402 research outputs found
Non-universality of the mass function: dependence on the growth rate and power spectrum shape
The abundance of dark matter haloes is one of the key probes of the growth of
structure and expansion history of the Universe. Theoretical predictions for
this quantity usually assume that, when expressed in a certain form, it depends
only on the mass variance of the linear density field. However, cosmological
simulations have revealed that this assumption breaks, leading to 10-20%
systematic effects. In this paper we employ a specially-designed suite of
simulations to further investigate this problem. Specifically, we carry out
cosmological N-body simulations where we systematically vary growth history at
a fixed linear density field, or vary the power spectrum shape at a fixed
growth history. We show that the halo mass function generically depends on
these quantities, thus showing a clear signal of non-universality. Most of this
effect can be traced back to the way in which the same linear fluctuation grows
differently into the nonlinear regime depending on details of its assembly
history. With these results, we propose a parameterization with explicit
dependence on the linear growth rate and power spectrum shape. Using an
independent suite of simulations, we show that this fitting function accurately
captures the mass function of haloes over cosmologies spanning a vast parameter
space, including massive neutrinos and dynamical dark energy. Finally, we
employ this tool to improve the accuracy of so-called cosmology-rescaling
methods and show they can deliver 2% accurate predictions for the halo mass
function over the whole range of currently viable cosmologies
Consistent and simultaneous modelling of galaxy clustering and galaxy-galaxy lensing with Subhalo Abundance Matching
The spatial distribution of galaxies and their gravitational lensing signal
offer complementary tests of galaxy formation physics and cosmology. However,
their synergy can only be fully exploited if both probes are modelled
accurately and consistently. In this paper, we demonstrate that this can be
achieved using an extension of Subhalo Abundance Matching, dubbed SHAMe.
Specifically, we use mock catalogues built from the TNG300 hydrodynamical
simulation to show that SHAMe can simultaneously model the multipoles of the
redshift-space galaxy correlation function and galaxy-galaxy lensing, without
noticeable bias within the statistical sampling uncertainties of a SDSS volume
and on scales r = [0.6-30] Mpc/h. Modelling the baryonic processes in
galaxy-galaxy lensing with a baryonification scheme allows SHAMe's range of
validity to be extended to r = [0.1-30] Mpc/h. Remarkably, our model achieves
this level of precision with just five free parameters beyond those describing
the baryonification model. At fixed cosmology, we find that galaxy-galaxy
lensing provides a general consistency test but little additional information
on galaxy modelling parameters beyond that encoded in the redshift-space
multipoles. It does, however, improve constraints if only the projected
correlation function is available, as in surveys with only photometric
redshifts. We expect SHAMe to have a higher fidelity across a wider range of
scales than more traditional methods such as Halo Occupation Distribution
modelling. Thus it should provide a significantly more powerful and more robust
tool for analysing next-generation large-scale surveys.Comment: 14 pages, 7 figures. Submitted to MNRA
Recognition of Intentional Violations of Active Constraints in Cooperative Manipulation Tasks
Active Constraints (ACs) are high-level control algorithms deployed to assist a human operator in man-machine cooperative tasks [1], and define regions within which it is safe for the robot to move and cut [2]. To enhance the performance in cooperative surgical tasks,
adaptive constraints have been exploited to optimally adjust the provided level of assistance according to some knowledge of the task, hardware or user. In [3] Hidden Markov Models were used for the run-time detection of the user intention to leave a guidance
constraint to circumvent an obstacle. In this work, we present a novel, Neural Network (NN)-based method for the runtime classification of intentional and unintentional violations of ACs, that is trained on either statistical or frequency features from the enforced
constraint forces. We investigate which set of parameters yield faster and more reliable classification results, both for guidance and regional constraints
Nafion-TiO2 composite DMFC membranes: Physico-chemical properties of the filier versus electrochemical performance
TiO2 nanometric powders were prepared via a sol-gel procedure and calcined at various temperatures to obtain different surface and bulk properties. The calcined powders were used as fillers in composite Nafion membranes for application in high temperature direct methanol fuel cells (DMFCs). The powder physico-chemical properties were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and pH measurements. The observed characteristics were correlated to the DMFC electrochemical behaviour. Analysis of the high temperature conductivity and DMFC performance reveals a significant influence of the surface characteristics of the ceramic oxide, such as oxygen functional groups and surface area, on the membrane electrochemical behaviour. A maximum DMFC power density of 350 mW cm-2 was achieved under oxygen feed at 145°C in a pressurized DMFC (2.5 bar, anode and cathode) equipped with TiO2 nano-particles based composite membranes. © 2004 Elsevier Ltd. All rights reserved
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