Modeling Of Large-scale Structures Research Articles

Cluster contribution to the X-ray background as a cosmological probe

Extensive measurements of the X-ray background (XRB) yield a reasonably reliable characterisation of its basic properties. Having resolved most of the cosmic XRB into discrete sources, the levels and spectral shapes of its main components can be used to probe both the source populations and also alternative cosmological and large-scale structure models. Recent observations of clusters seem to provide evidence that clusters formed earlier and are more abundant than predicted in the standard $\Lambda$CDM model. This motivates interest in alternative models that predict enhanced power on cluster scales. We calculate predicted levels and spectra of the superposed emission from groups and clusters of galaxies in $\Lambda$CDM and in two viable alternative non-Gaussian ($\chi^2$) and early dark energy models. The predicted levels of the contribution of clusters to the XRB in the non-Gaussian models exceed the measured level at low energies and levels of the residual XRB in the 2-8 keV band; these particular models are essentially ruled out. Our work demonstrates the diagnostic value of the integrated X-ray emission from clusters, by considering also its dependences on different metallicities, gas and temperature profiles, Galactic absorption, merger scenarios, and on a non-thermal pressure component. We also show that the XRB can be used for a upper limit for the concentration parameter value.

An adaptive multi-scale computational modelling of Clare College Bridge

Masonry structures may be modelled as an assembly of linearly elastic bodies (individual bricks or stone-blocks) in unilateral frictional contact. Such models generally constitute a formidable computational challenge owing to the need to resolve interactions between individual bodies, such as detection of crack and openings and the resolution of non-linear equations governing the contact. Even for medium size structures, the large number of blocks from which they are assembled renders a full direct simulation of such structures practically impossible. In this paper, an adaptive multi-scale technique for the modelling of large-scale dynamic structures is implemented and applied to the computer simulation of Clare College Bridge, in Cambridge, UK. The adaptive multi-scale approach enables us to carry out simulations at a complexity normally associated with the cost of modelling the entire structure by a simple continuum model whilst incorporating small scale effects, such as openings of gaps and slippage between individual masonry units, using a systematic and locally optimal criterion.

A Unified Finite-Element Solution From Zero Frequency to Microwave Frequencies for Full-Wave Modeling of Large-Scale Three-Dimensional On-Chip Interconnect Structures

It has been observed that a full-wave finite-element-based solution breaks down at low frequencies. This hinders its application to on-chip problems in which broadband modeling from direct current to microwave frequencies is required. Although a static formulation and a full-wave formulation can be stitched together to solve this problem, it is cumbersome to implement both static and full-wave solvers and make transitions between these two when necessary. In this work, a unified finite-element solution from zero frequency to microwave frequencies is developed for full-wave modeling of large-scale three-dimensional on-chip interconnect structures. In this solution, a single full-wave formulation is used. No switching to a static formulation is needed at low frequencies. This is achieved by first identifying the reason why a full-wave eigenvalue-based solution breaks down at low frequencies, and then developing an approach to eliminate the reason. The low frequency breakdown problem was found to be attributed to the discrepant frequency dependence of the real part and the imaginary part of the eigenvalues, which leads to an ill-conditioned eigenvalue system at low frequencies. The discrepant frequency dependence of the real part and the imaginary part is further attributed to the different scaling of the transverse and longitudinal fields with respect to frequency in a transmission-line type structure. By extracting transverse and longitudinal fields separately in the framework of a full-wave formulation, we avoid the numerical difficulty of solving an ill-conditioned eigen-system at low frequencies. The validity of the proposed approach is demonstrated by numerical and experimental results.

A Fast Frequency-Domain Eigenvalue-Based Approach to Full-Wave Modeling of Large-Scale Three-Dimensional On-Chip Interconnect Structures

As on-chip circuits have scaled into the deep submicron regime, electromagnetics-based analysis has increasingly become essential for high-performance integrated circuit (IC) design. Not only fast, but also high-capacity electromagnetic solutions are demanded to overcome the large problem size facing on-chip design community. In this paper, we present a novel, high-capacity, and fast approach to the full-wave modeling of 3-D on-chip interconnect structures. In this approach, the interconnect structure is decomposed into a number of seeds. In each seed, the original wave propagation problem is represented as a generalized eigenvalue problem. The resulting eigenvalue representation can comprehend both conductor and dielectric losses, arbitrary dielectric and conductor configuration in the transverse cross section, and arbitrary material. A new mode-matching technique applicable to on-chip interconnects is developed to solve large-scale 3-D problems by using 2-D-like CPU time and memory. A junction matrix acceleration technique is proposed to speed up the mode matching process. A fast frequency sweep technique is employed to obtain the response over the entire frequency band by solving at one or a few frequency points only. An extraction technique is developed to obtain S-parameters from the solution of the eigenvalue system. The entire procedure is numerically rigorous without making any theoretical approximation. Experimental and numerical results demonstrate its accuracy and efficiency.

