7,177 research outputs found
Primordial Non-Gaussianity and the NRAO VLA Sky Survey
The NRAO VLA Sky Survey (NVSS) is the only dataset that allows an accurate
determination of the auto-correlation function (ACF) on angular scales of
several degrees for Active Galactic Nuclei (AGNs) at typical redshifts . Surprisingly, the ACF is found to be positive on such large scales
while, in the framework of the standard hierarchical clustering scenario with
Gaussian primordial perturbations it should be negative for a
redshift-independent effective halo mass of order of that found for
optically-selected quasars. We show that a small primordial non-Gaussianity can
add sufficient power on very large scales to account for the observed NVSS ACF.
The best-fit value of the parameter , quantifying the amplitude of
primordial non-Gaussianity of local type is (
error bar) and ( confidence level),
corresponding to a detection of non-Gaussianity significant at the confidence level. The minimal halo mass of NVSS sources is found to
be () strikingly
close to that found for optically selected quasars. We discuss caveats and
possible physical and systematic effects that can impact on the results.Comment: 6 pages, 5 figure
Deployable robotic woven wire structures and joints for space applications
Deployable robotic structures are basically expandable and contractable structures that may be transported or launched to space in a compact form. These structures may then be intelligently deployed by suitable actuators. The deployment may also be done by means of either airbag or spring-loaded typed mechanisms. The actuators may be pneumatic, hydraulic, ball-screw type, or electromagnetic. The means to trigger actuation may be on-board EPROMS, programmable logic controllers (PLCs) that trigger actuation based on some input caused by the placement of the structure in the space environment. The actuation may also be performed remotely by suitable remote triggering devices. Several deployable woven wire structures are examined. These woven wire structures possess a unique form of joint, the woven wire joint, which is capable of moving and changing its position and orientation with respect to the structure itself. Due to the highly dynamic and articulate nature of these joints the 3-D structures built using them are uniquely and highly expandable, deployable, and dynamic. The 3-D structure naturally gives rise to a new generation of deployable three-dimensional spatial structures
Difficult Environments : Bridging Concepts and Practice for Low Carbon Climate Resilient Development
Testing the Warm Dark Matter paradigm with large-scale structures
We explore the impact of a LWDM cosmological scenario on the clustering
properties of large-scale structure in the Universe. We do this by extending
the halo model. The new development is that we consider two components to the
mass density: one arising from mass in collapsed haloes, and the second from a
smooth component of uncollapsed mass. Assuming that the nonlinear clustering of
dark matter haloes can be understood, then from conservation arguments one can
precisely calculate the clustering properties of the smooth component and its
cross-correlation with haloes. We then explore how the three main ingredients
of the halo calculations, the mass function, bias and density profiles are
affected by WDM. We show that, relative to CDM: the mass function is suppressed
by ~50%, for masses ~100 times the free-streaming mass-scale; the bias of low
mass haloes can be boosted by up to 20%; core densities of haloes can be
suppressed. We also examine the impact of relic thermal velocities on the
density profiles, and find that these effects are constrained to scales r<1
kpc/h, and hence of little importance for dark matter tests, owing to
uncertainties in the baryonic physics. We use our modified halo model to
calculate the non-linear matter power spectrum, and find significant
small-scale power in the model. However, relative to the CDM case, the power is
suppressed. We then calculate the expected signal and noise that our set of
LWDM models would give for a future weak lensing mission. We show that the
models should in principle be separable at high significance. Finally, using
the Fisher matrix formalism we forecast the limit on the WDM particle mass for
a future full-sky weak lensing mission like Euclid or LSST. With Planck priors
and using multipoles l<5000, we find that a lower limit of 2.6 keV should be
easily achievable.Comment: Replaced with version accepted for publication in PRD. Inclusion of:
new figure showing dependence of predictions on cut-off mass; new discussion
of mass function; updated refs. 18 pages, 10 Figure
Challenges to optimal medicines use in people living with dementia and their caregivers: A literature review
