1010h-1M⊚ for the cold dark matter (CDM) component, represents a significant improvement over previous N-body simulations in massive neutrino cosmologies. In this work we focus, in the first place, on the analysis of nonlinear effects in CDM and neutrinos perturbations contributing to the total matter power spectrum. We show that most of the nonlinear evolution is generated exclusively by the CDM component. We therefore compare mildly nonlinear predictions from Eulerian Perturbation Theory (PT), and fully nonlinear prescriptions (HALOFIT) with the measurements obtained from the simulations. We find that accounting only for the nonlinear evolution of the CDM power spectrum allows to recover the total matter power spectrum with the same accuracy as the massless case. Indeed, we show that, the most recent version of the (HALOFIT) formula calibrated on ΛCDM simulations can be applied directly to the linear CDM power spectrum without requiring additional fitting parameters in the massive case. As a second step, we study the abundance and clustering properties of CDM halos, confirming that, in massive neutrino cosmologies, the proper definition of the halo bias should be made with respect to the cold rather than the total matter distribution, as recently shown in the literature. Here we extend these results to the redshift space, finding that, when accounting for massive neutrinos, an improper definition of the linear bias can lead to a systematic error of about 1-2 % in the determination of the linear growth rate from anisotropic clustering. This result is quite important if we consider that future spectroscopic galaxy surveys, as e.g. Euclid, are expected to measure the linear growth-rate with statistical errors less than about 3 % at z≲1.

Characteristics of Large-Scale Structures in Supersonic Planar Mixing Layer with Finite Thickness

Nanoparticle-based planar laser scattering (NPLS) experiments and large eddy simulation (LES) were launched to get the fine structure of the supersonic planar mixing layer with finite thickness in the present study. Different from the turbulent development of supersonic planar mixing layer with thin thickness, the development of supersonic planar mixing layer with finite thickness is rapidly. The large-scale structures of mixing layer that possess the characters of quick movement and slow changes transmit to downriver at invariable speed. The transverse results show that the mixing layer is strip of right and dim and possess 3D characteristics. Meanwhile the vortices roll up from two sides to the center. Results indicate that the higher the pressure of the high speed side is, the thicker the mixing layer is. The development of mixing layer is restrained when the pressure of lower speed side is higher. The momentum thickness goes higher with the increase of the clapboard thickness. Through increasing the temperature to change the compression can affect the development of the vortices. The present study can make a contribution to the mixing enhancement and provide initial data for the later investigations.

Supermassive Black Holes, Large Scale Structure and Holography

This analysis considers our universe as a closed Friedmann universe, dominated by vacuum energy in the form of a cosmological constant, with cosmological parameters obtained from full mission Planck satellite observations. A few simple assumptions lead to straightforward calculation of general features of large scale structures in the universe and minimum stellar mass as a function of redshift. Those assumptions also generate upper and lower bounds on supermassive black hole mass in relation to total stellar mass of the host galaxy, consistent with observations across four orders of magnitude of black hole mass and five orders of magnitude of galactic stellar mass. The results are based only on fundamental constants and measured cosmological parameters. No arbitrary parameters are involved.

Advances in modelling groundwater behaviour in Chalk catchments

Abstract Groundwater in Chalk catchments is a major resource that also helps support internationally important habitats and ecosystems. Its dual porosity and dual permeability properties, coupled with large-scale structural features (such as hard rock layers and marls), produce a highly complex hydrogeological system. Recent impacts from groundwater flooding as well as vulnerability to drought have raised questions over the ability of traditional approaches to model these aquifers. Current work on near-surface hydrological processes has highlighted the importance of the soil and weathered zone for controlling recharge rates. In addition, karst-like features, sedimentary deposits and valley bottom processes govern stream–aquifer interaction and present a challenge in their representation in any modelling system. Methods that have, and are being, developed to incorporate these features, and their use in modelling Chalk catchments, are described. These are required in order to address major challenges, such as groundwater flooding and drought impacts, both of which could become more frequent and intense as a result of climate change.

The Application of Increment-Dimensional Blocks PIM on the Base-Isolated Structure

In this paper, seismic elastic and plastic responses of base-isolated structure are investigated, in which the bilinear restore-force model is employed for the isolation equipment. The mutual influences of both damping matrices and stiffness matrices are decoupled by using transition matrix. Based on the increment-dimensional precise integration method (PIM), the increment -dimensional blocks PIM is developed to separate structure characteristics and external forces, which can avoid the calculation of exponential matrices by PIM in each integration step. The results of numerical examples show that the efficiency of the new algorithm is very high in comparing with old method. The advantages of the new algorithm appear more obvious when the characteristics of large-scale structure have slightly changed, and only the external forces vary.

