Peculiar velocity measurement in a clumpy universe

In this work we address the issue of peculiar velocity measurement in a perturbed Friedmann universe using the deviations from measured luminosity distances of standard candles from background FRW universe. We want to show and quantify the statement that in intermediate redshifts ($0.5< z < 2$), deviations from the background FRW model are not uniquely governed by peculiar velocities. Luminosity distances are modified by gravitational lensing. We also want to indicate the importance of relativistic calculations for peculiar velocity measurement at all redshifts. For this task we discuss the relativistic correction on luminosity distance and redshift measurement and show the contribution of each of the corrections as lensing term, peculiar velocity of the source and Sachs-Wolfe effect. Then we use the SNe Ia sample of Union 2, to investigate the relativistic effects we consider. We show that, using the conventional peculiar velocity method, that ignores the lensing effect, will result in an overestimate of the measured peculiar velocities at intermediate redshifts. Here we quantify this effect. We show that at low redshifts the lensing effect is negligible compare to the effect of peculiar velocity. From the observational point of view, we show that the uncertainties on luminosity of the present SNe Ia data prevent us from precise measuring the peculiar velocities even at low redshifts ($z<0.2$).Comment: 15 pages, 5 figures, Int. J. Mod. Phys. D 27, 1850019 (2018

The challenge of large and empty voids in the SDSS DR7 redshift survey

We present catalogues of voids for the SDSS DR7 redshift survey and for Millennium I simulation mock data. We aim to compare the observations with simulations based on a $\Lambda$CDM model and a semi-analytic galaxy formation model. We use the void statistics as a test for these models. We assembled a mock catalogue that closely resembles the SDSS DR7 catalogue and carried out a parallel statistical analysis of the observed and simulated catalogue. We find that in the observation and the simulation, voids tend to be equally spherical. The total volume occupied by the voids and their total number are slightly larger in the simulation than in the observation. We find that large voids are less abundant in the simulation and the total luminosity of the galaxies contained in a void with a given radius is higher on average than observed by SDSS DR7 survey. We expect these discrepancies to be even more significant in reality than found here since the present value of $\sigma_8$ given by WMAP7 is lower than the value of 0.9 used in the Millennium I simulation. The reason why the simulation fails to produce enough large and dark voids might be the failure of certain semi-analytic galaxy formation models to reduce the small-scale power of $\Lambda$CDM and to produce sufficient power on large scales.Comment: Kolmogrov-Smirnov test added. version to appear in A&

Surface modification of colloidal semiconductor nanocrystal quantum dots

Current quantum dot surface modification strategies rely heavily on ligand exchange that removes the nanocrystal\u27s native ligands originated from its synthesis. This can cause etching and introduce surface defects, affecting the nanocrystal\u27s optical properties. In addition, common ligand exchange method fails to control the degree of functionalization or the number of functional groups introduced per nanocrystal. We describe our work on surface modification of semiconductor nanocrystal quantum dots investigating a new approach that not only bypasses ligand exchange and introduces native active ligands with original optical properties, but also is able to control the degree of surface loading, called valence , in semiconductor nanocrystal quantum dots. We show that surface doped quantum dots capped with chemically-active native ligands can be prepared directly from a mixture of ligands with similar chain lengths. Initial ratio between chemically active and inactive ligands is retained on the nanocrystal surface, allowing to control the extent of surface modification. The extent of surface coverage by a particular functional group will have a large impact on a nanocrystal affinity and permeability to a variety of biological structures. It also affects nanocrystal\u27s ability to localize, penetrate, and transport across specific tissues, cellular and subcellular structures. We show that we are able to control the loading of cholestanone per quantum dot nanocrystal. We observed that samples with higher steroid loading infuse themselves more with the lipid membrane compare to those with no or little steroid. To further investigate the surface ligand packing, structure and reactivity, we apply advanced solution NMR techniques to determine surface ligand organization and chemistry. Two-dimension ROESY studies show that ligands with the same chain length tend to homogeneously distribute themselves onto the nanocrystal\u27s surface however ligands with the different chain length tend to form islands. Furthermore, we demonstrate that surface ligand organization can affect the reactivity of quantum dots. Formation of rafts as a result of packing ligands of a same length, increase the local concentration of reactive terminal group and facilitate the chemical reactivity at the surface of quantum dots. We also synthesize multifunctional multidentate polymeric ligand via ADMET. Varying the total dienes-to-Ru catalyst ratio allows us to control the extent of ADMET, which enables us to achieve an accurate control over polydentate ligand size. We use the synthetic polymer as a linkage for constructing gold-QD heterostructure. We hope that this study can provide a new avenue to understand the organic/inorganic boundary of other and more complex nanoparticle/ligand systems

Distribution and Fate of Per- and Polyfluorinated Alkyl Substances (PFAS) in Wastewater Treatment Plants Discharging to Great Bay

