1,406 research outputs found
Halo bias in the excursion set approach with correlated steps
In the Excursion Set approach, halo abundances and clustering are closely
related. This relation is exploited in many modern methods which seek to
constrain cosmological parameters on the basis of the observed spatial
distribution of clusters. However, to obtain analytic expressions for these
quantities, most Excursion Set based predictions ignore the fact that, although
different k-modes in the initial Gaussian field are uncorrelated, this is not
true in real space: the values of the density field at a given spatial
position, when smoothed on different real-space scales, are correlated in a
nontrivial way. We show that when the excursion set approach is extended to
include such correlations, then one must be careful to account for the fact
that the associated prediction for halo bias is explicitly a real-space
quantity. Therefore, care must be taken when comparing the predictions of this
approach with measurements in simulations, which are typically made in
Fourier-space. We show how to correct for this effect, and demonstrate that
ignorance of this effect in recent analyses of halo bias has led to incorrect
conclusions and biased constraints.Comment: 7 pages, 3 figures; v2 -- minor clarifications, accepted in MNRA
Are you approaching me? Motor execution influences perceived action orientation
Human observers are especially sensitive to the actions of conspecifics that match their own actions. This has been proposed to be critical for social interaction, providing the basis for empathy and joint action. However, the precise relation between observed and executed actions is still poorly understood. Do ongoing actions change the way observers perceive others' actions? To pursue this question, we exploited the bistability of depth-ambiguous point-light walkers, which can be perceived as facing towards the viewer or as facing away from the viewer. We demonstrate that point-light walkers are perceived more often as facing the viewer when the observer is walking on a treadmill compared to when the observer is performing an action that does not match the observed behavior (e.g., cycling). These findings suggest that motor processes influence the perceived orientation of observed actions: Acting observers tend to perceive similar actions by conspecifics as oriented towards themselves. We discuss these results in light of the possible mechanisms subtending action-induced modulation of perception
Peaks theory and the excursion set approach
We describe a model of dark matter halo abundances and clustering which
combines the two most widely used approaches to this problem: that based on
peaks and the other based on excursion sets. Our approach can be thought of as
addressing the cloud-in-cloud problem for peaks and/or modifying the excursion
set approach so that it averages over a special subset, rather than all
possible walks. In this respect, it seeks to account for correlations between
steps in the walk as well as correlations between walks. We first show how the
excursion set and peaks models can be written in the same formalism, and then
use this correspondence to write our combined excursion set peaks model. We
then give simple expressions for the mass function and bias, showing that even
the linear halo bias factor is predicted to be k-dependent as a consequence of
the nonlocality associated with the peak constraint. At large masses, our model
has little or no need to rescale the variable delta_c from the value associated
with spherical collapse, and suggests a simple explanation for why the linear
halo bias factor appears to lie above that based on the peak-background split
at high masses when such a rescaling is assumed. Although we have concentrated
on peaks, our analysis is more generally applicable to other traditionally
single-scale analyses of large-scale structure.Comment: 10 pages, 4 figures; v2 -- minor changes, added discussion in sec2.2,
fixed a typo. Accepted in MNRA
Optimal linear reconstruction of dark matter from halo catalogs
We derive the weight function w(M) to apply to dark-matter halos that
minimizes the stochasticity between the weighted halo distribution and its
underlying mass density field. The optimal w(M) depends on the range of masses
being used in the estimator. In N-body simulations, the Poisson estimator is up
to 15 times noisier than the optimal. Implementation of the optimal weight
yields significantly lower stochasticity than weighting halos by their mass,
bias or equal. Optimal weighting could make cosmological tests based on the
matter power spectrum or cross-correlations much more powerful and/or
cost-effective. A volume-limited measurement of the mass power spectrum at
k=0.2h/Mpc over the entire z<1 universe could ideally be done using only 6
million redshifts of halos with mass M>6\times10^{13}h^{-1}M_\odot
(1\times10^{13}) at z=0 (z=1); this is 5 times fewer than the Poisson model
predicts. Using halo occupancy distributions (HOD) we find that
uniformly-weighted catalogs of luminous red galaxies require >3 times more
redshifts than an optimally-weighted halo catalog to reconstruct the mass to
the same accuracy. While the mean HODs of galaxies above a threshold luminosity
are similar to the optimal w(M), the stochasticity of the halo occupation
