388 research outputs found
Reducing sample variance: halo biasing, non-linearity and stochasticity
Comparing clustering of differently biased tracers of the dark matter
distribution offers the opportunity to reduce the cosmic variance error in the
measurement of certain cosmological parameters. We develop a formalism that
includes bias non-linearities and stochasticity. Our formalism is general
enough that can be used to optimise survey design and tracers selection and
optimally split (or combine) tracers to minimise the error on the
cosmologically interesting quantities. Our approach generalises the one
presented by McDonald & Seljak (2009) of circumventing sample variance in the
measurement of . We analyse how the bias, the noise,
the non-linearity and stochasticity affect the measurements of and explore
in which signal-to-noise regime it is significantly advantageous to split a
galaxy sample in two differently-biased tracers. We use N-body simulations to
find realistic values for the parameters describing the bias properties of dark
matter haloes of different masses and their number density.
We find that, even if dark matter haloes could be used as tracers and
selected in an idealised way, for realistic haloes, the sample variance limit
can be reduced only by up to a factor .
This would still correspond to the gain from a three times larger survey volume
if the two tracers were not to be split. Before any practical application one
should bear in mind that these findings apply to dark matter haloes as tracers,
while realistic surveys would select galaxies: the galaxy-host halo relation is
likely to introduce extra stochasticity, which may reduce the gain further.Comment: 21 pages, 13 figures. Published version in MNRA
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: RSD measurement from the power spectrum and bispectrum of the DR12 BOSS galaxies
We measure and analyse the bispectrum of the final, Data Release 12, galaxy
sample provided by the Baryon Oscillation Spectroscopic Survey, splitting by
selection algorithm into LOWZ and CMASS galaxies. The LOWZ sample contains
361\,762 galaxies with an effective redshift of , and the
CMASS sample 777\,202 galaxies with an effective redshift of . Combining the power spectrum, measured relative to the
line-of-sight, with the spherically averaged bispectrum, we are able to
constrain the product of the growth of structure parameter, , and the
amplitude of dark matter density fluctuations, , along with the
geometric Alcock-Paczynski parameters, the product of the Hubble constant and
the comoving sound horizon at the baryon drag epoch, , and the
angular distance parameter divided by the sound horizon, .
After combining pre-reconstruction RSD analyses of the power spectrum monopole,
quadrupole and bispectrum monopole; with post-reconstruction analysis of the
BAO power spectrum monopole and quadrupole, we find , , for
the LOWZ sample, and ,
, for the CMASS sample. We
find general agreement with previous BOSS DR11 and DR12 measurements. Combining
our dataset with {\it Planck15} we perform a null test of General Relativity
(GR) through the -parametrisation finding
, which is away from the GR
predictions.Comment: 34 pages, 22 figures, 8 tables. Accepted for publication in MNRAS.
Data available at https://sdss3.org//science/boss_publications.ph
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: mock galaxy catalogues for the low-redshift sample
We present one thousand mock galaxy catalogues for the analysis of the Low
Redshift Sample (LOWZ, effective redshift z ~ 10.32) of the Baryon Oscillation
Spectroscopic Survey Data Releases 10 and 11. These mocks have been created
following the PTHalos method of Manera13 et al. (2013) revised to include new
developments. The main improvement is the introduction of a redshift dependence
in the Halo Occupation Distribution in order to account for the change of the
galaxy number density with redshift. These mock catalogues are used in the
analyses of the LOWZ galaxy clustering by the BOSS collaboration.Comment: 10 pages, 8 figure
The Bispectrum of f(R) Cosmologies
In this paper we analyze a suite of cosmological simulations of modified
gravitational action f(R) models, where cosmic acceleration is induced by a
scalar field that acts as a fifth force on all forms of matter. In particular,
we focus on the bispectrum of the dark matter density field on mildly
non-linear scales. For models with the same initial power spectrum, the dark
matter bispectrum shows significant differences for cases where the final dark
matter power spectrum also differs. Given the different dependence on bias of
the galaxy power spectrum and bispectrum, bispectrum measurements can close the
loophole of galaxy bias hiding differences in the power spectrum.
Alternatively, changes in the initial power spectrum can also hide differences.
