ABSTRACT
Upcoming weak lensing surveys require a detailed theoretical understanding of the matter power spectrum in order to derive accurate and precise cosmological parameter values. While galaxy ...formation is known to play an important role, its precise effects are currently unknown. We present a set of 92 matter power spectra from the OWLS, cosmo-OWLS, and BAryons and HAloes of MAssive Systems simulation suites, including different ΛCDM cosmologies, neutrino masses, subgrid prescriptions, and AGN feedback strengths. We conduct a detailed investigation of the dependence of the relative difference between the total matter power spectra in hydrodynamical and collisionless simulations on the effectiveness of stellar and AGN feedback, cosmology, and redshift. The strength of AGN feedback can greatly affect the power on a range of scales, while a lack of stellar feedback can greatly increase the effectiveness of AGN feedback on large scales. We also examine differences in the initial conditions of hydrodynamic and N-body simulations that can lead to an $\sim 1{{\ \rm per\ cent}}$ discrepancy in the large-scale power, and furthermore show our results to be insensitive to cosmic variance. We present an empirical model capable of predicting the effect of galaxy formation on the matter power spectrum at z = 0 to within $1{{\ \rm per\ cent}}$ for $k\lt 1\, h\, \mathrm{Mpc}^{-1}$, given only the mean baryon fraction in galaxy groups. Differences in group baryon fractions can also explain the quantitative disagreement between predictions from the literature. All total and dark matter only power spectra in this library will be made publicly available at powerlib.strw.leidenuniv.nl.
Despite significant academic and managerial interest in big data, there is a dearth of research on how big data impacts the long‐term firm performance. Reasons for this gap include a lack of ...objective indices to measure big data availability and its impact, and the tendency of studies to ignore the costs associated with collecting and analyzing big data, assuming that big data automatically delivers benefits to firms. Focusing on how firms create and capture value from big data about customers, we use the resource‐based view and three dimensions of big data (i.e., volume, variety, and veracity) to understand when the benefits outweigh the costs. Relying on the number of downloads of mobile device applications, we find that volume of big data has a negative effect on firm performance. This result suggests that the “bigness” of big data alone does not ensure value creation for a firm, and could even constitute a “dark side” of big data. Because big data variety—measured as the number of types of information taken per each application—moderates the negative effects of big data volume, simultaneous high values of volume and variety allow firms to create value that positively affects their performance. In addition, high levels of veracity (i.e., a high percentage of employees devoted to big data analysis), are linked to firms benefiting from big data via value capture. These findings shed light on the circumstances in which big data can be beneficial for firms, contributing to a better theoretical understanding of the opportunities and challenges and providing useful indications to managers.
The evolution of the large-scale distribution of matter is sensitive to a variety of fundamental parameters that characterize the dark matter, dark energy, and other aspects of our cosmological ...framework. Since the majority of the mass density is in the form of dark matter that cannot be directly observed, to do cosmology with large-scale structure, one must use observable (baryonic) quantities that trace the underlying matter distribution in a (hopefully) predictable way. However, recent numerical studies have demonstrated that the mapping between observable and total mass, as well as the total mass itself, are sensitive to unresolved feedback processes associated with galaxy formation, motivating explicit calibration of the feedback efficiencies. Here, we construct a new suite of large-volume cosmological hydrodynamical simulations (called bahamas, for BAryons and HAloes of MAssive Systems), where subgrid models of stellar and active galactic nucleus feedback have been calibrated to reproduce the present-day galaxy stellar mass function and the hot gas mass fractions of groups and clusters in order to ensure the effects of feedback on the overall matter distribution are broadly correct. We show that the calibrated simulations reproduce an unprecedentedly wide range of properties of massive systems, including the various observed mappings between galaxies, hot gas, total mass, and black holes, and represent a significant advance in our ability to mitigate the primary systematic uncertainty in most present large-scale structure tests.
