349 research outputs found
Design and Implementation of CAOS: An Implicitly Parallel Language for the High-Performance Simulation of Cellular Automata
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First laboratory results from FOURIER, the initial science combiner at the MROI
Non-linear CMB lensing with neutrinos and baryons: FLAMINGO simulations versus fast approximations
Weak lensing of the cosmic microwave background is rapidly emerging as a powerful probe of neutrinos, dark energy, and newphysics. We present a fast computation of the non-linear CMB lensing power spectrum that combines non-linear perturbationtheory at early times with powerspectrum emulation using cosmologicalsimulations at late times.Comparing our calculation withlight-cones from the FLAMINGO 5.6 Gpc cube dark-matter-only simulation, we confirm its accuracy to 1 per cent (2 per cent)up to multipoles L = 3000 (L = 5000) for a ΜCDM cosmology consistent with current data. Clustering suppression due tosmall-scale baryonic phenomena such as feedback from active galactic nuclei can reduce the lensing power by ⌠10 per cent.To our perturbation theory and emulator-based calculation, we add SP(k), a new fitting function for this suppression, andconfirm its accuracy compared to the FLAMINGO hydrodynamic simulations to 4 per cent at L = 5000, with similar accuracy formassive neutrino models. We further demonstrate that scale-dependent suppression due to neutrinos and baryons approximatelyfactorize, implying that a careful treatment of baryonic feedback can limit biasing neutrino mass constraints
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The Magdalena Ridge Observatory Interferometer: 2014 status update
The Magdalena Ridge Observatory Interferometer has been designed to be a 10 à 1.4 m aperture long-baseline optical/near-infrared interferometer in an equilateral "Y" configuration, and is being deployed west of Socorro, NM on the Magdalena Ridge. Unfortunately, first light for the facility has been delayed due to the current difficult funding regime, but during the past two years we have made substantial progress on many of the key subsystems for the array. The design of all these subsystems is largely complete, and laboratory assembly and testing, and the installation and site acceptance testing of key components on the Ridge are now underway. This paper serves as an overview and update on the facility's present status and changes since 2012, and the plans for future activities and eventual operations of the facilities. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.The Magdalena Ridge Observatory Interferometer is funded by the U.S. Department of Transportation, the State of New
Mexico, and New Mexico Tech with previous funding from the Navy Research Laboratory (NRL, agreement no.
N00173-01-2-C902).This is the final published version of the article, also available from SPIE at http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1891908. Copyright 2014 Society of Photo Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. http://dx.doi.org/10.1117/12.205733
The FLAMINGO project: revisiting the tension and the role of baryonic physics
A number of recent studies have found evidence for a tension between
observations of large-scale structure (LSS) and the predictions of the standard
model of cosmology with the cosmological parameters fit to the cosmic microwave
background (CMB). The origin of this ' tension' remains unclear, but
possibilities include new physics beyond the standard model, unaccounted for
systematic errors in the observational measurements and/or uncertainties in the
role that baryons play. Here we carefully examine the latter possibility using
the new FLAMINGO suite of large-volume cosmological hydrodynamical simulations.
We project the simulations onto observable harmonic space and compare with
observational measurements of the power and cross-power spectra of cosmic
shear, CMB lensing, and the thermal Sunyaev-Zel'dovich (tSZ) effect. We explore
the dependence of the predictions on box size and resolution, cosmological
parameters including the neutrino mass, and the efficiency and nature of
baryonic 'feedback'. Despite the wide range of astrophysical behaviours
simulated, we find that baryonic effects are not sufficiently large to remove
the tension. Consistent with recent studies, we find the CMB lensing
power spectrum is in excellent agreement with the standard model, whilst the
cosmic shear power spectrum, tSZ effect power spectrum, and the cross-spectra
between shear, CMB lensing, and the tSZ effect are all in varying degrees of
tension with the CMB-specified standard model. These results suggest that some
mechanism is required to slow the growth of fluctuations at late times and/or
on non-linear scales, but that it is unlikely that baryon physics is driving
this modification.Comment: 26 pages, 12 figures, MNRAS, accepted with minor revision
Pion and proton showers in the CALICE scintillator-steel analogue hadron calorimeter
Showers produced by positive hadrons in the highly granular CALICE
scintillator-steel analogue hadron calorimeter were studied. The experimental
data were collected at CERN and FNAL for single particles with initial momenta
from 10 to 80 GeV/c. The calorimeter response and resolution and spatial
characteristics of shower development for proton- and pion-induced showers for
test beam data and simulations using Geant4 version 9.6 are compared.Comment: 26 pages, 16 figures, JINST style, changes in the author list, typos
corrected, new section added, figures regrouped. Accepted for publication in
JINS
Emission and chemistry of organic carbon in the gas and aerosol phase at a sub-urban site near Mexico City in March 2006 during the MILAGRO study