By constructing LCDM models with very similar final non-linear power spectra,
we show that the differences in the bispectrum are reduced (<4%) and are
comparable with differences in the imperfectly matched power spectra. These
results indicate that the bispectrum depends mainly on the power spectrum and
less sensitively on the gravitational signatures of the f(R) model. This weak
dependence of the matter bispectrum on gravity makes it useful for breaking
degeneracies associated with galaxy bias, even for models beyond general
relativity.Comment: 14 pages, 5 figures, Published in JCA
Testing edible mushrooms to inhibit the pancreatic lipase activity by an in vitro digestion model
This is the peer reviewed version of the following article: Palanisamy, M. Testing edible mushrooms to inhibit the pancreatic lipase activity by an in vitro digestion model (2012) International Journal of Food Science and Technology, 47 (5), pp. 1004-1010., which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.2011.02934.x. This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archivingOne of the strategies in prevention or treatment of obesity is altering metabolism of lipids by inhibition of dietary fat absorption. The extracts obtained with methanol, water and methanol:water (1:1) from 21 mushroom species were screened as potential sources of pancreatic lipase (PL) inhibitors using a standardised in vitro test. Lepiota procera methanol:water (1:1) extracts showed the highest inhibition activity closely followed by Grifola frondosa, Pleurotus eryngii and Lyophyllum shimeji. Other mushroom strains such as Morchella conica, Marasmius oreades, Lentinula edodes, Amanita ponderosa and Boletus edulis also showed a certain inhibitory activity. However, when the PL inhibitory activity was evaluated using an in vitro digestion model mimicking gut conditions, none of the selected mushroom extracts were able to inhibit PL activity. On the contrary, stimulation of the lipase activity levels was observed and it was not due to endogenous mushroom lipases activitiesThe research was supported by the European Union within the 7th framework programme (7FM-PEOPLE-2009-IIF project 251285), ALIBIRD-CM S2009 ⁄AGR-1469 regional program from the Community of Madrid (Spain) and AGL2010-21537 national R+D program from the Spanish Ministry of Science and Innovatio
Spread of the invasive alga Caulerpa racemosa var. cylindracea (Caulerpales, Chlorophyta) along the Mediterranean Coast of the Murcia region (SE Spain)
The aim of this paper was to document the appearance and spread of the green alga Caulerpa racemosa along the coast of Murcia in south–eastern Spain. It was found for the first time in the area in 2005 and over the next two years the number of new sightings increased almost exponentially. In the period 2005–2007 the total surface area colonised by the alga in the region was estimated to be at least 265 ha. Benthic assemblages colonised by the alga were rocky bottoms with photophilic algae, dead P. oceanica rhizomes, infralittoral and circalittoral soft bottoms and maerl beds. No penetration of the alga was observed in P. oceanica meadows, except in one locality. Biometric analysis indicated high vegetative development in the established colonies in comparison to those described in other Mediterranean areas. Rapid spreading dynamics observed in the Murcia region is a potential threat for native benthic communities.
Key words: Biological invasions, Caulerpa racemosa var. cylindracea, Colonised surface area, Distribution, Mediterranean Sea, Spain.En el presente trabajo se documenta la aparición y dispersión del alga verde Caulerpa racemosa a lo largo de la costa de Murcia, región situada en el sureste español. El alga fue detectada por primera vez en el año 2005 y durante los dos años consecutivos se observó un crecimiento casi exponencial en el número de áreas colonizadas. La superficie total colonizada por el alga en Murcia durante el periodo 2005–2007 ha sido estimada en 265 ha., siendo las comunidades bentónicas afectadas algas fotófilas sobre sustrato rocoso, "mata muerta" de P. oceanica, fondos blandos infralitorales y circalitorales y fondos con comunidades de maërl. La presencia del alga dentro de praderas de P. oceanica solamente fue detectada en una localidad. Los estudios biométricos realizados muestran un elevado desarrollo vegetativo de las poblaciones de C. racemosa en Murcia en comparación con colonias de otras áreas del Mediterráneo, siendo esta rápida dinámica de expansión una amenaza potencial para las comunidades bentonicas nativas.
