80 research outputs found
Modification of the halo mass function by kurtosis associated with primordial non-Gaussianity
We study the halo mass function in the presence of the kurtosis type of
primordial non-Gaussianity. The kurtosis corresponds to the trispectrum as
defined in Fourier space. The primordial trispectrum is commonly characterized
by two parameters, and . As applications of the
derived non-Gaussian mass function, we consider the effect on the abundance of
void structure, the effect on early star formation and on formation of the most
massive object at high redshift. We show that by comparing the effects of
primordial non-Gaussianity on cluster abundance with that on void abundance, we
can distinguish between the skewness and the kurtosis types of primordial
non-Gaussianity. As for early star formation, we show that the kurtosis type of
primordial non-Gaussianity seems not to affect the reionization history of the
Universe on average. However, at high redshifts (up to ) such
non-Gaussianity does somewhat affect the early stages of reionization.Comment: 14 pages, 7 figures, accepted for publication in MNRA
Primordial Non-Gaussianity from a Joint Analysis of Cosmic Microwave Background Temperature and Polarization
We explore a systematic approach to the analysis of primordial
non-Gaussianity using fluctuations in temperature and polarization of the
Cosmic Microwave Background (CMB). Following Munshi & Heavens (2009), we define
a set of power-spectra as compressed forms of the bispectrum and trispectrum
derived from CMB temperature and polarization maps; these spectra compress the
information content of the corresponding full multispectra and can be useful in
constraining early Universe theories. We generalize the standard pseudo-C_l
estimators in such a way that they apply to these spectra involving both spin-0
and spin-2 fields, developing explicit expressions which can be used in the
practical implementation of these estimators. While these estimators are
suboptimal, they are nevertheless unbiased and robust hence can provide useful
diagnostic tests at a relatively small computational cost. We next consider
approximate inverse-covariance weighting of the data and construct a set of
near-optimal estimators based on that approach. Instead of combining all
available information from the entire set of mixed bi- or trispectra, i.e
multispectra describing both temperature and polarization information, we
provide analytical constructions for individual estimators, associated with
particular multispectra. The bias and scatter of these estimators can be
computed using Monte-Carlo techniques. Finally, we provide estimators which are
completely optimal for arbitrary scan strategies and involve inverse covariance
weighting; we present the results of an error analysis performed using a
Fisher-matrix formalism at both the one-point and two-point level.Comment: 25 Pages, 4 Figure
Hip joint replacement based on linear cylindrical articulations for reduced wear : a radical change in design
Hip replacement surgery is a common procedure for patients suffering from hip joint
degeneration. However, wear of the implant components, particularly Ultra-High-Molecular-
Weight Polyethylene (UHMWPE), remains a significant concern, often leading to
complications such as osteolysis and implant loosening. This invention disclosure introduces a
novel tri-axial hip replacement design aimed at addressing these issues. The design
incorporates three orthogonal cylindrical articulations, each providing one rotational degree of
freedom to replicate the natural movements of the hip joint. The prosthesis comprises two
components made from UHMWPE (cup and rotator) and two components made from high-N
stainless steel (flexor and abductor). Each articulation consists of metal-on-polyethylene
bearing couples. Unlike traditional ball-and-socket implants, the novel design limits motion
within each articulation to a single direction, taking advantage of friction-induced UHMWPE
strain hardening. Moreover, cylindrical joints offer a larger contact surface area than their
spherical counterparts, thereby reducing contact stresses. Mid-sized high-fidelity prototypes
underwent wear resistance testing, demonstrating significantly superior performance compared to a commercial ball-and-socket implant of similar size tested in the same conditions.