Inhomogeneity and the foundations of concordance cosmology

The apparent accelerating expansion of the universe is forcing us to examine the foundational aspects of the standard model of cosmology—in particular, the fact that dark energy is a direct consequence of the homogeneity assumption. We discuss the foundations of the assumption of spatial homogeneity, in the case when the Copernican principle is adopted. We present results that show how (almost) homogeneity follows from (almost) isotropy of various observables. The analysis requires fully nonlinear field equations—i.e. it is not possible to use second- or higher-order perturbation theory, since one cannot assume a homogeneous and isotropic background. Then we consider what happens if the Copernican principle is abandoned in our Hubble volume. The simplest models are inhomogeneous but spherically symmetric universes which do not require dark energy to fit the distance modulus. Key problems in these models are to compute the CMB anisotropies and the features of large-scale structure. We review how to construct perturbation theory on a non-homogeneous cosmological background, and discuss the complexities that arise in using this to determine the growth of large-scale structure.

GRAPE: GRaphical Abstracted Protein Explorer

The region surrounding a protein, known as the surface of interaction or molecular surface, can provide valuable insight into its function. Unfortunately, due to the complexity of both their geometry and their surface fields, study of these surfaces can be slow and difficult and important features may be hard to identify. Here, we describe our GRaphical ed Protein Explorer, or GRAPE, a web server that allows users to explore abstracted representations of proteins. These abstracted surfaces effectively reduce the level of detail of the surface of a macromolecule, using a specialized algorithm that removes small bumps and pockets, while preserving large-scale structural features. Scalar fields, such as electrostatic potential and hydropathy, are smoothed to further reduce visual complexity. This entirely new way of looking at proteins complements more traditional views of the molecular surface. GRAPE includes a thin 3D viewer that allows users to quickly flip back and forth between both views. ed views provide a fast way to assess both a molecule's shape and its different surface field distributions. GRAPE is freely available at http://grape.uwbacter.org.

Control of a high Reynolds number Mach 0.9 heated jet using plasma actuators

The results of particle image velocimetry (PIV) measurements in a high subsonic, heated, jet forced using localized arc filament plasma actuators (LAFPAs) show that LAFPAs can consistently produce significant mixing enhancement over a wide range of temperatures. These actuators have been used successfully in high Reynolds number, high-speed unheated jets. The facility consists of an axisymmetric jet with different nozzle blocks of exit diameter of 2.54 cm and variable jet temperature in an anechoic chamber. The focus of this paper is on a high subsonic (Mj=0.9) jet. Twelve experiments with various forcing azimuthal modes (m=0, 1, and ±1) and temperatures (To/Ta=1.0, 1.4, and 2.0) at a fixed forcing Strouhal number (StDF=0.3) have been conducted and PIV results compared with the baseline results to characterize the effectiveness of LAFPAs for mixing enhancement. Centerline velocity and turbulent kinetic energy as well as jet width are used for determining the LAFPAs’ effectiveness. The characteristics of large-scale structures are analyzed through the use of Galilean streamlines and swirling strength. Across the range of temperatures collected, the effectiveness of LAFPAs improves as temperature increases. Possible reasons for the increase in effectiveness are discussed.

Systematic coarse graining from structure using internal states: Application to phospholipid/cholesterol bilayer

We present a two-dimensional coarse-grained (CG) model for a lipid membrane composed of phospholipids and cholesterol. The effective CG interactions are determined using radial distribution functions (RDFs) from atom-scale molecular dynamics simulations using the inverse Monte Carlo (IMC) technique, based on our earlier work [T. Murtola et al., J. Chem. Phys. 121, 9156 (2004); J. Chem. Phys. 126, 075101 (2007)]. Here, the original model is improved by including an internal discrete degree of freedom for the phospholipid tails to describe chain ordering. We also discuss the problem of RDF inversion in the presence of internal states, in general, and present a modified IMC method for their inclusion. The new model agrees with the original models on large-scale structural features such as density fluctuations in pure dipalmitoylphosphocholine and cholesterol domain formation at intermediate concentrations and also indicates that ordered and disordered domains form at all cholesterol concentrations, even if the global density remains uniform. The inclusion of ordering also improves transferability of the interactions between different concentrations, but does not eliminate transferability problems completely. We also present a general discussion of problems related to RDF inversion.