Palabras clave: Invasiones biológicas, Caulerpa racemosa var. cylindracea, Superficie colonizada, Mar
Mediterraneo, España.The aim of this paper was to document the appearance and spread of the green alga Caulerpa racemosa along the coast of Murcia in south–eastern Spain. It was found for the first time in the area in 2005 and over the next two years the number of new sightings increased almost exponentially. In the period 2005–2007 the total surface area colonised by the alga in the region was estimated to be at least 265 ha. Benthic assemblages colonised by the alga were rocky bottoms with photophilic algae, dead P. oceanica rhizomes, infralittoral and circalittoral soft bottoms and maerl beds. No penetration of the alga was observed in P. oceanica meadows, except in one locality. Biometric analysis indicated high vegetative development in the established colonies in comparison to those described in other Mediterranean areas. Rapid spreading dynamics observed in the Murcia region is a potential threat for native benthic communities.
Key words: Biological invasions, Caulerpa racemosa var. cylindracea, Colonised surface area, Distribution, Mediterranean Sea, Spain
Pressurized water extraction of β-glucan enriched fractions with bile acids-binding capacities obtained from edible mushrooms
This is the peer reviewed version of the following article: Biotechnology Progress 30.2 (2014): 391-400, which has been published in final form at http://dx.doi.org/10.1002/btpr.1865. This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archivingA pressurized water extraction (PWE) method was developed in order to extract β-glucans with bile acids-binding capacities from cultivated mushrooms (Agaricus bisporus, Lentinula edodes and Pleurotus ostreatus) to be used as supplements to design novel foods with hypocholesterolemic properties. Extraction yields were higher in individual than sequential extractions being the optimal extraction parameters: 200ºC, 5 cycles of 5 min each at 10.3 MPa. The crude polysaccharide (PSC) fractions, isolated from the PWE extracts contained mainly β-glucans (including chitooligosaccharides deriving from chitin hydrolysis), -glucans and other PSCs (hetero-/proteo-glucans) depending on the extraction temperature and mushroom strain considered. The observed bile acids-binding capacities of some extracts were similar to a β-glucan enriched fraction obtained from cereals.The research was supported by the European Union within the 7th framework programme (7FM-PEOPLE-2009-IIF project 251285), ALIBIRD-CM S2009/AGR-1469 regional program from the Community of Madrid (Spain) and AGL2010-21537 national R+D program from the Spanish Ministry of Science and Innovation. CTICH is also acknowledged for the cultivation and supplying of the mushrooms fruiting bodie
Detection of Baryon Acoustic Oscillation Features in the Large-Scale 3-Point Correlation Function of SDSS BOSS DR12 CMASS Galaxies
We present the large-scale 3-point correlation function (3PCF) of the SDSS
DR12 CMASS sample of Luminous Red Galaxies, the largest-ever sample
used for a 3PCF or bispectrum measurement. We make the first high-significance
() detection of Baryon Acoustic Oscillations (BAO) in the 3PCF.
Using these acoustic features in the 3PCF as a standard ruler, we measure the
distance to to precision (statistical plus systematic). We
find for our
fiducial cosmology (consistent with Planck 2015) and bias model. This
measurement extends the use of the BAO technique from the 2-point correlation
function (2PCF) and power spectrum to the 3PCF and opens an avenue for deriving
additional cosmological distance information from future large-scale structure
redshift surveys such as DESI. Our measured distance scale from the 3PCF is
fairly independent from that derived from the pre-reconstruction 2PCF and is
equivalent to increasing the length of BOSS by roughly 10\%; reconstruction
appears to lower the independence of the distance measurements. Fitting a model
including tidal tensor bias yields a moderate significance (
detection of this bias with a value in agreement with the prediction from local
Lagrangian biasing.Comment: 15 pages, 7 figures, submitted MNRA
An improved fitting formula for the dark matter bispectrum
In this paper we present an improved fitting formula for the dark matter
bispectrum motivated by the previous phenomenological approach of Scoccimarro &
Couchman (2001). We use a set of LCDM simulations to calibrate the fitting
parameters in the k-range of 0.03 h/Mpc<k<0.4 h/Mpc and in the redshift range
of 0<z<1.5. This new proposed fit describes well the BAO-features although it
was not designed to. The deviation between the simulations output and our
analytic prediction is typically less than 5% and in the worst case is never
above 10%. We envision that this new analytic fitting formula will be very
useful in providing reliable predictions for the non-linear dark matter
bispectrum for LCDM models.Comment: 16 pages, 5 figures. Published in JCA
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