The Cluster Distribution as a Test of Dark Matter Models. IV: Topology and Geometry

We study the geometry and topology of the large-scale structure traced by galaxy clusters in numerical simulations of a box of side 320 $h^{-1}$ Mpc, and compare them with available data on real clusters. The simulations we use are generated by the Zel'dovich approximation, using the same methods as we have used in the first three papers in this series. We consider the following models to see if there are measurable differences in the topology and geometry of the superclustering they produce: (i) the standard CDM model (SCDM); (ii) a CDM model with $\Omega_0=0.2$ (OCDM); (iii) a CDM model with a `tilted' power spectrum having $n=0.7$ (TCDM); (iv) a CDM model with a very low Hubble constant, $h=0.3$ (LOWH); (v) a model with mixed CDM and HDM (CHDM); (vi) a flat low-density CDM model with $\Omega_0=0.2$ and a non-zero cosmological $\Lambda$ term ($\Lambda$CDM). We analyse these models using a variety of statistical tests based on the analysis of: (i) the Euler-Poincar\'{e} characteristic; (ii) percolation properties; (iii) the Minimal Spanning Tree construction. Taking all these tests together we find that the best fitting model is $\Lambda$CDM and, indeed, the others do not appear to be consistent with the data. Our results demonstrate that despite their biased and extremely sparse sampling of the cosmological density field, it is possible to use clusters to probe subtle statistical diagnostics of models which go far beyond the low-order correlation functions usually applied to study superclustering.Comment: 17 pages, 7 postscript figures, uses mn.sty, MNRAS in pres

Optical altimeter receiver systems study and design for a spaceborne laser altimeter

Design and specifications for optical altimeter receiver system

Nonlinear stochastic biasing from the formation epoch distribution of dark halos

We propose a physical model for nonlinear stochastic biasing of one-point statistics resulting from the formation epoch distribution of dark halos. In contrast to previous works on the basis of extensive numerical simulations, our model provides for the first time an analytic expression for the joint probability function. Specifically we derive the joint probability function of halo and mass density contrasts from the extended Press-Schechter theory. Since this function is derived in the framework of the standard gravitational instability theory assuming the random-Gaussianity of the primordial density field alone, we expect that the basic features of the nonlinear and stochastic biasing predicted from our model are fairly generic. As representative examples, we compute the various biasing parameters in cold dark matter models as a function of a redshift and a smoothing length. Our major findings are (1) the biasing of the variance evolves strongly as redshift while its scale-dependence is generally weak and a simple linear biasing model provides a reasonable approximation roughly at R\simgt 2(1+z)\himpc, and (2) the stochasticity exhibits moderate scale-dependence especially on R\simlt 20\himpc, but is almost independent of $z$. Comparison with the previous numerical simulations shows good agreement with the above behavior, indicating that the nonlinear and stochastic nature of the halo biasing is essentially understood by taking account of the distribution of the halo mass and the formation epoch.Comment: 34 pages, 11 figures, ApJ (2000) in pres

Computational Study of Turbulent-Laminar Patterns in Couette Flow

Turbulent-laminar patterns near transition are simulated in plane Couette flow using an extension of the minimal flow unit methodology. Computational domains are of minimal size in two directions but large in the third. The long direction can be tilted at any prescribed angle to the streamwise direction. Three types of patterned states are found and studied: periodic, localized, and intermittent. These correspond closely to observations in large aspect ratio experiments.Comment: 4 pages, 5 figure

A low CMB variance in the WMAP data

We have estimated the CMB variance from the three-year WMAP data, finding a value which is significantly lower than the one expected from Gaussian simulations using the WMAP best-fit cosmological model, at a significance level of 98.7 per cent. This result is even more prominent if we consider only the north ecliptic hemisphere (99.8 per cent). Different analyses have been performed in order to identify a possible origin for this anomaly. In particular we have studied the behaviour of single radiometers and single year data as well as the effect of residual foregrounds and 1/f noise, finding that none of these possibilities can explain the low value of the variance. We have also tested the effect of varying the cosmological parameters, finding that the estimated CMB variance tends to favour higher values of $n_s$ than the one of the WMAP best-fit model. In addition, we have also tested the consistency between the estimated CMB variance and the actual measured CMB power spectrum of the WMAP data, finding a strong discrepancy. A possible interpretation of this result could be a deviation from Gaussianity and/or isotropy of the CMB.Comment: 13 pages, 5 figures. Some new tests added. Section 5 largely modified. Accepted for publication in MNRA

Induced Shrinkage and Structural Reorganisation in Ammonia-Treated Wood of Corsican Pine

