Mechanical properties and electrical surface charges of microfibrillated cellulose/imidazole-modified polyketone composite membranes

In the present work, microfibrillated cellulose (MFC) suspensions were produced by high-pressure homogenization and subsequently used to fabricate MFC membranes (C-1) by vacuum filtration followed by hot-pressing. A polyketone (PK50) was chemically modified by Paal-Knorr reaction to graft imidazole (IM) functional groups along its backbone structure. The resulting polymer is referred to as PK50IM80. By solution impregnation, C-1 was immersed in an aqueous solution of PK50IM80 and subsequently hot pressed, resulting in the fabrication of MFC/PK50IM80 composite membranes (C-IMP). Another method, referred to as solution mixing, consisted in adding MFC into an aqueous solution of PK50IM80 followed by vacuum filtration and hot-pressing to obtain MFC/PK50IM80 composite membranes (C-MEZC). C-IMP and C-MEZC were characterized by a wide range of analytical techniques including, X-ray photoelectron spectroscopy, Fourier-transform infrared chemical imaging, scanning electron microscopy, atomic force microscopy, dynamical mechanical analysis, tensile testing as well as streaming zeta potential, and compared to C-1 (reference material). The results suggested that C-IMP possess a more homogeneous distribution of PK50IM80 at their surface compared to C-MEZC. C-IMP was found to possess significantly enhanced Young's modulus compared to C-1 and C-MEZC. The tensile strength of C-IMP was found to improve significantly compared to C-1, whereas C-1 possessed significantly higher tensile index than C-IMP and C-MEZC. Furthermore, the presence of PK50IM80 at the surface of MFC was found to significantly shift the isoelectric point (IEP) of the membranes from pH 2.3 to a maximum value of 4.5 for C-IMP. Above the IEP, C-IMP and C-MEZC were found to possess significantly less negative electrical surface charges (plateau value of -25 mV at pH 10) when compared to C-1 (plateau value of -42 mV at pH 10). Our approach may have implication to broaden the range of filtration applications of MFC-based membranes

Unfolding the Hierarchy of Voids

We present a framework for the hierarchical identification and characterization of voids based on the Watershed Void Finder. The Hierarchical Void Finder is based on a generalization of the scale space of a density field invoked in order to trace the hierarchical nature and structure of cosmological voids. At each level of the hierarchy, the watershed transform is used to identify the voids at that particular scale. By identifying the overlapping regions between watershed basins in adjacent levels, the hierarchical void tree is constructed. Applications on a hierarchical Voronoi model and on a set of cosmological simulations illustrate its potential.Comment: 5 pages, 2 figure

Cosmology and Cluster Halo Scaling Relations

We explore the effects of dark matter and dark energy on the dynamical scaling properties of galaxy clusters. We investigate the cluster Faber-Jackson (FJ), Kormendy and Fundamental Plane (FP) relations between the mass, radius and velocity dispersion of cluster size halos in cosmological $N$-body simulations. The simulations span a wide range of cosmological parameters, representing open, flat and closed Universes. Independently of the cosmology, we find that the simulated clusters are close to a perfect virial state and do indeed define a Fundamental Plane. The fitted parameters of the FJ, Kormendy and FP relationships do not show any significant dependence on $\Omega_m$ and/or $\Omega_{\Lambda}$. The one outstanding effect is the influence of $\Omega_{m}$ on the thickness of the Fundamental Plane. Following the time evolution of our models, we find slight changes of FJ and Kormendy parameters in high $\Omega_m$ universe, along with a slight decrease of FP fitting parameters. We also see an initial increase of the FP thickness followed by a convergence to a nearly constant value. The epoch of convergence is later for higher values of $\Omega_m$ while the thickness remains constant in the low $\Omega_m$ $\Lambda$-models. We also find a continuous increase of the FP thickness in the Standard CDM (SCDM) cosmology. There is no evidence that these differences are due to the different power spectrum slope at cluster scales. From the point of view of the FP, there is little difference between clusters that quietly accreted their mass and those that underwent massive mergers. The principal effect of strong mergers is to change significantly the ratio of the half-mass radius $r_{half}$ to the harmonic mean radius $r_h$.Comment: 24 pages, 17 figures, submitted to MNRA

Morphological Properties of Superclusters of Galaxies

We studied superclusters of galaxies in a volume-limited sample extracted from the Sloan Digital Sky Survey Data Release 7 (SDSS/DR7) and from mock catalogues based on a semi-analytical model of galaxy evolution in the Millenium Simulation. A density field method was applied to a sample of galaxies brighter than $M_r= -21+5 \log h_{100}$ to identify superclusters, taking into account selection and boundary effects. In order to evaluate the influence of threshold density, we have chosen two thresholds: the first maximizes the number of objects (D1), and the second constrains the maximum supercluster size to $\sim$120~h$^{-1}$Mpc (D2). We have performed a morphological analysis, using Minkowski Functionals, based on a parameter which increases monotonically from filaments to pancakes. An anti-correlation was found between supercluster richness (and total luminosity or size) and the morphological parameter, indicating that filamentary structures tend to be richer, larger and more luminous than pancakes in both observed and mock catalogues. We have also used the mock samples to compare supercluster morphologies identified in position and velocity spaces, concluding that our morphological classification is not biased by the peculiar velocities. Monte Carlo simulations designed to investigate the reliability of our results with respect to random fluctuations show that these results are robust. Our analysis indicates that filaments and pancakes present different luminosity and size distributions.Comment: 12 pages, 17 figures Accepted to MNRA