ABSTRACT
Models of cold dark matter (CDM) predict that the distribution of dark matter in galaxy clusters should be cuspy, centrally concentrated. Constant density cores would be strong evidence for ...beyond CDM physics, such as self-interacting dark matter (SIDM). An observable consequence would be oscillations of the brightest cluster galaxy (BCG) in otherwise relaxed galaxy clusters. Offset BCGs have indeed been observed – but only interpreted via a simplified, analytic model of oscillations. We compare these observations to the BAryons and HAloes of MAssive Sysmtes (BAHAMAS)–SIDM suite of cosmological simulations, which include SIDM and a fully hydrodynamical treatment of star formation and feedback. We predict that the median offset of BCGs increases with the SIDM cross-section, cluster mass, and the amount of stellar mass within 10 kpc, while CDM exhibits no trend in mass. Interpolating between the simulated cross-sections, we find that the observations (of 10 clusters) are consistent with CDM at the ∼1.5σ level, and prefer cross-section σ/m < 0.12(0.39) cm2 g−1 at 68 per cent (95 per cent) confidence level. This is on the verge of ruling out velocity-independent dark matter self-interactions as the solution to discrepancies between the predicted and observed behaviour of dwarf galaxies, and will be improved by larger surveys by Euclid or Super-pressure Balloon-borne Imaging Telescope (SuperBIT).
Bone circulation plays an important role in bone physiology, but has been relatively poorly studied, because most techniques of circulatory research are difficult to apply to bone. This article ...summarizes briefly some of the important aspects of the physiology of bone blood flow most relevant to orthopaedics.
The gold standard for experimental measurement of bone blood flow is the radioactive microsphere technique, though advances are being made in other techniques, such as positron emission tomography, laser and ultra-sound Doppler velocimetry, and near infrared spectroscopy, that may provide useful clinical measurement in the future.
Multiple vascular pathways contribute to an adaptive response to traumatic disruption of bone circulation. The microcirculation is not merely a passive conduit for blood flow, but plays an active role in controlling bone processes such as osteochondral ossification.
The pathophysiology of bone circulation has been associated with osteonecrosis, but more and more evidence is pointing to the importance of bone circulation in fracture repair and osteoporosis, both of which are potentially very exciting areas for future studies.
Abstract
Recent studies have presented evidence for tension between the constraints on Ωm and σ8 from the cosmic microwave background (CMB) and measurements of large-scale structure (LSS). This ...tension can potentially be resolved by appealing to extensions of the standard model of cosmology and/or untreated systematic errors in the modelling of LSS, of which baryonic physics has been frequently suggested. We revisit this tension using, for the first time, carefully calibrated cosmological hydrodynamical simulations, which thus capture the backreaction of the baryons on the total matter distribution. We have extended the BAryons and HAloes of MAssive Sysmtes simulations to include a treatment of massive neutrinos, which currently represents the best-motivated extension to the standard model. We make synthetic thermal Sunyaev–Zel'dovich effect, weak galaxy lensing, and CMB lensing maps and compare to observed auto- and cross-power spectra from a wide range of recent observational surveys. We conclude that: (i) in general, there is tension between the primary CMB and LSS when adopting the standard model with minimal neutrino mass; (ii) after calibrating feedback processes to match the gas fractions of clusters, the remaining uncertainties in the baryonic physics modelling are insufficient to reconcile this tension; and (iii) if one accounts for internal tensions in the Planck CMB data set (by allowing the lensing amplitude, ALens, to vary), invoking a non-minimal neutrino mass, typically of 0.2–0.4 eV, can resolve the tension. This solution is fully consistent with separate constraints from the primary CMB and baryon acoustic oscillations.
Research and practice have mostly focused on the “bright side” of social media, aiming to understand and help in leveraging the manifold opportunities afforded by this technology. However, it is ...increasingly observable that social media present enormous risks for individuals, communities, firms, and even for society as a whole. Examples for this “dark side” of social media include cyberbullying, addictive use, trolling, online witch hunts, fake news, and privacy abuse. In this article, we aim to illustrate the multidimensionality of the dark side of social media and describe the related various undesirable outcomes. To do this, we adapt the established social media honeycomb framework to explain the dark side implications of each of the seven functional building blocks: conversations, sharing, presence, relationships, reputation, groups, and identity. On the basis of these reflections, we present a number of avenues for future research, so as to facilitate a better understanding and use of social media.