Scaling laws in the cosmic structure and renormalization group

There is an evidence of a scale-invariant matter distribution up to scales over 10 Mpc. We review scaling (fractal or multifractal) models of large-scale structure and their observational evidence. We conclude that the dynamics of cosmological structure formation seems to be driven to a multifractal attractor. This supports previous studies, which we review, of structure formation by means of the renormalization group within a hydrodynamic formulation.

Topological Determinants of Epileptogenesis in Large-Scale Structural and Functional Models of the Dentate Gyrus Derived From Experimental Data

In temporal lobe epilepsy, changes in synaptic and intrinsic properties occur on a background of altered network architecture resulting from cell loss and axonal sprouting. Although modeling studies using idealized networks indicated the general importance of network topology in epilepsy, it is unknown whether structural changes that actually take place during epileptogenesis result in hyperexcitability. To answer this question, we built a 1:1 scale structural model of the rat dentate gyrus from published in vivo and in vitro cell type-specific connectivity data. This virtual dentate gyrus in control condition displayed globally and locally well connected ("small world") architecture. The average number of synapses between any two neurons in this network of over one million cells was less than three, similar to that measured for the orders of magnitude smaller C. elegans nervous system. To study how network architecture changes during epileptogenesis, long-distance projecting hilar cells were gradually removed in the structural model, causing massive reductions in the number of total connections. However, as long as even a few hilar cells survived, global connectivity in the network was effectively maintained and, as a result of the spatially restricted sprouting of granule cell axons, local connectivity increased. Simulations of activity in a functional dentate network model, consisting of over 50,000 multicompartmental single-cell models of major glutamatergic and GABAergic cell types, revealed that the survival of even a small fraction of hilar cells was enough to sustain networkwide hyperexcitability. These data indicate new roles for fractionally surviving long-distance projecting hilar cells observed in specimens from epilepsy patients.

Large-scale simulation of crack propagation based on continuum damage mechanics and two-step mesh partitioning

In this paper, the damage and crack propagation is numerically simulated based on continuum damage mechanics, and the parallel computing technique is utilized for the accurate analysis through the large-scale structural model. Besides the increase of computing burden resulted from the large-scale model, the complexity of the damage model, which involves highly nonlinear effects, increases the quantity of computation. Therefore, the high performance computing power is obtained from the Departmental Computing Grid (DCG) system composed of PC computers in our laboratory. The methodology of DCG is described and a new two-step mesh-partitioning scheme based on the graph-partitioning method is suggested to enhance the load balancing for parallel finite element analysis in the DCG environment. In the two-step mesh-partitioning scheme, the system performance weights are calculated to reflect the effect of heterogeneous system performances and weighted edge and vertex method (WEVM) is adopted to minimize the increase of communications. Based on these circumstances, damage distribution and crack initiation in an edge-cracked plate under Mode-I, -II, -III loading and fuselage structure in tension are analyzed by more than one million degrees of freedom. The possibility of the utilization of Grid computing system can be also addressed from the numerical results.

A galaxy halo model of large-scale structure

We present a new, galaxy halo model of large-scale structure, in which the galaxies entering a given sample are the fundamental objects. Haloes attach to galaxies, in contrast to the standard halo model, in which galaxies attach to haloes. The galaxy halo model pertains mainly to the relationships between the power spectra of galaxies and mass, and their cross-power spectrum. With surprisingly little input, an intuition-aiding approximation to the galaxy-matter cross-correlation coefficient R(k) emerges in terms of the halo mass dispersion. This approximation seems valid to mildly non-linear scales (k ≤ 3 h Mpc -1 ), allowing the measurement of the bias and the matter power spectrum from measurements of the galaxy and galaxy-matter power spectra (or correlation functions). This is especially relevant given the recent advances in precision in measurements of the galaxy-matter correlation function from weak gravitational lensing. The galaxy halo model also addresses the issue of interpreting the galaxy-matter correlation function as an average halo density profile, and provides a simple description of galaxy bias as a function of scale.

