Mad2, Bub3, and Mps1 regulate chromosome segregation and mitotic synchrony in Giardia intestinalis, a binucleate protist lacking an anaphase-promoting complex.

The binucleate pathogen Giardia intestinalis is a highly divergent eukaryote with a semiopen mitosis, lacking an anaphase-promoting complex/cyclosome (APC/C) and many of the mitotic checkpoint complex (MCC) proteins. However, Giardia has some MCC components (Bub3, Mad2, and Mps1) and proteins from the cohesin system (Smc1 and Smc3). Mad2 localizes to the cytoplasm, but Bub3 and Mps1 are either located on chromosomes or in the cytoplasm, depending on the cell cycle stage. Depletion of Bub3, Mad2, or Mps1 resulted in a lowered mitotic index, errors in chromosome segregation (including lagging chromosomes), and abnormalities in spindle morphology. During interphase, MCC knockdown cells have an abnormal number of nuclei, either one nucleus usually on the left-hand side of the cell or two nuclei with one mislocalized. These results suggest that the minimal set of MCC proteins in Giardia play a major role in regulating many aspects of mitosis, including chromosome segregation, coordination of mitosis between the two nuclei, and subsequent nuclear positioning. The critical importance of MCC proteins in an organism that lacks their canonical target, the APC/C, suggests a broader role for these proteins and hints at new pathways to be discovered

Beam squint and Stokes V with off-axis feeds

Radio telescopes with off-axis feeds, such as the (E)VLA, suffer from "beam squint" in which the two orthogonal circular polarizations sampled have different pointing centers on the sky. Its effects are weak near the beam center but become increasingly important towards the edge of the antenna power pattern where gains in the two polarizations at a given sky position are significantly different. This effect has limited VLA measurements of circular polarization (Stokes V) and introduced dynamic range limiting, wide-field artifacts in images made in Stokes I. We present an adaptation of the visibility-based deconvolution CLEAN method that can correct this defect "on the fly" while imaging, correcting as well the associated self-calibration. We present two examples of this technique using the procedure "Squint" within the Obit package which allows wide-field imaging in Stokes V and reduced artifacts in Stokes I. We discuss the residual errors in these examples as well as a scheme for future correction of some of these errors. This technique can be generalized to implement temporally- and spatially-variable corrections, such as pointing and cross-polarization leakage errors.Comment: 9 pages, 6 figures (five of them double), to appear in Astronomy & Astrophysics (accepted: May 9, 2008). High-resolution versions of the figures (gzipped, tar,gzipped) can be downloaded from http://www.cv.nrao.edu/~juson/technical/squint/squint_figures.g

Dynamic and Structure of the Italian stock market based on returns and volume trading

In this paper we introduce a new method to describe dynamical patterns of multidimensional time. The method combines the tools of Symbolic Time Series Analysis with the nearest neighbor single linkage clustering algorithm. Data symbolization allows to obtain a metric distance between two different time series that is used to construct an ultrametric distance. The methodology is applied to examine the dynamics and structure of the Italian stock market considering both asset returns and volume trading to model the market. We derive a hierarchical organization, constructing minimal-spanning and hierarchical trees, both in normal and extreme situations of the market. From these trees we detect four clusters of firms according to their proximity. We show that the financial cluster is in a central position of the minimal spanning tree, both in normal and extreme situations, reflecting that financial companies represent more than 30% of the Italian market capitalization. We also show that the derived clusters corresponds with companies sharing common economic activities.