Moreover, a cadaveric implantation performed by experienced orthopaedic surgeons showed
the implant has good stability even for postures requiring a wide range of motion. This
innovative design represents a promising advancement in hip replacement technology, offering
improved wear resistance and longevity, thus potentially reducing the need for revision
surgeries and enhancing patient outcomes.peer-reviewe
New Optimised Estimators for the Primordial Trispectrum
Cosmic microwave background studies of non-Gaussianity involving higher-order
multispectra can distinguish between early universe theories that predict
nearly identical power spectra. However, the recovery of higher-order
multispectra is difficult from realistic data due to their complex response to
inhomogeneous noise and partial sky coverage, which are often difficult to
model analytically. A traditional alternative is to use one-point cumulants of
various orders, which collapse the information present in a multispectrum to
one number. The disadvantage of such a radical compression of the data is a
loss of information as to the source of the statistical behaviour. A recent
study by Munshi & Heavens (2009) has shown how to define the skew spectrum (the
power spectra of a certain cubic field, related to the bispectrum) in an
optimal way and how to estimate it from realistic data. The skew spectrum
retains some of the information from the full configuration-dependence of the
bispectrum, and can contain all the information on non-Gaussianity. In the
present study, we extend the results of the skew spectrum to the case of two
degenerate power-spectra related to the trispectrum. We also explore the
relationship of these power-spectra and cumulant correlators previously used to
study non-Gaussianity in projected galaxy surveys or weak lensing surveys. We
construct nearly optimal estimators for quick tests and generalise them to
estimators which can handle realistic data with all their complexity in a
completely optimal manner. We show how these higher-order statistics and the
related power spectra are related to the Taylor expansion coefficients of the
potential in inflation models, and demonstrate how the trispectrum can
constrain both the quadratic and cubic terms.Comment: 19 pages, 2 figure
Evolution of fNL to the adiabatic limit
We study inflationary perturbations in multiple-field models, for which zeta
typically evolves until all isocurvature modes decay--the "adiabatic limit". We
use numerical methods to explore the sensitivity of the nonlinear parameter fNL
to the process by which this limit is achieved, finding an appreciable
dependence on model-specific data such as the time at which slow-roll breaks
down or the timescale of reheating. In models with a sum-separable potential
where the isocurvature modes decay before the end of the slow-roll phase we
give an analytic criterion for the asymptotic value of fNL to be large. Other
examples can be constructed using a waterfall field to terminate inflation
while fNL is transiently large, caused by descent from a ridge or convergence
into a valley. We show that these two types of evolution are distinguished by
the sign of the bispectrum, and give approximate expressions for the peak fNL.Comment: v1: 25 pages, plus Appendix and bibliography, 6 figures. v2: minor
edits to match published version in JCA
Higher-order Statistics of Weak Lensing Shear and Flexion
Owing to their more extensive sky coverage and tighter control on systematic
errors, future deep weak lensing surveys should provide a better statistical
picture of the dark matter clustering beyond the level of the power spectrum.
In this context, the study of non-Gaussianity induced by gravity can help
tighten constraints on the background cosmology by breaking parameter
degeneracies, as well as throwing light on the nature of dark matter, dark
energy or alternative gravity theories. Analysis of the shear or flexion
properties of such maps is more complicated than the simpler case of the
convergence due to the spinorial nature of the fields involved. Here we develop
analytical tools for the study of higher-order statistics such as the
bispectrum (or trispectrum) directly using such maps at different source
redshift. The statistics we introduce can be constructed from cumulants of the
shear or flexions, involving the cross-correlation of squared and cubic maps at
different redshifts. Typically, the low signal-to-noise ratio prevents recovery
of the bispectrum or trispectrum mode by mode. We define power spectra
associated with each multi- spectra which compresses some of the available
information of higher order multispectra. We show how these can be recovered
from a noisy observational data even in the presence of arbitrary mask, which
introduces mixing between Electric (E-type) and Magnetic (B-type) polarization,
in an unbiased way. We also introduce higher order cross-correlators which can
cross-correlate lensing shear with different tracers of large scale structures.Comment: 16 pages, 2 figure
Observing the Evolution of the Universe
How did the universe evolve? The fine angular scale (l>1000) temperature and
polarization anisotropies in the CMB are a Rosetta stone for understanding the
evolution of the universe. Through detailed measurements one may address
everything from the physics of the birth of the universe to the history of star
formation and the process by which galaxies formed. One may in addition track
the evolution of the dark energy and discover the net neutrino mass.
We are at the dawn of a new era in which hundreds of square degrees of sky
can be mapped with arcminute resolution and sensitivities measured in
microKelvin. Acquiring these data requires the use of special purpose
telescopes such as the Atacama Cosmology Telescope (ACT), located in Chile, and
the South Pole Telescope (SPT). These new telescopes are outfitted with a new
generation of custom mm-wave kilo-pixel arrays. Additional instruments are in
the planning stages.Comment: Science White Paper submitted to the US Astro2010 Decadal Survey.
