University of Massachusetts Amherst

About: University of Massachusetts Amherst is a education organization based out in Amherst Center, Massachusetts, United States. It is known for research contribution in the topics: Population & Galaxy. The organization has 37274 authors who have published 83965 publications receiving 3834996 citations. The organization is also known as: UMass Amherst & Massachusetts State College.

The redshift dependence of the structure of massive Λ cold dark matter haloes

Abstract: We use two very large cosmological simulations to study how the density profiles of relaxedCDM dark halos depend on redshift and on halo mass. We confirm that these profiles deviate slightly but systematically from the NFW form and are better approximated by the empirical formula, dlog ρ/dlog r ∝ r � , first used by Einasto to fit star counts in the Milky Way. The best-fit value of the additional shape parameter, α, increases gradually with mass, from α ∼ 0.16 for present-day galaxy halos to α ∼ 0.3 for the rarest and most massive clusters. Halo concentrations depend only weakly on mass at z = 0, and this dependence weakens further at earlier times. At z ∼ 3 the average concentration of relaxed halos does not vary appreciably over the mass range accessible to our simulations (M ∼3×10 11 h −1 M⊙). Furthermore, in our biggest simulation, the average concentration of the most massive, relaxed halos is constant at h c200i ∼ 3.5 to 4 for 0 ≤ z ≤ 3. These results agree well with those of Zhao et al (2003b) and support the idea that halo densities reflect the density of the universe at the time they formed, as proposed by Navarro, Frenk & White (1997). With their original parameters, the NFW prescription overpredicts halo concentrations at high redshift. This shortcoming can be reduced by modifying the definition of halo formation time, although the evolution of the concentrations of Milky Way mass halos is still not reproduced well. In contrast, the much-used revisions of the NFW prescription by Bullock et al. (2001) and Eke, Navarro & Steinmetz (2001) predict a steeper drop in concentration at the highest masses and stronger evolution with redshift than are compatible with our numerical data. Modifying the parameters of these models can reduce the discrepancy at high masses, but the overly rapid redshift evolution remains. These results have important implications for currently planned surveys of distant clusters.

How to Transform Consumers into Fans of Your Brand

Abstract: Purpose – Brand fan pages on social networks have become very popular online services. However, empirical research on fan pages is still in its infancy. Therefore, the purpose of this study is to investigate the effect of fan pages on the customer-brand relationship and what motivates users to participate.Design/methodology/approach – For this a framework was developed based on classical concepts of use and gratification theory, customer engagement, and involvement theory. The model is tested using a multi-step approach of qualitative and quantitative methods.Findings – The paper can show a significant influence from online service usage behavior on the fan page on the customer-brand relationship. Furthermore, the paper identifies different values such as functional and hedonic content as drivers of fan-page participation.Research limitations/implications – The results are limited by the used data set, which is not representative for all industries and is cross-sectional. Further research could build up a database over a longitudinal time frame in different industries. The results are interesting for theory and practice. They confirm the positive effect of integration and engagement in general and show that fan pages are more than just tools to connect brand fans. They are also instruments for gaining new fans. Originality/value – The present study is the first study that not only shows the effect of fan pages on customer behavior, but also analyses the motives for participation and the crucial constructs to manage them successfully.

Large-scale structure of the molecular gas in Taurus revealed by high linear dynamic range spectral line mapping

Abstract: We report the results of a 100 deg2 survey of the Taurus molecular cloud region in 12CO and 13CO -->J = 1→ 0. The image of the cloud in each velocity channel includes -->3 × 106 Nyquist-sampled pixels on a 20 -->'' grid. The high sensitivity and large spatial dynamic range of the maps reveal a very complex, highly structured cloud morphology, including filaments, cavities, and rings. The axes of the striations seen in the 12CO emission from relatively diffuse gas are aligned with the direction of the magnetic field. We have developed a statistical method for analyzing the pixels in which 12CO but not 13CO is detected, which allows us to determine the CO column in the diffuse portion of the cloud, as well as in the denser regions in which we detect both isotopologues. Using a column-density-dependent model for the CO fractional abundance, we derive the mass of the region mapped to be -->2.4 × 104 M☉, more than twice as large as would be obtained using a canonical fixed fractional abundance of 13CO, and a factor of 3 greater than would be obtained considering only the high column density regions. We determine that half the mass of the cloud is in regions having column density below -->2.1 × 1021 cm−2. The distribution of young stars in the region covered is highly nonuniform, with the probability of finding a star in a pixel with a specified column density rising sharply for -->N(H2) = 6 × 1021 cm−2. We determine a relatively low star formation efficiency (mass of young stars/mass of molecular gas), between 0.3% and 1.2%, and an average star formation rate during the past 3 Myr of -->8 × 10−5 stars yr−1.

Electron performance measurements with the ATLAS detector using the 2010 LHC proton-proton collision data

Abstract: Detailed measurements of the electron performance of the ATLAS detector at the LHC are reported, using decays of the Z, W and J/psi particles. Data collected in 2010 at root s = 7 TeV are used, corresponding to an integrated luminosity of almost 40 pb(-1). The inter-alignment of the inner detector and the electromagnetic calorimeter, the determination of the electron energy scale and resolution, and the performance in terms of response uniformity and linearity are discussed. The electron identification, reconstruction and trigger efficiencies, as well as the charge misidentification probability, are also presented.