Mass, Light and Colour of the Cosmic Web in the Supercluster SCL2243-0935 (z=0.447)

Context: In 2.2m MPG-ESO/WFI data we discovered several mass peaks through weak lensing, forming a possible supercluster at redshift 0.45. Through multi-colour wide-field imaging with CFHT/Megaprime and INT/WFC we identify early-type galaxies and trace the supercluster network with them. Through EMMI/NTT multi-object spectroscopy we verify the initial shear-selected cluster candidates. Using weak lensing we obtain mass estimates for the supercluster centre and the filaments. Results: We identified the centre of the SCL2243-0935 supercluster, MACS J2243-0935, which was found independently by Ebeling et al. (2010). 13 more clusters or overdensities are embedded in a filamentary network, half of them are already spectroscopically confirmed. Three (5-15) Mpc filaments are detected, and we estimate the global size of SCL2243 to 45x15x50 Mpc, making it one of the largest superclusters known at intermediate redshifts. Weak lensing yields r_200=(2.06+/-0.13) Mpc and M_200=(1.54+/-0.29)x10^15 M_sun for MACS J2243 with M/L=428+/-82, very similar to results from size-richness cluster scaling relations. Integrating the weak lensing surface mass density over the supercluster network (defined by increased i-band luminosity or g-i colours), we find (1.53+/-1.01)x10^15 M_sun and M/L=305+/-201 for the three main filaments, consistant with theoretical predictions. The filaments' projected surface mass density is 0.007-0.012, corresponding to 10-100 times the critical density. The greatly varying density of the cosmic web is also reflected in the mean colour of galaxies. Conclusions: SCL2243 is significantly larger and much more richly structured than other known superclusters such as A901/902 or MS0302 studied with weak lensing before. It is a text-book supercluster with little contamination along the line of sight, making it a perfect sandbox for testing new techniques probing the cosmic web.Comment: 26 pages, 16 figures, accepted for publication Astronomy and Astrophysics. Minor corrections implemented as requested by the refere

Radio Emission in the Cosmic Web

We explore the possibility of detecting radio emission in the \emph{cosmic web} by analyzing shock waves in the MareNostrum cosmological simulation. This requires a careful calibration of shock finding algorithms in Smoothed-Particle Hydrodynamics simulations, which we present here. Moreover, we identify the elements of the cosmic web, namely voids, walls, filaments and clusters with the use of the SpineWeb technique, a procedure that classifies the structure in terms of its topology. Thus, we are able to study the Mach number distribution as a function of its environment. We find that the median Mach number, for clusters is $\mathcal{M}_{\mathrm{clusters}}\approx1.8$, for filaments is $\mathcal{M}_{\mathrm{filaments}}\approx 6.2$, for walls is $\mathcal{M}_{\mathrm{walls}}\approx 7.5$, and for voids is $\mathcal{M}_{\mathrm{voids}}\approx 18$. We then estimate the radio emission in the cosmic web using the formalism derived in Hoeft & Br\"{u}ggen (2007). We also find that in order to match our simulations with observational data (e.g., NVSS radio relic luminosity function), a fraction of energy dissipated at the shock of $\xi_{\mathrm{e}}=0.0005$ is needed, in contrast with the $\xi_{\mathrm{e}}=0.005$ proposed by Hoeft et al. (2008). We find that 41% of clusters with $M \ge 10^{14} M_{\odot}$ host diffuse radio emission in the form of radio relics. Moreover, we predict that the radio flux from filaments should be $S_{150 MHz}\sim 0.12$ $\mu$Jy at a frequency of 150 MHz.Comment: 19 pages, 17 figures, accepted for publication in MNRAS. Minor changes to tex fil

Future Evolution of Bound Superclusters in an Accelerating Universe

The evolution of marginally bound supercluster-like objects in an accelerating LambdaCDM Universe is followed, by means of cosmological simulations, from the present time to an expansion factor a = 100. The objects are identified on the basis of the binding density criterion introduced by Dunner et al. (2006). superclusters are identified with the ones whose mass M > 10^15 M_sun/h, the most massive one with M ~ 8x10^15 M_sun/h, comparable to the Shapley supercluster. The spatial distribution of the superclusters remains essentially the same after the present epoch, reflecting the halting growth of the Cosmic Web as Lambda gets to dominate the expansion of the Universe. The same trend can be seen in the stagnation of the development of the mass function of virialized haloes and bound objects. The situation is considerably different when looking at the internal evolution, quantified in terms of their shape, compactness and density profile, and substructure in terms of their multiplicity function. We find a continuing evolution from a wide range of triaxial shapes at a = 1 to almost perfect spherical shapes at a = 100. We also find a systematic trend towards a higher concentration. Meanwhile, we see their substructure gradually disappearing, as the surrounding subclumps fall in and merge to form one coherent, virialized system.Comment: 27 pages, 17 figures, accepted for publication in MNRAS, revised version after referee repor