1,546 research outputs found
An algorithm for the direct reconstruction of the dark matter correlation function from weak lensing and galaxy clustering
The clustering of matter on cosmological scales is an essential probe for
studying the physical origin and composition of our Universe. To date, most of
the direct studies have focused on shear-shear weak lensing correlations, but
it is also possible to extract the dark matter clustering by combining
galaxy-clustering and galaxy-galaxy-lensing measurements. In this study we
develop a method that can constrain the dark matter correlation function from
galaxy clustering and galaxy-galaxy-lensing measurements, by focusing on the
correlation coefficient between the galaxy and matter overdensity fields. To
generate a mock galaxy catalogue for testing purposes, we use the Halo
Occupation Distribution approach applied to a large ensemble of N-body
simulations to model pre-existing SDSS Luminous Red Galaxy sample observations.
Using this mock catalogue, we show that a direct comparison between the excess
surface mass density measured by lensing and its corresponding galaxy
clustering quantity is not optimal. We develop a new statistic that suppresses
the small-scale contributions to these observations and show that this new
statistic leads to a cross-correlation coefficient that is within a few percent
of unity down to 5 Mpc/h. Furthermore, the residual incoherence between the
galaxy and matter fields can be explained using a theoretical model for
scale-dependent bias, giving us a final estimator that is unbiased to within
1%. We also perform a comprehensive study of other physical effects that can
affect the analysis, such as redshift space distortions and differences in
radial windows between galaxy clustering and weak lensing observations. We
apply the method to a range of cosmological models and show the viability of
our new statistic to distinguish between cosmological models.Comment: 23 pages, 14 figures, accepted by PRD; minor changes to V1, 1 new
figure, more detailed discussion of the covariance of the new ADSD statisti
The SQM/COSMO filter: reliable native pose identification based on the quantum-mechanical description of proteinâligand interactions and implicit COSMO solvation
Current virtual screening tools are fast, but reliable scoring is elusive. Here, we present the "SQM/COSMO filter", a novel scoring function featuring a quantitative semiempirical quantum mechanical (SQM) description of all types of noncovalent interactions coupled with implicit COSMO solvation. We show unequivocally that it outperforms eight widely used scoring functions. The accuracy and chemical generality of the SQM/COSMO filter make it a perfect tool for late stages of virtual screening
Male mate choice scales female ornament allometry in a cichlid fish
<p>Abstract</p> <p>Background</p> <p>Studies addressing the adaptive significance of female ornamentation have gained ground recently. However, the expression of female ornaments in relation to body size, known as trait allometry, still remains unexplored. Here, we investigated the allometry of a conspicuous female ornament in <it>Pelvicachromis taeniatus</it>, a biparental cichlid that shows mutual mate choice and ornamentation. Females feature an eye-catching pelvic fin greatly differing from that of males.</p> <p>Results</p> <p>We show that allometry of the female pelvic fin is scaled more positively in comparison to other fins. The pelvic fin exhibits isometry, whereas the other fins (except the caudal fin) show negative allometry. The size of the pelvic fin might be exaggerated by male choice because males prefer female stimuli that show a larger extension of the trait. Female pelvic fin size is correlated with individual condition, suggesting that males can assess direct and indirect benefits.</p> <p>Conclusions</p> <p>The absence of positive ornament allometry might be a result of sexual selection constricted by natural selection: fins are related to locomotion and thus may be subject to viability selection. Our study provides evidence that male mate choice might scale the expression of a female sexual ornament, and therefore has implications for the understanding of the relationship of female sexual traits with body size in species with conventional sex-roles.</p
Impact of anion polarizability on ion pairing in microhydrated salt clusters
Despite longstanding interest in the mechanism of salt dissolution in aqueous media, a molecular level understanding remains incomplete. Here, cryogenic ion trap vibrational action spectroscopy is combined with electronic structure calculations to track salt hydration in a gas phase model system one water molecule at a time. The infrared photodissociation spectra of microhydrated lithium dihalide anions [LiXXâ˛(H2O)n]- (XXⲠ= I2, ClI and Cl2; n = 1â3) in the OH stretching region (3800â2800 cm-1) provide a detailed picture of how anion polarizability influences the competition among ionâion, ionâwater and waterâwater interactions. While exclusively contact ion pairs are observed for n = 1, the formation of solvent-shared ion pairs, identified by markedly red-shifted OH stretching bands (-1), originating from the bridging water molecules, is favored already for n = 2. For n = 3, Li+ reaches its maximum coordination number of four only in [LiI2(H2O)3]-, in accordance with the hard and soft Lewis acid and base principle. Waterâwater hydrogen bond formation leads to a different solvent-shared ion pair motif in [LiI2(H2O)3]- and network formation even restabilizes the contact ion pair motif in [LiCl2(H2O)3]-. Structural assignments are exclusively possible after the consideration of anharmonic effects. Molecular dynamics simulations confirm that the significance of large amplitude motion (of the water molecules) increases with increasing anion polarizability and that needs to be considered already at cryogenic temperatures