Model Update December 2008: Upper Mantle Heterogeneity beneath North America from P-wave Travel Time Tomography with Global and USArray Transportable Array Data

Online material: MIT P -wave tomography model for the United States created using travel-time residuals from the USArray Transportable Array from April 2004 to December 2008. As the Transportable Array of USArray (http://www.iris.edu/USArray/), the seismology component of EarthScope (http://www.earthscope.org/), progresses eastward across the United States, the seismological database available for studies of mantle heterogeneity beneath the North American continent is rapidly expanding. Burdick et al. (2008) published a tomographic model of mantle heterogeneity beneath North America based on USArrayTA P -wave travel time data through November 2007. The purpose of this article is to announce the availability (as an electronic supplement through the SSA Web site. www.seismosoc.org) of model MITP\_USA\_2008DEC, which is based on USArrayTA data through December 2008. By the end of 2008 USArrayTA had begun to illuminate mantle structure below the center of the continent, where systematic high-resolution tomography was previously unavailable. Specifically, data from stations east of the Rocky Mountains provides new constraints on the heterogeneity of the stable North American craton and allows for direct comparison with mantle heterogeneity beneath the tectonically active western margin. Compared to the previous version (Burdick et al. 2008), the current model update refines estimates of mantle heterogeneity around the Yellowstone hotspot, better defining its boundaries and revealing a strong slow anomaly beneath the transition zone. Large-scale structural features in the west, such as the Basin and Range and the Cascadia subduction zone, where data coverage was already good, remain similar to those in the original model, which suggests that the tomographic images of them are now robust. Our tomographic inversions of USArray data are based on the method developed by Karason (2002) and described by Li et al. (2008). We perform global inversions in order to account properly for mantle heterogeneity outside the study area and use an adaptable grid …

Evaporites, petroleum exploration, and the Cenozoic evolution of the Libyan shelf margin, central North Africa

The Mediterranean margin of Libya can be divided into three physiographic provinces, the Pelagian Shelf, the Sirt Embayment, and Offshore Cyrenaica. The petroleum potential of the Pelagian Shelf has been investigated but the Sirt Embayment and Offshore Cyrenaica are almost unexplored. During 2004–2005, new 2D pre-stack time-migrated seismic data were acquired and used to examine the large-scale structural, depositional, and salt tectonic features of the Libyan shelf and slope. The data cover approximately 38,000 line kilometers in water depths ranging from under 50 to over 3000 m. Cenozoic strata along much of the Libyan margin have a demonstrable progradational character punctuated by surfaces of erosion and margin failure. Within the Sirt Embayment the most visible retrogradational surface becomes seismically coincident with the top of Messinian unconformity. This retrogradational surface extends for over 700 km along strike and cuts both sides of the Sirt Embayment. Over 5000 cubic kilometers of material are missing from above this surface. There are two ideas for how retrogradation occurred. One idea relates the retrogradation to margin erosion during the Messinian salinity crisis. The other idea suggests that a large part of the Libyan margin experienced a cataclysmic failure during the late Miocene. Some existing models for offshore Libya have interpreted a widespread layer of halite lying within the Messinian which thickens basinward. This interpretation was probably based on the fact seismic reflection continuity was lost over much of the Sirt Embayment on older data beneath the top Messinian unconformity. The loss of good reflection character adversely affected exploration efforts by obscuring deep structures. Recent seismic data and a current understanding of salt behavior do not support the interpretation of thick halite within the Messinian section. Regional observations do not indicate any mobile halite present in the Sirt Embayment. There is a relatively thin, high amplitude and high velocity layer of non-halite evaporites (mainly anhydrite) which caps the Messinian section. Where this high amplitude and high velocity layer is absent or eroded, seismic continuity within the Messinian interval is restored. Limited available well data support this interpretation. True mobile halite is interpreted to exist in offshore Libya only in the far west of the Pelagian Shelf near the Tunisian border. Beneath the Pelagian Shelf are a series of tight contractional folds that are interpreted to be salt cored. Basins adjacent to the folds display geometries characteristic of salt withdrawal. The fold crests formed bathymetric highs which served as nucleation sites for nummulitic shoal development. These shoals are the principal reservoirs of the Pelagian Shelf.