Heating of Flare Loops With Observationally Constrained Heating Functions

We analyze high cadence high resolution observations of a C3.2 flare obtained by AIA/SDO on August 1, 2010. The flare is a long duration event with soft X-ray and EUV radiation lasting for over four hours. Analysis suggests that magnetic reconnection and formation of new loops continue for more than two hours. Furthermore, the UV 1600\AA\ observations show that each of the individual pixels at the feet of flare loops is brightened instantaneously with a timescale of a few minutes, and decays over a much longer timescale of more than 30 minutes. We use these spatially resolved UV light curves during the rise phase to construct empirical heating functions for individual flare loops, and model heating of coronal plasmas in these loops. The total coronal radiation of these flare loops are compared with soft X-ray and EUV radiation fluxes measured by GOES and AIA. This study presents a method to observationally infer heating functions in numerous flare loops that are formed and heated sequentially by reconnection throughout the flare, and provides a very useful constraint to coronal heating models.Comment: This paper is revise

Applying the Open Source Development Model to Knowledge Work

This paper introduces a distinction between two different types of information goods in order to analyse the processes governing the review and integration of multi-authored contributions to information goods such as those produced through collaborations using the Internet as well as modular information goods such as open source software. It is argued that these distinctions are important because they suggest different organisational arrangements for producing such information goods. This method of analysing the nature of the information goods is employed to examine different organisational arrangements using the analogy of collaboration for traditional publication to identify actors and processes. The analysis of 'contributors' is extended from authorship to collectors and researchers. The paper examines a small survey of the governance procedures employed in projects that employ open source methods for collecting various types of information. We noted the prime role of the recruitment process in the relative success of the examples that we examined (ODP, Wikipedia, Nupedia, MathLearning, VRoma, and Web of Life). For these 'collection' efforts, the role of hierarchy in editing and review of project submissions appears to be important than in open source communities and may be an impediment to recruitment and project development. A number of directions for further research are identified.open source software, collaboration, hierarchies, trust, teams, co-operation

A DFT + U study on structural, electronic, vibrational and thermodynamic properties of TiO 2 polymorphs and hydrogen titanate: tuning the Hubbard ‘ U -term’

Structural, electronic, vibrational and thermodynamic properties have been tested when Hubbard parameter U is implemented in density functional theory calculations for TiO2 polymorphs: anatase, rutile, TiO2?B and for hydrogen titanate (H2Ti3O7) bulk. Optimum U parameter values were found for each system, balancing geometric changes and electronic properties, namely, U = 4 eV for anatase and TiO2?B, U = 5 eV for rutile and hydrogen titanate. Although the addition of this parameter improves the prediction of electronic properties, with no significant structural changes, we found that it would not be adequate for predicting vibrational properties.Fil: German, Estefania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina. Universidad de la República; UruguayFil: Faccio Sgiorovello, Ricardo Juan. Universidad de la República; UruguayFil: Mombrú, Alvaro W. Universidad de la República; Urugua

The Open Source Way of Working: a New Paradigm for the Division of Labour in Software Development?

The interest the Open Source Software Development Model has recently raised amongst social scientists has resulted in an accumulation of relevant research concerned with explaining and describing the motivations of Open Source developers and the advantages the Open Source methodology has over traditional proprietary software development models. However, existing literature has often examined the Open Source phenomenon from an excessively abstract and idealised perspective of the common interests of open source developers, therefore neglecting the very important organisational and institutional aspects of communities of individuals that may, in fact, have diverse interests and motivations. It is the aim of this paper to begin remedying this shortcoming by analysing the sources of authority in Open Source projects and the hierarchical structures according to which this authority is organised and distributed inside them. In order to do so, a theoretical framework based on empirical evidence extracted from a variety of projects is built, its main concerns being the description and explanation of recruitment, enculturation, promotion and conflict resolution dynamics present in Open Source projects. The paper argues that 'distributed authority' is a principal means employed by such communities to increase stability, diminish the severity and scope of conflicts over technical direction, and ease the problems of assessing the quality of contributions. The paper also argues that distributed authority is principally derived from interpersonal interaction and the construction of trust between individuals drawn to the project by diverse interests that are mediated and moderated through participants' common interest in the project's successful outcome. The paper presents several conclusions concerning the governance of open source communities and priorities for future research.open source software, hierarchies, trust, teams, co-operation.