Beyond the plane-parallel and Newtonian approach: Wide-angle redshift distortions and convergence in general relativity
We extend previous analyses of wide-angle correlations in the galaxy power
spectrum in redshift space to include all general relativistic effects. These
general relativistic corrections to the standard approach become important on
large scales and at high redshifts, and they lead to new terms in the
wide-angle correlations. We show that in principle the new terms can produce
corrections of nearly 10 % on Gpc scales over the usual Newtonian
approximation. General relativistic corrections will be important for future
large-volume surveys such as SKA and Euclid, although the problem of cosmic
variance will present a challenge in observing this.Comment: 14 pages, 5 figures; Typo in equation 5 corrected; results unaffecte
Chronology of dune development in the White River Badlands, northern Great Plains, USA
Aeolian dune field chronologies provide important information on drought history on the Great Plains. The White River Badlands (WRB) dunes are located approximately 60 km north of the Nebraska Sand Hills (NSH), in the western section of the northern Great Plains. Clifftop dunes, sand sheets, and stabilized northwest-southeast trending parabolic dunes are found on upland mesas and buttes, locally called tables. The result of this study is a dune stabilization history determined from samples collected from stratigraphic exposures and dune crests. Thirty-seven OSL ages, from this and previous investigations, show three periods of dune activity: 1) ~21,000 years ago to 12,000 years ago (a), 2) ~9 to 6 ka, and 3) post-700 a. Stratigraphic exposures and low-relief dune forms preserve evidence of late Pleistocene and middle Holocene dune development, while high-relief dune crests preserve evidence of late Holocene dune development. Results of 12 OSL ages from the most recent dune activation event indicate that Medieval Climate Anomaly (MCA) droughts and Little Ice Age (LIA) droughts caused dune reactivation on the tables. Dune reactivation was accompanied by other drought-driven geomorphological responses in the WRB, including fluvial incision of the prairie and formation of sod tables. Regional significance of the MCA and LIA droughts is supported by similarities in the aeolian chronologies of the NSH at 700â600 a and some western Great Plains dune fields at 420â210 a. Aerial photographs of the WRB show little activity during the Dust Bowl droughts of the 1930s
Bias, redshift space distortions and primordial nongaussianity of nonlinear transformations: application to Lyman alpha forest
On large scales a nonlinear transformation of matter density field can be
viewed as a biased tracer of the density field itself. A nonlinear
transformation also modifies the redshift space distortions in the same limit,
giving rise to a velocity bias. In models with primordial nongaussianity a
nonlinear transformation generates a scale dependent bias on large scales. We
derive analytic expressions for these for a general nonlinear transformation.
These biases can be expressed entirely in terms of the one point distribution
function (PDF) of the final field and the parameters of the transformation. Our
analysis allows one to devise nonlinear transformations with nearly arbitrary
bias properties, which can be used to increase the signal in the large scale
clustering limit. We apply the results to the ionizing equilibrium model of
Lyman-alpha forest, in which Lyman-alpha flux F is related to the density
perturbation delta via a nonlinear transformation. Velocity bias can be
expressed as an average over the Lyman-alpha flux PDF. At z=2.4 we predict the
velocity bias of -0.1, compared to the observed value of -0.13 +/- 0.03. Bias
and primordial nongaussianity bias depend on the parameters of the
transformation. Measurements of bias can thus be used to constrain these
parameters, and for reasonable values of the ionizing background intensity we
can match the predictions to observations. Matching to the observed values we
predict the ratio of primordial nongaussianity bias to bias to have the
opposite sign and lower magnitude than the corresponding values for the highly
biased galaxies, but this depends on the model parameters and can also vanish
or change the sign.Comment: 18 pages, 1 figur
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