Volatile organic compounds (VOCs) and carbonaceous aerosol were measured at a sub-urban site near Mexico City in March of 2006 during the MILAGRO study (Megacity Initiative: Local and Global Research Objectives). Diurnal variations of hydrocarbons, elemental carbon (EC) and hydrocarbon-like organic aerosol (HOA) were dominated by a high peak in the early morning when local emissions accumulated in a shallow boundary layer, and a minimum in the afternoon when the emissions were diluted in a significantly expanded boundary layer and, in case of the reactive gases, removed by OH. In comparison, diurnal variations of species with secondary sources such as the aldehydes, ketones, oxygenated organic aerosol (OOA) and water-soluble organic carbon (WSOC) stayed relatively high in the afternoon indicating strong photochemical formation. Emission ratios of many hydrocarbon species relative to CO were higher in Mexico City than in the U.S., but we found similar emission ratios for most oxygenated VOCs and organic aerosol. Secondary formation of acetone may be more efficient in Mexico City than in the U.S., due to higher emissions of alkane precursors from the use of liquefied petroleum gas. Secondary formation of organic aerosol was similar between Mexico City and the U.S. Combining the data for all measured gas and aerosol species, we describe the budget of total observed organic carbon (TOOC), and find that the enhancement ratio of TOOC relative to CO is conserved between the early morning and mid afternoon despite large compositional changes. Finally, the influence of biomass burning is investigated using the measurements of acetonitrile, which was found to correlate with levoglucosan in the particle phase. Diurnal variations of acetonitrile indicate a contribution from local burning sources. Scatter plots of acetonitrile versus CO suggest that the contribution of biomass burning to the enhancement of most gas and aerosol species was not dominant and perhaps not dissimilar from observations in the U.S
The FLAMINGO project: cosmological hydrodynamical simulations for large-scale structure and galaxy cluster surveys
We introduce the Virgo Consortium's FLAMINGO suite of hydrodynamical
simulations for cosmology and galaxy cluster physics. To ensure the simulations
are sufficiently realistic for studies of large-scale structure, the subgrid
prescriptions for stellar and AGN feedback are calibrated to the observed
low-redshift galaxy stellar mass function and cluster gas fractions. The
calibration is performed using machine learning, separately for three
resolutions. This approach enables specification of the model by the
observables to which they are calibrated. The calibration accounts for a number
of potential observational biases and for random errors in the observed stellar
masses. The two most demanding simulations have box sizes of 1.0 and 2.8 Gpc
and baryonic particle masses of and ,
respectively. For the latter resolution the suite includes 12 model variations
in a 1 Gpc box. There are 8 variations at fixed cosmology, including shifts in
the stellar mass function and/or the cluster gas fractions to which we
calibrate, and two alternative implementations of AGN feedback (thermal or
jets). The remaining 4 variations use the unmodified calibration data but
different cosmologies, including different neutrino masses. The 2.8 Gpc
simulation follows particles, making it the largest ever
hydrodynamical simulation run to . Lightcone output is produced on-the-fly
for up to 8 different observers. We investigate numerical convergence, show
that the simulations reproduce the calibration data, and compare with a number
of galaxy, cluster, and large-scale structure observations, finding very good
agreement with the data for converged predictions. Finally, by comparing
hydrodynamical and `dark-matter-only' simulations, we confirm that baryonic
effects can suppress the halo mass function and the matter power spectrum by up
to per cent.Comment: 44 pages, 23 figures. Accepted for publication in MNRAS. V3 includes
changes made in published version: jet simulations were redone to fix a bug,
but the differences are nearly invisible. For visualizations, see the
FLAMINGO website at https://flamingo.strw.leidenuniv.nl
FLAMINGO: Calibrating large cosmological hydrodynamical simulations with machine learning
To fully take advantage of the data provided by large-scale structure
surveys, we need to quantify the potential impact of baryonic effects, such as
feedback from active galactic nuclei (AGN) and star formation, on cosmological
observables. In simulations, feedback processes originate on scales that remain
unresolved. Therefore, they need to be sourced via subgrid models that contain
free parameters. We use machine learning to calibrate the AGN and stellar
feedback models for the FLAMINGO cosmological hydrodynamical simulations. Using
Gaussian process emulators trained on Latin hypercubes of 32 smaller-volume
simulations, we model how the galaxy stellar mass function and cluster gas
fractions change as a function of the subgrid parameters. The emulators are
then fit to observational data, allowing for the inclusion of potential
observational biases. We apply our method to the three different FLAMINGO
resolutions, spanning a factor of 64 in particle mass, recovering the observed
relations within the respective resolved mass ranges. We also use the
emulators, which link changes in subgrid parameters to changes in observables,
to find models that skirt or exceed the observationally allowed range for
cluster gas fractions and the stellar mass function. Our method enables us to
define model variations in terms of the data that they are calibrated to rather
than the values of specific subgrid parameters. This approach is useful,
because subgrid parameters are typically not directly linked to particular
observables, and predictions for a specific observable are influenced by
multiple subgrid parameters.Comment: 24 pages, 10 figures (Including the appendix). Submitted to MNRAS.
For visualisations, see the FLAMINGO website at
https://flamingo.strw.leidenuniv.nl
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