1,224 research outputs found
S=1/2 Kagome antiferromagnets CsCu_{12}$ with M=Zr and Hf
Magnetization and specific heat measurements have been carried out on
CsCuZrF and CsCuHfF single crystals, in which
Cu ions with spin-1/2 form a regular Kagom\'{e} lattice. The
antiferromagnetic exchange interaction between neighboring Cu spins is
K and 540 K for CsCuZrF and
CsCuHfF, respectively. Structural phase transitions were
observed at K and 175 K for CsCuZrF and
CsCuHfF, respectively. The specific heat shows a small bend
anomaly indicative of magnetic ordering at K and 24.5 K in
CsCuZrF and CsCuHfF, respectively. Weak
ferromagnetic behavior was observed below . This weak
ferromagnetism should be ascribed to the antisymmetric interaction of the
Dzyaloshinsky-Moriya type that are generally allowed in the Kagom\'{e} lattice.Comment: 6 pages, 4 figure. Conference proceeding of Highly Frustrated
Magnetism 200
Redshift-space Distortions of the Power Spectrum of Cosmological Objects on a Light Cone : Explicit Formulations and Theoretical Implications
We examine the effects of the linear and the cosmological redshift-space
distortions on the power spectrum of cosmological objects on a light cone. We
develop theoretical formulae for the power spectrum in linear theory of density
perturbations in a rigorous manner starting from first principle corresponding
to Fourier analysis. Approximate formulae, which are useful properly to
incorporate the redshift-space distortion effects into the power spectrum are
derived, and the validity is examined. Applying our formulae to galaxy and
quasar samples which roughly match the SDSS survey, we will show how the
redshift-space distortions distort the power spectrum on the light cone
quantitatively.Comment: 30 pages, Accepted for publication in the Astrophysical Journal
Supplement Serie
Clustering of dark matter halos on the light-cone: scale-, time- and mass-dependence of the halo biasing in the Hubble volume simulations
We develop a phenomenological model to predict the clustering of dark matter
halos on the light-cone by combining several existing theoretical models.
Assuming that the velocity field of halos on large scales is approximated by
linear theory, we propose an empirical prescription of a scale-, mass-, and
time-dependence of halo biasing. We test our model against the Hubble Volume
-body simulation and examine its validity and limitations. We find a good
agreement in two-point correlation functions of dark matter halos between the
phenomenological model predictions and measurements from the simulation for
Mpc both in the real and redshift spaces. Although calibrated on the
mass scale of groups and clusters and for redshifts up to , the model
is quite general and can be applied to a wider range of astrophysical objects,
such as galaxies and quasars, if the relation between dark halos and visible
objects is specified.Comment: 5 pages, 2 figures, ApJL accepted. New references adde
Confronting cold dark matter cosmologies with strong clustering of Lyman break galaxies at
We perform a detailed analysis of the statistical significance of a
concentration of Lyman break galaxies at recently discovered by
Steidel et al. (1997), using a series of N-body simulations with
particles in a (100\himpc)^3 comoving box. While the observed number density
of Lyman break galaxies at implies that they correspond to systems
with dark matter halos of \simlt 10^{12}M_\odot, the resulting clustering of
such objects on average is not strong enough to be reconciled with the
concentration if it is fairly common; we predict one similar concentration
approximately per () fields in three representative cold dark matter
models. Considering the current observational uncertainty of the frequency of
such clustering at , it would be premature to rule out the models, but
the future spectroscopic surveys in a dozen fields could definitely challenge
all the existing cosmological models a posteriori fitted to the universe.Comment: the final version which matchs that published in ApJ Letters (Feb
1998); compared with the previous versions, the predictions for the SCDM
model are slightly changed; Latex, 11 pages, including 3 ps figure
Can Geometric Test Probe the Cosmic Equation of State ?