Per-and polyfluoroalkyl substances (PFAS) represent a major class of emerging contaminants composed of nearly 5000 human-made chemicals. PFAS have been used since the 1950s as surfactants in industrial and consumer products due to their unique water and oil repellency, high surface activity, and thermostability. These compounds can bioaccumulate and pose human and ecological health concerns; for example, PFAS intensive exposure can affect the liver, reproduction and development in humans and wildlife. Ubiquitous presence of these compounds in different environmental matrices, high persistency, and potential threats to human and environmental health, have made it critical to develop an understanding of how they are distributed in different matrices and how people get exposed. Previous studies have provided some understanding of how environmental conditions, chemical structures and properties affect PFAS distribution, fate, and their biotransformation. In addition, PFAS environmental exposure studies have been completed or are underway; and while it is clear that exposures are occurring, the effects associated with exposure are not fully understood and therefore there is significant uncertainty associated with evaluation of risks associated with PFAS in environment. Wastewater treatment facilities (WWTFs) are a conduit of PFAS which are not originally designed for the removal of these low level and diverse contaminants. In this study, PFAS distribution and fate in six WWTFs discharging their effluent into Great Bay Estuary in March and July 2019 were investigated. PFAS were detected in influent and effluent of WWTFs with up to 12 detected constituents out of 24 measured by standard analytical method (LC/MS/MS). In general, PFAS concentrations increased in effluent after biological treatment which supports the presence of unknown PFAS precursors in influent not measured during standard analytical method. Seasonal changes exhibited a significant influence on PFAS concentrations in effluent. Higher PFAS concentrations were detected in the warmer season, indicating the effect of temperature and higher microbial activities on PFAS precursor degradation. In addition, PFAS precursors were indirectly quantified by oxidizing precursors into terminal PFAAs compounds using the total oxidizable precursor assay (TOP assay). Higher perfluoroalkyl acids (PFAA) concentrations after oxidation compared to unoxidized samples confirmed the presence of PFAS precursors in WWTFs

Globoid Cell Leukodystrophy (Krabbe Disease)

How to Cite This Article: TAvasoli A. Globoid Cell Leukodystrophy (Krabbe Disease). Iran J Child Neurol. Autumn 2014;8;4(Suppl.1):14-15.pls see pdf

Unraveling the nature of Gravity through our clumpy Universe

We propose a new probe to test the nature of gravity at various redshifts through large-scale cosmological observations. We use our void catalog, extracted from the Sloan Digital Sky Survey (SDSS, DR10), to trace the distribution of matter along the lines of sight to SNe Ia that are selected from the Union 2 catalog. We study the relation between SNe Ia luminosities and convergence and also the peculiar velocities of the sources. We show that the effects, on SNe Ia luminosities, of convergence and of peculiar velocities predicted by the theory of general relativity and theories of modified gravities are different and hence provide a new probe of gravity at various redshifts. We show that the present sparse large-scale data does not allow us to determine any statistically- significant deviation from the theory of general relativity but future more comprehensive surveys should provide us with means for such an exploration.Comment: Essay received honorable mention in the Gravity Research Foundation 2014 essay competition. To appear in IJMPD. 10 pages, 2 figure

A statistical study of the luminosity gap in galaxy groups

The luminosity gap between the two brightest members of galaxy groups and clusters is thought to offer a strong test for the models of galaxy formation and evolution. This study focuses on the statistics of the luminosity gap in galaxy groups, in particular fossil groups, e.g. large luminosity gap, in an analogy with the same in a cosmological simulation. We use spectroscopic legacy data of seventh data release (DR7) of SDSS, to extract a volume limited sample of galaxy groups utilizing modified friends-of-friends (mFoF) algorithm. Attention is paid to galaxy groups with the brightest group galaxy (BGG) more luminous than \Mr = -22. An initial sample of 620 groups in which 109 optical fossil groups, where the luminosity gap exceeds 2 magnitude, were identified. We compare the statistics of the luminosity gap in galaxy groups at low mass range from the SDSS with the same in the Millennium simulations where galaxies are modeled semi-analytically. We show that the BGGs residing in galaxy groups with large luminosity gap, i.e. fossil groups, are on average brighter and live in lower mass halos with respect to their counter parts in non-fossil systems. Although low mass galaxy groups are thought to have recently formed, we show that in galaxy groups with 15 galaxies brighter than $M_r\ge -19.5$, evolutionary process are most likely to be responsible for the large luminosity gap. We also examine a new probe of finding fossil group. In addition we extend the recently introduced observational probe based on the luminosity gap, the butterfly diagram, to galaxy groups and study the probe as a function of halo mass. This probe can, in conjunction with the luminosity function, help to fine tune the semi-analytic models of galaxies employed in the cosmological simulations.Comment: 11 pages, 11 figures, accepted to PASP journa