Nonlinear density fluctuation field theory for large scale structure

We develop an effective field theory of density fluctuations for a Newtonian self-gravitating N-body system in quasi-equilibrium and apply it to a homogeneous universe with small density fluctuations. Keeping the density fluctuations up to second order, we obtain the nonlinear field equation of 2-pt correlation ξ(r), which contains 3-pt correlation and formal ultra-violet divergences. By the Groth–Peebles hierarchical ansatz and mass renormalization, the equation becomes closed with two new terms beyond the Gaussian approximation, and their coefficients are taken as parameters. The analytic solution is obtained in terms of the hypergeometric functions, which is checked numerically. With one single set of two fixed parameters, the correlation ξ(r) and the corresponding power spectrum P(κ) simultaneously match the results from all the major surveys, such as APM, SDSS, 2dfGRS, and REFLEX. The model gives a unifying understanding of several seemingly unrelated features of large scale structure from a field-theoretical perspective. The theory is worth extending to study the evolution effects in an expanding universe.

A comparison of coral reef and coral community fish assemblages in Pacific Panama and environmental factors governing their structure

We compared the reef fish assemblages of two habitats, coral reefs and coral communities (rocky substratum with coral colonies), in the Las Perlas Archipelago in Pacific Panama and attempted to determine associations with habitat variables. We used a modified Atlantic and Gulf Rapid Reef Assessment (AGRRA) survey to record fish species and quadrat transects to determine benthic composition. Multivariate non-parametric multi-dimensional scaling (MDS) ordinations were performed in PRIMER and univariate correlations were used to determine relationships. The reef fish of coral communities were significantly more diverse and species rich than those of coral reefs. The two habitats had significantly different species and size composition, but trophic and family groups overlapped between habitats. Topography, exposure, and the percentage cover of branching and massive corals correlated significantly with differences in fish parameters. The reef fish assemblages of this region appear to be determined more by the larger scale structural features that characterize the two habitats than by features that vary over small scales within the habitats.

Large-Eddy Simulation of High Reynolds Number Cannel Flow applying Explicit Filtering

Correct representation of the effects of the turbulence structure near solid boundaries is very important for successful large-eddy simulation (LES). In the present work, this so-called wall-layer modeling is done on commutation error terms near solid boundaries obtained by explicit filtering. These terms are ignored in conventional LES, but in the present work, these error terms are modeled using a dynamic procedure, making use of the scale-similarity of the modeled terms. It is found, by applying the procedure in LES of a high Reynolds number channel flow, that the dynamic modeling of these error terms makes it possible to gain the roughly same velocity profile as DNS results statistically, and moreover, to simulate the features of large-scale structures instantaneously.

Observational Features of Large-Scale Structures as Revealed by the Catastrophe Model of Solar Eruptions

Large-scale magnetic structures are the main carrier of major eruptions in the solar atmosphere. These structures are rooted in the photosphere and are driven by the unceasing motion of the photospheric material through a series of equilibrium configurations. The motion brings energy into the coronal magnetic field until the system ceases to be in equilibrium. The catastrophe theory for solar eruptions indicates that loss of mechanical equilibrium constitutes the main trigger mechanism of major eruptions, usually shown up as solar flares, eruptive prominences, and coronal mass ejections (CMEs). Magnetic reconnection which takes place at the very beginning of the eruption as a result of plasma instabilities/turbulence inside the current sheet, converts magnetic energy into heating and kinetic energy that are responsible for solar flares, and for accelerating both plasma ejecta (flows and CMEs) and energetic particles. Various manifestations are thus related to one another, and the physics behind these relationships is catastrophe and magnetic reconnection. This work reports on recent progress in both theoretical research and observations on eruptive phenomena showing the above manifestations. We start by displaying the properties of large-scale structures in the corona and the related magnetic fields prior to an eruption, and show various morphological features of the disrupting magnetic fields. Then, in the framework of the catastrophe theory, we look into the physics behind those features investigated in a succession of previous works, and discuss the approaches they used.

Porosity of the upper edifice of Axial Seamount

Seamounts are not solid basalt structures, but have relatively high porosities in their upper crustal sections. At Axial Seamount, off the coast of Oregon, United States, we used on-bottom gravity measurements with a Bell gravity meter within deep-sea submersible Alvin to determine a porosity of 31% for the uppermost ∼100 m of the edifice. The southwestern caldera wall has a porosity of 22% and the caldera floor has a slightly higher porosity of 33%. Seafloor observations and models indicate that these high porosities result from large-scale structural features such as lava tubes and cracks, large lava drain backs, or regions of open pillow basalts in the near subsurface. These high-porosity zones can affect the subsurface permeability, and models of hydrothermal upflow zones explain observed localized gravity anomalies. The variety of hydrothermal alteration, hydrothermally active areas, and open porous features appears to be related to the high porosity that is inferred from geophysical measurements on this active seafloor volcano.