degrades the mass estimator. Blue or emission-line galaxies are about 100 times
less efficient at reconstructing mass than an optimal weighting scheme. This
suggests an efficient observational approach of identifying and weighting halos
with a deep photo-z survey before conducting a spectroscopic survey. The
optimal w(M) and mass-estimator stochasticity predicted by the standard halo
model for M>10^{12}h^{-1}M_\odot are in reasonable agreement with our
measurements, with the important exceptions that the halos must be assumed to
be linearly biased samples of a "halo field" that is distinct from the mass
field. (Abridged)Comment: Added Figure 3 to show the scatter between the weighted halo field vs
the mass field, Accepted for publication in MNRA
Large scale bias and the inaccuracy of the peak-background split
The peak-background split argument is commonly used to relate the abundance
of dark matter halos to their spatial clustering. Testing this argument
requires an accurate determination of the halo mass function. We present a
Maximum Likelihood method for fitting parametric functional forms to halo
abundances which differs from previous work because it does not require binned
counts. Our conclusions do not depend on whether we use our method or more
conventional ones. In addition, halo abundances depend on how halos are
defined. Our conclusions do not depend on the choice of link length associated
with the friends-of-friends halo-finder, nor do they change if we identify
halos using a spherical overdensity algorithm instead. The large scale halo
bias measured from the matter-halo cross spectrum b_x and the halo
autocorrelation function b_xi (on scales k~0.03h/Mpc and r ~50 Mpc/h) can
differ by as much as 5% for halos that are significantly more massive than the
characteristic mass M*. At these large masses, the peak background split
estimate of the linear bias factor b1 is 3-5% smaller than b_xi, which is 5%
smaller than b_x. We discuss the origin of these discrepancies: deterministic
nonlinear local bias, with parameters determined by the peak-background split
argument, is unable to account for the discrepancies we see. A simple linear
but nonlocal bias model, motivated by peaks theory, may also be difficult to
reconcile with our measurements. More work on such nonlocal bias models may be
needed to understand the nature of halo bias at this level of precision.Comment: MNRAS accepted. New section with Spherical Overdensity identified
halos included. Appendix enlarge
The nonlinear redshift space probability distribution function in models with local primordial non-Gaussianity
We use the ellipsoidal collapse approximation to investigate the nonlinear
redshift space evolution of the density field with primordial non-Gaussianity
of the local f_{nl}-type. We utilize the joint distribution of eigenvalues of
the initial non-Gaussian shear field and evaluate the evolved redshift space
probability distribution function (PDF). It is shown that, similar to the real
space analysis, the underdense tail of the nonlinear redshift space PDF differs
significantly from that for Gaussian initial conditions. We also derive the
lowest order correction of the Kaiser's formulain the presence of a non-zero
f_{nl}.Comment: Matched version accepted by MNRA
The clustering of Galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey : including covariance matrix errors
JP acknowledges support from the UK Science & Technology Facilities Council (STFC) through the consolidated grant ST/K0090X/1 and from the European Research Council through the ‘Starting Independent Research’ grant 202686, MDEPUGS. AGS acknowledges support from the Trans-regional Collaborative Research Centre TR33 ‘The Dark Universe’ of the German Research Foundation (DFG).We present improved methodology for including covariance matrices in the error budget of Baryon Oscillation Spectroscopic Survey (BOSS) galaxy clustering measurements, revisiting Data Release 9 (DR9) analyses, and describing a method that is used in DR10/11 analyses presented in companion papers. The precise analysis method adopted is becoming increasingly important, due to the precision that BOSS can now reach: even using as many as 600 mock catalogues to estimate covariance of two-point clustering measurements can still lead to an increase in the errors of ∼20 per cent, depending on how the cosmological parameters of interest are measured. In this paper, we extend previous work on this contribution to the error budget, deriving formulae for errors measured by integrating over the likelihood, and to the distribution of recovered best-fitting parameters fitting the simulations also used to estimate the covariance matrix. Both are situations that previous analyses of BOSS have considered. We apply the formulae derived to baryon acoustic oscillation (BAO) and redshift-space distortion (RSD) measurements from BOSS in our companion papers. To further aid these analyses, we consider the optimum number of bins to use for two-point measurements using the monopole power spectrum or correlation function for BAO, and the monopole and quadrupole moments of the correlation function for anisotropic-BAO and RSD measurements.Publisher PDFPeer reviewe
Alzheimer's early detection in post-acute COVID-19 syndrome: a systematic review and expert consensus on preclinical assessments.