Experimental analysis of a semi-actively controlled steel building

The strong need of verifying theories formulated for semi-active control through applications to real structures is due to the fact that theoretical research on semi-active control systems is not matched by a corresponding satisfactory experimental activity. This paper shows how a smart system including magnetorheological devices as damping elements can be implemented in a large-scale structural model, by describing in detail the kind of electronics (dedicated hardware and software) adopted during the experimental campaign. It also describes the most interesting results in terms of reduction of the seismic response (either experimental or numerical) of the semi-actively controlled structure compared to a passive operating control system, and in terms of the evaluation criteria proposed in the benchmark for seismically excited controlled buildings. The paper also explains how to derive from the classical theory of optimal control the adopted control logic, based on a clear physical approach, and provides an exhaustive picture of the time delays characterizing the control sequence.

Nonlinear System Modeling and Velocity Feedback Compensation for Effective Force Testing

Effective force testing (EFT) is a test procedure that can be used to apply real-time earthquake loads to large-scale structural models. The implementation of the EFT method requires velocity feedback compensation for the actuators in order to apply forces accurately to test structures. Nonlinearities in the servosystem have a significant impact on the velocity feedback compensation and test results when large flow demands are present, which can be caused by large structural velocities and/or large forces applied to the test structure. This paper presents a nonlinear servosystem model, upon which a nonlinear compensation scheme is proposed. The model and compensation scheme are experimentally verified. The results indicate that the proposed model accurately describes the servosystem behavior, and with the nonlinear velocity feedback compensation, real-time dynamic testing can be conducted using the EFT method.

Massive Neutrinos and the Halo Model of Large Scale Structure

Measurements of the linear power spectrum of galaxies have placed tight constraints on neutrino masses. We introduce an extended halo model for the effect of neutrinos in the nonlinear regimes probed by weak lensing.

An Experimental Study on the Development of Coherent Structure in a Plane Jet (4th Report, Multi-point Simultaneous Measurement of Two Velocity Components and the Large-scale Structure Model by the KL Expansion)

In order to clarify the large-scale coherent structure in a turbulent plane jet, the simultaneous measurement of the main streamwise and the cross-streamwise velocity at 9 points in the self-preserving region of a turbulent plane jet has been preformed by an array of X-type hot wire probes. From the time variation of the main streamwise fluctuating velocity field, it is found that there exist a pair of fluid lumps with the positive and negative fluctuating velocity on opposite sides of the jet centerline. On the other hand, the instantaneous cross-streamwise fluctuating velocity shows the same sign over the cross-section, i.e., the vertically-striped pattern is formed. As the result of the KL expansion, it is found hat the first u and v modes present a character of the “flapping”, and the second and third modes show the one of the “puffing”. From the combination of the “flapping” and the “puffing”, a new coherent structure model in the self-preserving region of a turbulent plane jet has been developed.

Triaxial haloes, intrinsic alignments and the dark matter power spectrum

We develop the halo model of large-scale structure to include triaxial dark matter haloes and their intrinsic alignments. As a direct application we derive general expressions for the two-point correlation function and the power spectrum. We then focus on the power spectrum and numerically solve the general expressions for two different models of the triaxial profiles. The first is a toy model that allows us to isolate the dependence of clustering on halo shape alone and the second is the more realistic profile model of Jing & Suto. In both cases, we find that the effect of triaxiality is manifest as a suppression of power at the level of ∼5 per cent on scales k∼ 1–10hMpc−1, which in real space corresponds to the virial radii of clusters. When considered by mass, we find that for the first model the effects are again apparent as a suppression of power and that they are more significant for the high-mass haloes. For the Jing & Suto model, we find a suppression of power on large scales followed by a sharp amplification on small scales at the level of ∼10–15 per cent. Interestingly, when averaged over the entire mass function this amplification effect is suppressed. We also find for the one-halo term on scales k < 10hMpc−1 that the power is dominated by ellipsoidal haloes with semi-minor to semi-major axis ratios a/c < 0.7. One of the important features of our formalism is that it allows for the self-consistent inclusion of the intrinsic alignments of haloes. The alignments are specified through the correlation function of halo seeds. We develop a useful toy model for this and then make estimates of the alignment contribution to the power spectrum. Further, through consideration of the (artificial) case where all haloes are perfectly aligned, we calculate the maximum possible contribution to the clustering. We find the hard limit of <10 per cent. Subject to further scrutiny, the proposed toy model may serve as a means for linking the actual observed intrinsic alignments of galaxies to physical quantities of interest.

