Testing the Distance-Duality Relation with a Combination of Cosmological Distance Observations

In this paper, we propose an accurate test of the distance-duality (DD) relation, $\eta=D_{L}(z)(1+z)^{-2}/D_{A}(z)=1$ (where $D_{L}$ and $D_{A}$ are the luminosity distances and angular diameter distances, respectively), with a combination of cosmological observational data of Type Ia Supernave (SNe Ia) from Union2 set and the galaxy cluster sample under an assumption of spherical model. In order to avoid bias brought by redshift incoincidence between observational data and to consider redshift error bars of both clusters and SNe Ia in analysis, we carefully choose the SNe Ia points which have the minimum acceptable redshift difference of the galaxy cluster sample ($|\Delta z|_{\rm min} =\sigma_{z, \rm SN}+\sigma_{z, \rm cluster}$). By assuming $\eta$ a constant and functions of the redshift parameterized by six different expressions, we find that there exists no conceivable evidence for variations in the DD relation concerning with observational data, since it is well satisfied within $1\sigma$ confidence level for most cases. Further considering different values of $\Delta z$ in constraining, we also find that the choosing of $\Delta z$ may play an important role in this model-independent test of the distance-duality relation for the spherical sample of galaxy clusters.Comment: 9 pages, 4 figures, 1 table. accepted for publication in Res. Astron. Astrophy

Constraints on cosmological models from lens redshift data

Strong lensing has developed into an important astrophysical tool for probing both cosmology and galaxies (their structures, formations, and evolutions). Now several hundreds of strong lens systems produced by massive galaxies have been discovered, which may form well-defined samples useful for statistical analyses. To collect a relatively complete lens redshift data from various large systematic surveys of gravitationally lensed quasars and check the possibility to use it as a future complementarity to other cosmological probes. We use the distribution of gravitationally-lensed image separations observed in the Cosmic Lens All-Sky Survey (CLASS), the PMN-NVSS Extragalactic Lens Survey (PANELS), the Sloan Digital Sky Survey (SDSS) and other surveys, considering a singular isothermal ellipsoid (SIE) model for galactic potentials as well as improved new measurements of the velocity dispersion function of galaxies based on the SDSS DR5 data and recent semi-analytical modeling of galaxy formation, to constrain two dark energy models ($\Lambda$CDM and constant $w$) under a flat universe assumption. We find that the current lens redshift data give a relatively weak constraint on the model parameters. However, by combing the redshift data with the baryonic acoustic oscillation peak and the comic macrowave background data, we obtain more stringent results, which show that the flat $\Lambda$ CDM model is still included at 1$\sigma$.Comment: 18 pages, 6 figures, 1 table, A&A accepte

Rational Synthesis to Optimize Ruthenium-Based Biomass Conversion Catalysts

With worldwide petroleum resources dwindling and greenhouse gas emissions rising, it is urgent to find renewable replacements for petroleum-derived products. A biomass-derived chemical with high potential as a platform intermediate, γ-valerolactone (GVL) can be readily synthesized by hydrogenation of levulinic acid (LA), itself a common biomass intermediate, using supported Ru catalysts. Overall, vapor phase hydrogenation is more energy sensitive as the higher boiling point of LA (~245°C) and requires a high energy input, comparable to liquid phase hydrogenation, which is more economical. To date the literature on many novel biomass conversion processes such as the hydrogenation of LA to GVL has focused more on the process and less on the catalyst. Therefore, many efforts have been given to develop the novel catalysts, to improve the activity, selectivity and stability for the hydrogenation of LA to GVL. The purpose of this dissertation is to systematically study the effects of nanoparticle size, support, dopants including alkali metal, alkaline earth metal and Rhenium on ruthenium activity on the levulinic acid (LA) hydrogenation to γ- valeroactone (GVL), which could provides insight into optimizing commercial process for hydrogenation of LA to GVL by studying the structure-function relationships. The reactions were evaluated in a stainless steel EZE-Seal batch reactor with 100ml capacity. The first part of this work is to derive fundamental synthesis-structure-function relationships of Ru catalysts for LA hydrogenation using carbon and alumina supported Ru nanoparticles which have been synthesized in a rational, repeatable, scalable way. We have demonstrated that the method of strong electrostatic adsorption (SEA) yields well dispersed, homogeneously distributed Ru particles with tight particle size distributions over both types of supports. SEA synthesis of well dispersed nanoparticles results in higher activity than commercial Ru catalysts with higher Ru loadings. The dramatic, beneficial effect of potassium doping is reported for the first time. The carbon support yields higher inherent activity than alumina. Activity as a function of particle size appears to go through a maximum at about 1.5 nm for both supports and suggests hydrogenation of LA is structure sensitive on Ru particle size. Catalyst deactivation after 24 h occurs to significant extents (8 – 58%) mainly by nanoparticle sintering, but also by minor amounts of K loss in K-doped samples. Secondly, a systematic study with alkali and alkaline earth elements was carried out to verify the origin of the promotion effect and the optimal ratio of dopant to Ru. Series of catalysts were prepared by impregnating various amounts of alkali onto 2% Ru/alumina (itself synthesized with high Ru dispersion by strong electrostatic adsorption) and were evaluated for LA hydrogenation. With the ratio of dopant to Ru constant, strong promotional effects of alkali and alkaline earth metals on the activity in terms of turnover frequency (TOF) were observed in the following order Na+ Furthermore, we report the rational synthesis of bimetallic RuRe catalysts supported on VXC-72R carbon and γ-Al2O3 comparing co-strong electrostatic adsorption (co-SEA) to a more traditional method, co-dry impregnation (co-DI). We have found that the bimetallic catalyst exhibits an optimum activity with a Ru:Re atomic ratio of 2:1. In order to establish a correlation between catalytic properties and structure, selected catalysts were characterized by TPR-H2, XRD, STEM/EDXS elemental mapping, XPS and CO-FTIR. The formation of a RuRe alloy along with segregated ReOx particles suggests that the geometric effect on activity promotion is more significant. XRD data of post reaction bimetallic catalysts indicate particle sintering and separated two metal particles for catalysts prepared by co-DI, but not for catalysts prepared by co-SEA