•The "bright side" of social media and its uptake by society has received much research attention.•The corresponding "dark side" of social media has received much less research attention.•To study the deleterious impacts of social media, we introduce the dark side honeycomb framework.•The framework describes the functional multidimensionality of the dark side of social media.•We use this framework as a basis for a call-to-action for research on the dark side of social media.
ABSTRACT
The recent advent of deep observational surveys of local Milky Way ‘analogues’ and their satellite populations allows us to place the Milky Way in a broader cosmological context and to test ...models of galaxy formation on small scales. In this study, we use the Lambda cold dark matter (ΛCDM)-based ARTEMIS suite of cosmological hydrodynamical simulations containing 45 Milky Way analogue host haloes to make comparisons to the observed satellite luminosity functions, radial distribution functions, and abundance scaling relations from the recent Local Volume and SAGA observational surveys, in addition to the Milky Way and M31. We find that, contrary to some previous claims, ΛCDM-based simulations can successfully and simultaneously capture the mean trends and the diversity in both the observed luminosity and radial distribution functions of Milky Way analogues once important observational selection criteria are factored in. Furthermore, we show that, at fixed halo mass, the concentration of the simulated satellite radial distribution is partly set by that of the underlying smooth dark matter halo, although stochasticity due to the finite number of satellites is the dominant driver of scatter in the radial distribution of satellites at fixed halo mass.
ABSTRACT
Using the artemis set of 45 high-resolution cosmological simulations, we investigate a range of merger-induced dynamical transformations of Milky Way-like galaxies. We first identify ...populations of accreted stars on highly radial orbits, similar to the ‘Gaia Sausage’ in the Milky Way. We show that ≈1/3 of the artemis galaxies contain a similar feature, and confirm that they usually comprise stellar debris from the most massive accreted satellite. Selecting 15 galaxies with discs at the present-day, we study their changes around the times of the GS-like mergers. Dark matter haloes of many of these exhibit global changes in shape and orientation, with almost half becoming significantly more spherical when the mergers occur. Focusing on the galaxies themselves, we find that 4/15 have stellar discs which experience large changes in the orientation of their angular momentum (AM) axes, at rates of up to ∼60 degrees Gyr−1. By calculating the orbital angular momentum axes of the satellites before they are accreted, we show that there is a tendency for the disc’s AM to become more aligned with this axis after the merger. We also investigate the origin of in situ retrograde stars, analogous to the ‘Splash’ in the Milky Way. Tracing them back to earlier snapshots, we demonstrate that they were often disrupted on to their extreme orbits by multiple early mergers. We also find that the total mass of these stars outside the central regions positively correlates with the total accreted stellar mass.
We use the BAHAMAS (BAryons and HAloes of MAssive Systems) and MACSIS (MAssive ClusterS and Intercluster Structures) hydrodynamic simulations to quantify the impact of baryons on the mass ...distribution and dynamics of massive galaxy clusters, as well as the bias in X-ray and weak lensing mass estimates. These simulations use the subgrid physics models calibrated in the BAHAMAS project, which include feedback from both supernovae and active galactic nuclei. They form a cluster population covering almost two orders of magnitude in mass, with more than 3500 clusters with masses greater than 10 super( 14) M... at z = 0. We start by characterizing the clusters in terms of their spin, shape and density profile, before considering the bias in both weak lensing and hydrostatic mass estimates. Whilst including baryonic effects leads to more spherical, centrally concentrated clusters, the median weak lensing mass bias is unaffected by the presence of baryons. In both the dark matter only and hydrodynamic simulations, the weak lensing measurements underestimate cluster masses by ...10 per cent for clusters with M200 = 10 super( 15) M... and this bias tends to zero at higher masses. We also consider the hydrostatic bias when using both the true density and temperature profiles, and those derived from X-ray spectroscopy. When using spectroscopic temperatures and densities, the hydrostatic bias decreases as a function of mass, leading to a bias of ...40 per cent for clusters with M500 greater than or equal to 10 super( 15) M... This is due to the presence of cooler gas in the cluster outskirts. Using mass weighted temperatures and the true density profile reduces this bias to 5-15 per cent. (ProQuest: ... denotes formulae/symbols omitted.)
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