The Cepheid Distance to NGC 5236 (M83) with the ESO Very Large Telescope

Cepheids have been observed in NGC 5236 (M83) using the Antu (Unit Telescope 1) 8.2 m telescope of the ESO Very Large Telescope with the Focal Reducer/Low Dispersion Spectrograph 1. Repeated imaging observations have been made between 2000 January and 2001 July. Images were obtained in 34 epochs in the V band and in six epochs in the I band. The photometry was made with the ROMAFOT reduction package and checked independently with DoPHOT and a modified version of HSTPHOT. Twelve Cepheid candidates have periods ranging between 12 and 55 days. The dereddened distance modulus is adopted to be (m - M)0 = 28.25 ± 0.15, which corresponds to a distance of 4.5 ± 0.3 Mpc. The Cepheid distance of NGC 5253 has been rediscussed and strengthened by its SN 1972E. The mean distance of (m - M)0 = 28.01 ± 0.15 (based on SN 1972E) shows the galaxy to be a close neighbor of M83, suggesting that the two galaxies may have interacted in the past and thus possibly explaining the amorphous morphology of NGC 5253. The distance difference between M83 and NGC 5253 is only 0.5 ± 0.4 Mpc. The projected distance is only ~ 0.15 Mpc. M83 is the principal member of the nearby M83 group containing also, besides NGC 5253, several dwarf members, for five of which tip of the red giant branch distances are available. The adopted group distance of (m - M)0 = 28.28 ± 0.10 (4.5 ± 0.2 Mpc), together with its mean recession velocity of vLG = 249 ± 42 km s-1, shows again the extreme quietness of the local (1-10 Mpc) expansion field. M83 fits onto the local mean Hubble flow line of the velocity-distance relation (with H0~ 60) with no significant deviation, supporting the earlier conclusion that the local velocity expansion field is remarkably cold on a scale of 10 Mpc, contrary to the predictions of the simplest cold dark matter model for large-scale structure. The role of a cosmological constant has been invoked as a possible solution in providing a nearly uniform force field everywhere in the presence of a lumpy galaxy distribution.

Comment on &amp;quot;The Output Composition Puzzle: A Difference in the Monetary Transmission Mechanism in the Euro Area and U.S.&amp;quot;

Comment on "The Output Composition Puzzle:A Difference in the Monetary Transmission Mechanism in the Euro Area and U.S." by Ignazio Angeloni, Anil K Kashyap, Benoît Mojon, and Daniele Terlizzese Richard H. Clarida (bio) This paper (Angeloni et al., 2003, this issue of JMCB) deploys a range of VAR specifications to look at the monetary transmission mechanism in Europe and U.S. A feature that I like very much is that the specification keeps track of consumption and investment dynamics as well as GDP so that the composition effects of monetary policy can be studied. The paper also checks for robustness by looking at same phenomena in large-scale structural models. The paper finds that much more of the U.S. monetary transmission mechanism operates through consumption, while the European transmission mechanism operates much more through investment. This can be seen from Figures 1 and 2 and Tables 3 and 4. For example, in structural models at an eight-quarter horizon, we see that in the U.S., the consumption impulse is 70% of the size of the GDP impulse, while the investment impulse is only 20%. By contrast, in Europe, the investment impulse is 70% of the magnitude of the GDP impulse. The VAR models tend to show even bigger differences. The paper estimates dynamic structural general equilibrium models to see if they are consistent with VAR evidence. It finds that they can "be tweaked" to fit pattern [End Page 1307] for Europe (by reducing the investment adjust cost parameter below its estimated level). However, the models apparently cannot be tweaked to fit the pattern in the U.S. Richard H. Clarida Richard H. Clarida is a Lowell Harriss Professor of Economics at Columbia University. E-mail: rhc2@columbia.edu Literature Cited Angeloni, Ignazio, Anil K Kashyap, Benoît Mojon, and Daniele Terlizzese (2003). "The output Composition Puzzle: A Difference in the Monetary Transmission Mechanism in the Euro Area and U.S." Journal of Money, Credit, and Banking 35, 1265-1306. (this issue of JMCB) [End Page 1308] Google Scholar Copyright © 2003 The Ohio State University