Dementia is fast becoming a global concern due to a demographic shift towards an older population. Many studies have shown that caring for a family member or friend has a profound and negative impact on the physical, emotional and psychosocial aspects of the caregivers’ life. One significant activity that a family caregiver undertakes is assistance with the management of medicines. This review was undertaken to ascertain what the issues are that affect optimal medicines use from the perspectives of people living with dementia and their caregivers, both in the community and care home settings. A literature search was conducted using electronic databases, employing a combination of search terms. A total of 16 studies met the inclusion criteria. Six broad themes were identified, together with some recommendations to improve medicines use in people with dementia. Challenges to medicines use centred on medicines management and administration, the impact on the caregiver and care recipient, their partnership and interface with formal care. Future research should focus on developing targeted interventions that can overcome these challenges to achieve optimal medicines use
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
Poly[[bis(μ2-4,4′-bipyridine)[μ2-(2,4-dichlorophenoxy)acetato]copper(I)] nitrate]
The title compound, {[Cu2(C8H5Cl2O3)(C10H8N2)2]NO3}n was prepared by reacting copper(II) nitrate with 4,4′-bipyridine (4,4′-bipy) and (2,4-dichlorophenoxy)acetic acid under solvothermal conditions. Each of two copper(I) atoms in the asymmetric unit is three-coordinated by two N atoms from two 4,4′-bipy ligands and one O atom from the (2,4-dichlorophenoxy)acetate ligand. As both ligands act as bridging ligands, a double-stranded chain structure is observed
Primordial non-Gaussianity, scale-dependent bias, and the bispectrum of galaxies
We calculate the bispectrum, B_g(k_1,k_2,k_3), Fourier transform of the
three-point function of density peaks (e.g., galaxies), using two different
methods: the Matarrese-Lucchin-Bonometto formula and the locality of galaxy
bias. The bispectrum of peaks is not only sensitive to that of the underlying
matter density fluctuations, but also to the four-point function. For a
physically-motivated, local form of primordial non-Gaussianity in the curvature
perturbation, we show that the galaxy bispectrum contains five physically
distinct pieces: (i) non-linear gravitational evolution, (ii) non-linear galaxy
bias, (iii) f_nl, (iv) f_nl^2, and (v) \gnl. While (i), (ii), and a part of
(iii) have been derived in the literature, (iv) and (v) are derived in this
paper for the first time. Our finding suggests that the galaxy bispectrum is
more sensitive to f_nl than previously recognized, and is also sensitive to a
new term, g_nl. For a more general form of local-type non-Gaussianity, the
coefficient \fnl^2 can be interpreted as \tau_nl, which allows us to test
multi-field inflation models. The usual terms from Gaussian initial conditions,
have the smallest signals in the squeezed configurations, while the others have
the largest signals; thus, we can distinguish them easily. We cannot interpret
the effects of f_nl on B_g(k_1,k_2,k_3) as a scale-dependent bias, and thus
replacing the linear bias in the galaxy bispectrum with the scale-dependent
bias known for the power spectrum results in an incorrect prediction. As the
importance of primordial non-Gaussianity relative to the non-linear gravity
evolution and galaxy bias increases toward higher redshifts, galaxy surveys
probing a high-redshift universe are particularly useful for probing the
primordial non-Gaussianity.Comment: (v2) 22 pages, 14 figures. Significantly expanded by adding an
alternative derivation of the same result, the next-to-leading order
contributions of the trispectrum, analytical estimations of the magnitude of
the effects, and a comment on tau_NL. Submitted to Ap
Modelling large-scale halo bias using the bispectrum
We study the relation between the halo and matter density fields -- commonly
termed bias -- in the LCDM framework. In particular, we examine the local model
of biasing at quadratic order in the matter density. This model is
characterized by parameters b_1 and b_2. Using an ensemble of N-body
simulations, we apply several statistical methods to estimate the parameters.
We measure halo and matter fluctuations smoothed on various scales and find
that the parameters vary with smoothing scale. We argue that, for real-space
measurements, owing to the mixing of wavemodes, no scale can be found for which
the parameters are independent of smoothing. However, this is not the case in
Fourier space. We measure halo power spectra and construct estimates for an
effective large-scale bias. We measure the configuration dependence of the halo
bispectra B_hhh and reduced bispectra Q_hhh for very large-scale k-space
triangles. From this we constrain b_1 and b_2. Using the lowest-order
perturbation theory, we find that for B_hhh the best-fit parameters are in
reasonable agreement with one another as the triangle scale is varied, but that
the fits become poor as smaller scales are included. The same is true for
Q_hhh. The best-fit parameters depend on the discreteness correction. This led
us to consider halo-mass cross-bispectra. The results from these statistics
support our earlier findings. We develop a test to explore the importance of
missing higher-order terms in the models. We prove that low-order expansions
are not able to correctly model the data, even on scales k_1~0.04 h/Mpc. If
robust inferences are to be drawn from galaxy surveys, then accurate models for
the full nonlinear matter bispectrum and trispectrum will be essential.Comment: 23 pages, 7 figures; accepted for publication in MNRA
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