Testing the phenomenological interacting dark energy with observational H(z)H(z) data

In order to test the possible interaction between dark energy and dark matter, we investigate observational constraints on a phenomenological scenario, in which the ratio between the dark energy and matter densities is proportional to the power law case of the scale factor, $r\equiv (\rho_X/\rho_m)\propto a^{\xi}$. By using the Markov chain Monte Carlo method, we constrain the phenomenological interacting dark energy model with the newly revised $H(z)$ data, as well as the cosmic microwave background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) results, the baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample and the type Ia supernovae (SNe Ia) from Union2 set. The best-fit values of the model parameters are $\Omega_{m0}=0.27_{-0.02}^{+0.02}(1\sigma)_{-0.03}^{+0.04}(2\sigma)$, $\xi=3.15_{-0.50}^{+0.48}(1\sigma)_{-0.71}^{+0.72}(2\sigma)$, and $w_X=-1.05_{-0.14}^{+0.15}(1\sigma)_{-0.21}^{+0.21}(2\sigma)$, which are more stringent than previous results. These results show that the standard $\Lambda$CDM model without any interaction remains a good fit to the recent observational data; however, the interaction that the energy transferring from dark matter to dark energy is slightly favored over the interaction from dark energy to dark matter. It is also shown that the $H(z)$ data can give more stringent constraints on the phenomenological interacting scenario when combined to CMB and BAO observations, and the confidence regions of $H(z)$+BAO+CMB, SNe+BAO+CMB, and $H(z)$+SNe+BAO+CMB combinations are consistent with each other.Comment: 6 pages, 4 figures, 1 table. MNRAS in pres

Effect of surfactants on the pretreatment of sugarcane bagasse with dilute ammonia

Lignocellulosic biomass is composed of cellulose, hemicellulose and lignin which are not readily available for conversion in their native form. It is widely accepted that lignin acts as the “glue” that binds cellulose and hemicellulose, giving rigidity and resistance to lignocellulose. The use of non-ionic surfactants during pretreatment can help alter the structure of lignocellulosic biomass to improve cellulose digestibility and ethanol yields. Tween 80, Tween 20, PEG 4000, or PEG 6000 was used with ammonium hydroxide for the pretreatment of sugarcane bagasse. The pretreatment was carried out by mixing sugarcane bagasse, ammonium hydroxide (28% v/v) and water at a ratio of 1: 0.5: 20, adding 3% (w/w) surfactant based on the weight of dry biomass, and heating the mixture to 160 °C for 1 h. The final concentration of ammonium hydroxide was 0.65% w/w at 4.7% solids loading. Chemical compositions were determined before and after pretreatment. Fibers were hydrolyzed using commercial enzymes, Spezyme CP and Novozyme 188. Fermentable sugars and ethanol concentrations were analyzed by HPLC. The results indicated that PEG 4000 and Tween 80 gave the highest cellulose digestibilities (62%, 66%) and ethanol yields (73%, 69 %), respectively. Tween 80 was selected over PEG 4000 because of its low cost. The effect of two concentrations of ammonium hydroxide 0.26% w/w (1: 0.2: 20, biomass: ammonium hydroxide: water ratio) and 0.65% w/w (1: 0.5: 20, biomass: ammonium hydroxide: water ratio), and Tween 80 (1.5%, 3% and 5% w/w, based on the weight of dry biomass) were evaluated during pretreatment at 4.7% solids loading. The greatest lignin removal (37%), cellulose digestibility (66%) and hemicellulose digestibility (43%) were observed at 1: 0.5: 20 ratio supplemented with 3% (w/w) Tween 80. These pretreatment parameters were selected for scale-up experiments at a higher solids loading (10.5%) in a 20 L bioreactor. The greatest lignin removal (55%), cellulose digestibility (72%) and hemicellulose digestibility (57%) were observed with 3% Tween 80-dilute ammonia pretreatment at 1: 0.5: 8 ratio with a final concentration of ammonium hydroxide of 1.47% w/w. Morphological changes in the structure of non-ionic surfactant-dilute ammonia pretreated sugarcane bagasse were observed