Feasibility of the geometric test as a probe of the cosmic equation of state
of the dark energy is discussed assuming the future 2dF QSO sample. We examine
sensitivity of the QSO two-point correlation functions, which are theoretically
computed incorporating the light-cone effect and the redshift distortions, as
well as the nonlinear effect, to a bias model whose evolution is
phenomenologically parameterized. It is shown that the correlation functions
are sensitive on a mean amplitude of the bias and not to the speed of the
redshift evolution. We will also demonstrate that an optimistic geometric test
could suffer from confusion that a signal from the cosmological model can be
confused with that from a stochastic character of the bias.Comment: 11 pages, including 3 figures, accepted for publication in ApJ
A Parallel and Distributed Analysis Pipeline for Performance Tree Evaluation
Performance Trees are a unifying framework for the specification of performance queries involving measures and requirements. This paper describes an evaluation environment for Performance Trees comprising a client-side Performance Query Editor, incorporated as a module of the PIPE2 Petri net tool, and a cluster-based server-side evaluation engine. The latter combines the capabilities of a number of parallel and distributed analysis tools
Nonlinear Stochastic Biasing of Peaks and Halos: Scale-Dependence, Time-Evolution, and Redshift-Space Distortion from Cosmological N-body Simulations
We quantify the degree of nonlinearity and stochasticity of the clustering of
biased objects, using cosmological N-body simulations. Adopting the peaks and
the halos as representative biasing models, we focus on the two-point
correlation of the biased objects, dark matter and their cross-correlation.
Especially, we take account of the effect of redshift-space distortion and
attempt to clarify the scale-dependence and the time-dependence by analyzing
the biasing factor and the cross-correlation factor. On small scales,
stochasticity and nonlinearity become appreciable and strongly
object-dependent, especially in redshift space due to the pair-wise velocity
dispersion of the biased objects. Nevertheless, an approximation of
deterministic linear biasing works reasonably well even in the quasi-linear regime
Mpc, and linear redshift-space distortion explains the clustering amplitudes in
redshift space in this regime.Comment: 17 pages, 9 figures, accepted for publication in PAS
Nonlinear Stochastic Biasing of Galaxies and Dark Halos in Cosmological Hydrodynamic Simulations
We perform an extensive analysis of nonlinear and stochastic biasing of
galaxies and dark halos in spatially flat low-density CDM universe using
cosmological hydrodynamic simulations. We compare their biasing properties with
the predictions of an analytic halo biasing model. Dark halos in our
simulations exhibit reasonable agreement with the predictions only on scales
larger than 10h^{-1}Mpc, and on smaller scales the volume exclusion effect of
halos due to their finite size becomes substantial. Interestingly the biasing
properties of galaxies are better described by extrapolating the halo biasing
model predictions.
We also find the clear dependence of galaxy biasing on their formation epoch;
the distribution of old populations of galaxies tightly correlates with the
underlying mass density field, while that of young populations is slightly more
stochastic and anti-biased relative to dark matter. The amplitude of two-point
correlation function of old populations is about 3 times larger than that of
the young populations. Furthermore, the old population of galaxies reside
within massive dark halos while the young galaxies are preferentially formed in
smaller dark halos. Assuming that the observed early and late-type galaxies
correspond to the simulated old and young populations of galaxies,
respectively, all of these segregations of galaxies are consistent with
observational ones for the early and late-type of galaxies such as the
morphology--density relation of galaxies.Comment: 28 pages, 14 figures, accepted for publication in ApJ, Abstract
abridged. For preprint with higher-resolution PS files, see
ftp://www.kusastro.kyoto-u.ac.jp/pub/kohji/ytjs2001
Performance Trees: Implementation And Distributed Evaluation
In this paper, we describe the first realisation of an evaluation environment for Performance Trees, a recently proposed formalism for the specification of performance properties and measures. In particular, we present details of the architecture and implementation of this environment that comprises a client-side model and performance query specification tool, and a server-side distributed evaluation engine, supported by a dedicated computing cluster. The evaluation engine combines the analytic capabilities of a number of distributed tools for steady-state, passage time and transient analysis, and also incorporates a caching mechanism to avoid redundant calculations. We demonstrate in the context of a case study how this analysis pipeline allows remote users to design their models and performance queries in a sophisticated yet easy to use framework, and subsequently evaluate them by harnessing the computing power of a Grid cluster back-end.Accepted versio
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