Substructure and the halo model of large-scale structure

We develop the formalism to include substructure in the halo model of clustering. Real haloes are not likely to be perfectly smooth, but have substructure which has, to date, been neglected in the halo model - our formalism allows one to estimate the effects of this substructure on measures of clustering. We derive expressions for the two-point correlation function, the power-spectrum, the cross-correlation between galaxies and mass, as well as higher order clustering measures. Simple forms of the formulae are obtained for the limit in which the size of the substructure and the mass fraction in it is small. Inclusion of substructure allows for a more accurate analysis of the statistical effects of gravitational lensing. It may also bring the halo model predictions into better agreement with the small-scale structure seen in recent high-resolution simulations of hierarchical clustering.

The use of a laser doppler anemometer to investigate vortex structures in highly turbulent swirl flow when there are predominant fluctuations

The modeling and experimental investigation of large-scale vortex structures at the exit of a model burner of a low-emission combustion chamber when there is artificial generation of air flow-rate fluctuations are considered. A method for the diagnostics of vortex structures is developed using a two-component laser Doppler anemometer, which enables vortex structures in the jet mixing zone to be distinguished. The intensity of the swirling of the flow is calculated. A simplified rapid method of vortex-structure diagnostics is proposed, which significantly reduces the time of the experiment and the number of measurements required.

횡분류(流)(橫噴流)에서 난류 비예흔합 화염의 화염날림에 대한 거대 와(渦)구조 혼합 모텔 적용

횡분류(流)(橫噴流)에서 난류 비예흔합 화염의 화염날림에 대한 거대 와(渦)구조 혼합 모텔 적용

Cluster Evolution in the [ITAL]ROSAT[/ITAL] North Ecliptic Pole Survey

The deepest region of the ROSAT All-Sky Survey, at the north ecliptic pole, has been studied to produce a complete and unbiased X-ray-selected sample of clusters of galaxies. This sample is used to investigate the nature of cluster evolution and to explore the potential implications for large-scale structure models. The survey is 99.6% optically identified. Spectroscopic redshifts have been measured for all the extragalactic identifications. In this Letter, first results on cluster evolution are presented based on a comparison between the number of the observed clusters in the north ecliptic pole survey and the number of expected clusters assuming no-evolution models. At z > 0.3, there is a deficit of clusters with respect to the local universe that is significant at greater than 4.7 σ. The evolution appears to commence at L0.5-2.0 keV > 1.8 × 1044 ergs s-1 in our data. The negative evolution goes in the same direction as the original Extended Medium-Sensitivity Survey result, the results from the 160 deg2 survey, and the recent results from the ROSAT Deep Cluster Survey. At lower redshifts, there is no evidence for evolution, a result in agreement with these and other cluster surveys.

Modelling of large-scale structures arising under developed turbulent convection in a horizontal fluid layer (with application to the problem of tropical cyclone origination)

Abstract. The work is concerned with the results of theoretical and laboratory modelling the processes of the large-scale structure generation under turbulent convection in the rotating-plane horizontal layer of an incompressible fluid with unstable stratification. The theoretical model describes three alternative ways of creating unstable stratification: a layer heating from below, a volumetric heating of a fluid with internal heat sources and combination of both factors. The analysis of the model equations show that under conditions of high intensity of the small-scale convection and low level of heat loss through the horizontal layer boundaries a long wave instability may arise. The condition for the existence of an instability and criterion identifying the threshold of its initiation have been determined. The principle of action of the discovered instability mechanism has been described. Theoretical predictions have been verified by a series of experiments on a laboratory model. The horizontal dimensions of the experimentally-obtained long-lived vortices are 4÷6 times larger than the thickness of the fluid layer. This work presents a description of the laboratory setup and experimental procedure. From the geophysical viewpoint the examined mechanism of the long wave instability is supposed to be adequate to allow a description of the initial step in the evolution of such large-scale vortices as tropical cyclones - a transition form the small-scale cumulus clouds to the state of the atmosphere involving cloud clusters (the stage of initial tropical perturbation).