Structural and remote sensing studies of the southern Betsimisaraka Suture, Madagascar

An assessment of the southern Betsimisaraka Suture (B.S.) of southeastern Madagascar using remote sensing and field investigation reveals a complex deformation history. Image processing of Landsat ETM+data and JERS-I Synthetic Aperture Radar (SAR) imagery was integrated with field observations of structural geology and field petrography. The southern B.S. divides the Precambrian basement rocks of Madagascar in two parts. The western part includes Proterozoic rocks whereas the eastern part is an Archean block, named the Masora block. The southern part of the B.S. includes high-grade metamorphic rocks, recording strong deformation and has mineral deposits including chromite, nickel, and emerald, characteristic of oceanic material that is compatible with a suture zone. Large-scale structural features indicate ductile deformation including three generations of folding (F1, F2, and F3) associated with dextral shearing. The first folding event (F1) shows a succession of folds with NE striking axial planes. The second folding event (F2) mainly has north–south striking axial planes and the last event (F3) is represented by mega folds that have ENE–WSW axial plane directions and have NNW and SSE contractional strain patterns. Closure of the Mozambique Ocean between two components of Gondwana sandwiched rocks of the B.S. and formed upright folds and shortening zones which produced N–S trending lineaments. Later dextral movements followed the contraction and formed NW–SE trending lineaments and N–S trending normal faults associated with dextral strike slip faults and fractures.

Nanostructure of the neurocentral growth plate: Insight from scanning small angle X-ray scattering, atomic force microscopy and scanning electron microscopy

In this study, the experimental techniques scanning electron microscopy (SEM) including energy-dispersive X-ray analysis, atomic force microscopy (AFM) and scanning small angle X-ray scattering (SAXS) have been exploited to characterize the organization of large molecules and nanocrystallites in and around the neurocentral growth plate (NGP) of a pig vertebrae L4. The techniques offer unique complementary information on the nano- to micrometer length scale and provide new insight in the changes in the matrix structure during endochondral bone formation. AFM and SEM imaging of the NGP reveal a fibrous network likely to consist of collagen type II and proteoglycans. High-resolution AFM imaging shows that the fibers have a diameter of approximately 100 nm and periodic features along the fibers with a periodicity of 50–70 nm. This is consistent with the SAXS analysis that yields a cross-sectional diameter of the fibers in the range of 90 to 112 nm and a predominant orientation in the longitudinal direction of the NGP. Furthermore, we find inhomogeneities around 7 nm in the NGP by SAXS analysis. Moving towards the bone in the direction perpendicular to the growth plate, a systematic change in apparent thickness is observed, while the large-scale structural features remain constant. In the region of bone, the apparent thickness equals the mean mineral thickness and increases from 2 nm to approximately 3.5 nm as a function distance from the NGP. The mineral particles are organized as plates in a rather compact network structure. We have demonstrated that SEM, AFM and SAXS are valuable tools for the investigation of the organization of large molecules and nanocrystallites in the NGP and adjacent trabecular bone. Our findings will be an important basis for future work into identifying the defects on nanometer length scale responsible for idiopathic scoliosis and other growth-plate-related diseases.

Locating the Past in the Present: Living Traditions and the Performance of Early Music

This study examines the philosophies, values and ethics of Early Music performers who use living musics to inform and enhance their performance styles and techniques. Early Music performers seek to revive lost traditions of performance, relying on spare descriptions and fragmentary evidence. Since the 1950s, several generations of visionary performers have turned to living musical traditions for inspiration and collaboration in the recreation of earlier European repertoires. Early Music specialists who follow this path hold their informants and collaborators in high esteem and treat their beliefs with respect. They often avoid surface aspects of the musics on which they draw, instead favouring large-scale structural features and performance techniques from which they can develop models for their own work. While many have criticized this approach as an appeal to the exotic and as an extension of 19th-century orientalizing projects, few scholarly studies have sought to understand it from the point of view of the musicians themselves. Ethnography in the field of Early Music – in conjunction with the published writings of the musicians – provides a valuable perspective on this living art. Western classical music in general is under-represented in ethnomusicological research and deserves sympathetic, though not necessarily uncritical, ethnographies. Collaborative projects between historical musicologists and ethnomusicologists on the place of past music in the present would benefit both fields.

Structure sensitive photoionization via Rydberg levels

The applicability of Rydberg spectroscopy as a method to fingerprint molecular structures is demonstrated on the example of the azulene/naphthalene system. The fingerprint characteristics of Rydberg spectra are distinctly different from those of other techniques, making the technique useful for the characterization of large-scale structural features. In addition, universal applicability to all neutral or positively charged ions, from small molecules to large composite or polymeric systems, is coupled with straightforward combination with traditional mass spectrometry.