The risk of developing Alzheimer's disease (AD) in older adults increasingly is being discussed in the literature on Post-Acute COVID-19 Syndrome (PACS). Remote digital Assessments for Preclinical AD (RAPAs) are becoming more important in screening for early AD, and should always be available for PACS patients, especially for patients at risk of AD. This systematic review examines the potential for using RAPA to identify impairments in PACS patients, scrutinizes the supporting evidence, and describes the recommendations of experts regarding their use.
We conducted a thorough search using the PubMed and Embase databases. Systematic reviews (with or without meta-analysis), narrative reviews, and observational studies that assessed patients with PACS on specific RAPAs were included. The RAPAs that were identified looked for impairments in olfactory, eye-tracking, graphical, speech and language, central auditory, or spatial navigation abilities. The recommendations' final grades were determined by evaluating the strength of the evidence and by having a consensus discussion about the results of the Delphi rounds among an international Delphi consensus panel called IMPACT, sponsored by the French National Research Agency. The consensus panel included 11 international experts from France, Switzerland, and Canada.
Based on the available evidence, olfaction is the most long-lasting impairment found in PACS patients. However, while olfaction is the most prevalent impairment, expert consensus statements recommend that AD olfactory screening should not be used on patients with a history of PACS at this point in time. Experts recommend that olfactory screenings can only be recommended once those under study have reported full recovery. This is particularly important for the deployment of the olfactory identification subdimension. The expert assessment that more long-term studies are needed after a period of full recovery, suggests that this consensus statement requires an update in a few years.
Based on available evidence, olfaction could be long-lasting in PACS patients. However, according to expert consensus statements, AD olfactory screening is not recommended for patients with a history of PACS until complete recovery has been confirmed in the literature, particularly for the identification sub-dimension. This consensus statement may require an update in a few years
Symbols of Power: The Firearm Paintings of Madjedbebe (Malakunanja II)
Depictions of firearms in Australian Aboriginal rock art provide a unique opportunity to archaeologically explore the roles that this type of material culture played in times of culture contact. From the earliest interactions with explorers to the buffalo shooting enterprises of the twentieth century—firearms played complex and shifting roles in western Arnhem Land Aboriginal societies. The site of Madjedbebe (sometimes referred to as Malakunanja II in earlier academic literature) in Jabiluka (Mirarr Country), offers the opportunity to explore these shifting roles over time with an unprecedented 16 paintings of firearms spanning the nineteenth and twentieth centuries. This rock art provides evidence for early firearms as objects of curiosity and threat to local groups, as well as evidence for later personal ownership and use of such weaponry. Moreover, we argue that the rock art suggests increasing incorporation of firearms into traditional cultural belief and artistic systems over time with Madjedbebe playing a key role in the communication of the cultural meanings behind this new subject matter
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