The ammonia-induced shrinkage of Corsican pine wood (Pinus nigra var. calabrica) was determined over a wide range of temperature, from the melting point (-78 C) to above the critical temperature (132 C) of liquid anhydrous ammonia. The swelling of wood was also measured but over a slightly more limited temperature range. The observed swelling and induced shrinkage of wood are explained in terms of two principal mechanisms: crimping and internal swelling of latewood and collapse of earlywood fibres. Confirmation of these mechanisms was provided by electron microscopy studies. Wood is most effectively plasticized between -5 and -33 C and this would seem to be the optimum temperature range for treating wood

Optimisation of waste vegetable oil-based thermoset polymers

Bio-based thermoset polymers were produced from epoxidized waste vegetable oils cured with anhydrides at different molar ratios. Properties were compared to analogues produced with neat oil and DGEBA as a feedstock. Thermal stability proved to be affected by the molar ratio, and the use of feedstock from waste oil resulted in no effect on this property. DMA has shown that higher concentrations of anhydride enhance the storage modulus, Tg (up to 42.5 °C) and crosslink density. The frying process proved to play a minor role in tuning the dynamic-mechanical properties. However, the contribution of the anhydride demonstrated to be significant enough to mitigate the losses caused by the waste oil, as shown statistically in a DOE study. All formulations were chemically resistant to aqueous, organic and acidic media. The identification of the effects of critical parameters on the properties of WVO-based thermosets enables further production of polymers from waste streams

Stochastic Biasing and Weakly Non-linear Evolution of Power Spectrum

Distribution of galaxies may be a biased tracer of the dark matter distribution and the relation between the galaxies and the total mass may be stochastic, non-linear and time-dependent. Since many observations of galaxy clustering will be done at high redshift, the time evolution of non-linear stochastic biasing would play a crucial role for the data analysis of the future sky surveys. In this paper, we develop the weakly non-linear analysis and attempt to clarify the non-linear feature of the stochastic biasing. We compute the one-loop correction of the power spectrum for the total mass, the galaxies and their cross correlation. Assuming the local functional form for the initial galaxy distribution, we investigate the time evolution of the biasing parameter and the correlation coefficient. On large scales, we first find that the time evolution of the biasing parameter could deviate from the linear prediction in presence of the initial skewness. However, the deviation can be reduced when the initial stochasticity exists. Next, we focus on the quasi-linear scales, where the non-linear growth of the total mass becomes important. It is recognized that the scale-dependence of the biasing dynamically appears and the initial stochasticity could affect the time evolution of the scale-dependence. The result is compared with the recent N-body simulation that the scale-dependence of the halo biasing can appear on relatively large scales and the biasing parameter takes the lower value on smaller scales. Qualitatively, our weakly non-linear results can explain this trend if the halo-mass biasing relation has the large scatter at high redshift.Comment: 29pages, 7 postscript figures, submitted to Ap

Sustainable alternative composites using waste vegetable oil based resins

Laminates were produced with epoxy resins from waste vegetable oil (WVO) intended for the manufacturing of environmentally-friendly alternatives for the composites industry. Post-use cooking oil appears a promising source of triglycerides for polymer manufacturing. Matrices cured with methylhexahydrophthalic anhydride (MHHPA) were reinforced with glass and flax fibres, creating a library of composites that were compared to analogues from virgin oil and benchmarked against commercial diglycidyl ether of bisphenol A (DGEBA). Glass fibre-reinforced composites presented Young’s moduli similar to the benchmark but reduced tensile strength. Chemical pre-treatment of the flax fibre (NaOH and stearic acid) countered the limited tensile performance observed for materials with untreated flax; improvements were evidenced by DMA and SEM. Moreover, WVO-based resins greatly improved impact properties and reduced density with no effect on thermal stability. Therefore, WVO-based composites appear as more sustainable alternatives in applications demanding toughness, stiffness and lightweight over strength

The progression of primary bud necrosis in the grapevine cv. Shiraz (Vitis vinifera L.): A histological analysis

Primary Bud Necrosis (PBN) is a physiological disorder occurring in the compound axillary buds of grapevines. PBN causes the axillary bud to senesce and in some cases secondary buds can also abort. Since PBN is common in the grapevine variety Shiraz the aim of this study was to characterise anatomical changes at different stages of PBN development in this cultivar. Grapevine buds were collected from a vineyard located at Charleston, South Australia, Australia. Buds were dissected, assessed for the presence of PBN and rated on severity of the disorder. Buds at various stages of PBN were fixed for light microscopy. Cell breakdown was observed in all buds where PBN was visible. Collapse and thickening of cell walls was observed in a region of necrotic tissue and severity of PBN appeared to increase over time. The location of cell breakdown due to PBN appeared to be random and was not isolated to one region within the primary bud. PBN appeared to stop primordial growth, with cells differentiating further and maturing more rapidly without forming whole leaves. This cell region then breaks down and the necrosis can extend into the secondary buds.