Full list of 177 author available at http://cmbpol.uchicago.ed
PRISM (Polarized Radiation Imaging and Spectroscopy Mission): A White Paper on the Ultimate Polarimetric Spectro-Imaging of the Microwave and Far-Infrared Sky
PRISM (Polarized Radiation Imaging and Spectroscopy Mission) was proposed to
ESA in response to the Call for White Papers for the definition of the L2 and
L3 Missions in the ESA Science Programme. PRISM would have two instruments: (1)
an imager with a 3.5m mirror (cooled to 4K for high performance in the
far-infrared---that is, in the Wien part of the CMB blackbody spectrum), and
(2) an Fourier Transform Spectrometer (FTS) somewhat like the COBE FIRAS
instrument but over three orders of magnitude more sensitive. Highlights of the
new science (beyond the obvious target of B-modes from gravity waves generated
during inflation) made possible by these two instruments working in tandem
include: (1) the ultimate galaxy cluster survey gathering 10e6 clusters
extending to large redshift and measuring their peculiar velocities and
temperatures (through the kSZ effect and relativistic corrections to the
classic y-distortion spectrum, respectively) (2) a detailed investigation into
the nature of the cosmic infrared background (CIB) consisting of at present
unresolved dusty high-z galaxies, where most of the star formation in the
universe took place, (3) searching for distortions from the perfect CMB
blackbody spectrum, which will probe a large number of otherwise inaccessible
effects (e.g., energy release through decaying dark matter, the primordial
power spectrum on very small scales where measurements today are impossible due
to erasure from Silk damping and contamination from non-linear cascading of
power from larger length scales). These are but a few of the highlights of the
new science that will be made possible with PRISM.Comment: 20 pages Late
Unpublished Mediterranean records of marine alien and cryptogenic species
Good datasets of geo-referenced records of alien species are a prerequisite for assessing the spatio-temporal dynamics of biological invasions, their invasive potential, and the magnitude of their impacts. However, with the exception of first records on a country level or wider regions, observations of species presence tend to remain unpublished, buried in scattered repositories or in the personal databases of experts. Through an initiative to collect, harmonize and make such unpublished data for marine alien and cryptogenic species in the Mediterranean Sea available, a large dataset comprising 5376 records was created. It includes records of 239 alien or cryptogenic taxa (192 Animalia, 24 Plantae, 23 Chromista) from 19 countries surrounding the Mediterranean Sea. In terms of records, the most reported Phyla in descending order were Chordata, Mollusca, Chlorophyta, Arthropoda, and Rhodophyta. The most recorded species was Caulerpa cylindracea, followed by Siganus luridus, Magallana sp. (cf. gigas or angulata) and Pterois miles. The dataset includes records from 1972 to 2020, with the highest number of records observed in 2018. Among the records of the dataset, Dictyota acutiloba is a first record for the Mediterranean Sea. Nine first country records are also included: the alga Caulerpa taxifolia var. distichophylla, the cube boxfish Ostracion cubicus, and the cleaner shrimp Urocaridella pulchella from Israel; the sponge Paraleucilla magna from Libya and Slovenia; the lumpfish Cyclopterus lumpus from Cyprus; the bryozoan Celleporaria vermiformis and the polychaetes Prionospio depauperata and Notomastus aberans from Malta
Exploring Cosmic Origins with CORE: Cosmological Parameters
We forecast the main cosmological parameter constraints achievable with theCORE space mission which is dedicated to mapping the polarisation of the CosmicMicrowave Background (CMB). CORE was recently submitted in response to ESA'sfifth call for medium-sized mission proposals (M5). Here we report the resultsfrom our pre-submission study of the impact of various instrumental options, inparticular the telescope size and sensitivity level, and review the great,transformative potential of the mission as proposed. Specifically, we assessthe impact on a broad range of fundamental parameters of our Universe as afunction of the expected CMB characteristics, with other papers in the seriesfocusing on controlling astrophysical and instrumental residual systematics. Inthis paper, we assume that only a few central CORE frequency channels areusable for our purpose, all others being devoted to the cleaning ofastrophysical contaminants. On the theoretical side, we assume LCDM as ourgeneral framework and quantify the improvement provided by CORE over thecurrent constraints from the Planck 2015 release. We also study the jointsensitivity of CORE and of future Baryon Acoustic Oscillation and Large ScaleStructure experiments like DESI and Euclid. Specific constraints on the physicsof inflation are presented in another paper of the series. In addition to thesix parameters of the base LCDM, which describe the matter content of aspatially flat universe with adiabatic and scalar primordial fluctuations frominflation, we derive the precision achievable on parameters like thosedescribing curvature, neutrino physics, extra light relics, primordial heliumabundance, dark matter annihilation, recombination physics, variation offundamental constants, dark energy, modified gravity, reionization and cosmicbirefringence. (ABRIDGED
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