University of California, Santa Cruz

About: University of California, Santa Cruz is a education organization based out in Santa Cruz, California, United States. It is known for research contribution in the topics: Galaxy & Population. The organization has 15541 authors who have published 44120 publications receiving 2759983 citations. The organization is also known as: UCSC & UC, Santa Cruz.

Hidden Markov models for sequence analysis: extension and analysis of the basic method

Abstract: Hidden Markov models (HMMs) are a highly effective means of modeling a family of unaligned sequences or a common motif within a set of unaligned sequences. The trained HMM can then be used for discrimination or multiple alignment. The basic mathematical description of an HMM and its expectation-maximization training procedure is relatively straightforward. In this paper, we review the mathematical extensions and heuristics that move the method from the theoretical to the practical. We then experimentally analyze the effectiveness of model regularization, dynamic model modification and optimization strategies. Finally it is demonstrated on the SH2 domain how a domain can be found from unaligned sequences using a special model type. The experimental work was completed with the aid of the Sequence Alignment and Modeling software suite.

Star Formation in AEGIS Field Galaxies since z = 1.1: Staged Galaxy Formation and a Model of Mass-dependent Gas Exhaustion

Abstract: We analyze star formation (SF) as a function of stellar mass (M☉) and redshift z in the All-Wavelength Extended Groth Strip International Survey, for star-forming field galaxies with M* ≳ 10^10 M☉ out to z = 1.1. The data indicate that the high specific SF rates (SFRs) of many less massive galaxies do not represent late, irregular or recurrent, starbursts in evolved galaxies. They rather seem to reflect the onset (initial burst) of the dominant SF episode of galaxies, after which SF gradually declines on gigayear timescales to z = 0 and forms the bulk of a galaxy’s M*. With decreasing mass, this onset of major SF shifts to decreasing z for an increasing fraction of galaxies (staged galaxy formation). This process may be an important component of the “downsizing” phenomenon. We find that the predominantly gradual decline of SFRs described by Noeske et al. can be reproduced by exponential SF histories (τ models), if less massive galaxies have systematically longer e-folding times τ, and a later onset of SF (zf). Our model can provide a first parameterization of SFR as a function of M* and z, and quantify mass dependences of τ and z, from direct observations of M* and SFRs up to z > 1. The observed evolution of SF in galaxies can plausibly reflect the dominance of gradual gas exhaustion. The data are also consistent with the history of cosmological accretion onto dark matter halos.

Dialogue in the Classroom.

Abstract: There is increasing agreement among those who study classrooms that learning is likely to be most effective when students are actively involved in the dialogic coconstruction of meaning about topics that are of significance to them. This article reports the results of an extended collaborative action research project in which teachers attempted to create the conditions for such dialogue by adopting an inquiry approach to the curriculum. A quantitative comparison between observations made early and late in the teachers' involvement in the project showed a number of significant changes in the characteristics of teacher–whole-class discourse, with a shift toward a more dialogic mode of interaction. Nevertheless, the initiation-response-follow-up (IRF) genre continued to be pervasive. Despite this, when the same observations were examined qualitatively, there was clear evidence of an increase over time in the teachers' adoption of a "dialogic stance." The article concludes with a consideration of the relation...

The DEEP Groth Strip Survey. II. Hubble Space Telescope Structural Parameters of Galaxies in the Groth Strip

Abstract: The quantitative morphological classification of distant galaxies is essential to the understanding of the evolution of galaxies over the history of the universe This paper presents Hubble Space Telescope WFPC2 F606W and F814W photometric structural parameters for 7450 galaxies in the Groth Strip These parameters are based on a two-dimensional bulge + disk surface brightness model and were obtained using an automated reduction and analysis pipeline described in detail here A first set of fits was performed separately in each bandpass, and a second set of fits was performed simultaneously on both bandpasses The information produced by these two types of fits can be used to explore different science goals Systematic and random fitting errors in all structural parameters as well as bulge and disk colors are carefully characterized through extensive sets of simulations The results of these simulations are given in catalogs similar to the real science catalogs so that both real and simulated measurements can be sampled according to the same selection criteria to show biases and errors in the science data subset of interest The effects of asymmetric structures on the recovered bulge+disk fitting parameters are also explored through simulations The full multidimensional photometric survey selection function of the Groth Strip is also computed This selection function, coupled to bias maps from simulations, provides a complete and objective reproduction of the observational limits, and these limits can be applied to theoretical predictions from galaxy evolution models for direct comparisons with the data