Contamination of stellar-kinematic samples and uncertainty about dark matter annihilation profiles in ultrafaint dwarf galaxies: the example of Segue I

The expected gamma-ray flux coming from dark matter annihilation in dwarf spheroidal (dSph) galaxies depends on the so-called `J-factor', the integral of the squared dark matter density along the line-of-sight. We examine the degree to which estimates of J are sensitive to contamination (by foreground Milky Way stars and stellar streams) of the stellar-kinematic samples that are used to infer dark matter densities in `ultrafaint' dSphs. Applying standard kinematic analyses to hundreds of mock data sets that include varying levels of contamination, we find that mis-classified contaminants can cause J-factors to be overestimated by orders of magnitude. Stellar-kinematic data sets for which we obtain such biased estimates tend 1) to include relatively large fractions of stars with ambiguous membership status, and 2) to give estimates for J that are sensitive to specific choices about how to weight and/or to exclude stars with ambiguous status. Comparing publicly-available stellar-kinematic samples for the nearby dSphs Reticulum~II and Segue~I, we find that only the latter displays both of these characteristics. Estimates of Segue~I's J-factor should therefore be regarded with a larger degree of caution when planning and interpreting gamma-ray observations. Moreover, robust interpretations regarding dark matter annihilation in dSph galaxies in general will require explicit examination of how interlopers might affect the inferred dark matter density profile.Comment: 12 pages, 8 figures. New appendix A (joint light/dark matter likelihood), results unchanged. Match accepted MNRAS versio

Spherical Jeans analysis for dark matter indirect detection in dwarf spheroidal galaxies - Impact of physical parameters and triaxiality

Dwarf spheroidal (dSph) galaxies are among the most promising targets for the indirect detection of dark matter (DM) from annihilation and/or decay products. Empirical estimates of their DM content - and hence the magnitudes of expected signals - rely on inferences from stellar-kinematic data. However, various kinematic analyses can give different results and it is not obvious which are most reliable. Using extensive sets of mock data of various sizes (mimicking 'ultra-faint' and 'classical' dSphs) and an MCMC engine, here we investigate biases, uncertainties, and limitations of analyses based on parametric solutions to the spherical Jeans equation. For a variety of functional forms for the tracer and DM density profiles, as well as the orbital anisotropy profile, we examine reliability of estimates for the astrophysical J- and D-factors for annihilation and decay, respectively. For large (N > 1000) stellar-kinematic samples typical of 'classical' dSphs, errors tend to be dominated by systematics, which can be reduced through the use of sufficiently general and flexible functional forms. For small (N < 100) samples typical of 'ultrafaints', statistical uncertainties tend to dominate systematic errors and flexible models are less necessary. We define an optimal strategy that would mitigate sensitivity to priors and other aspects of analyses based on the spherical Jeans equation. We also find that the assumption of spherical symmetry can bias estimates of J (with the 95% credibility intervals not encompassing the true J-factor) when the object is mildly triaxial (axis ratios b/a = 0.8, c/a = 0.6). A concluding table summarises the typical error budget and biases for the different sample sizes considered.Comment: 21 pages, 20 figures. Minor changes (several clarifications): match the MNRAS accepted versio

A Supersymmetric Flipped SU(5) Intersecting Brane World

We construct an N=1 supersymmetric three-family flipped SU(5) model from type IIA orientifolds on $T^6/(\Z_2\times \Z_2)$ with D6-branes intersecting at general angles. The spectrum contains a complete grand unified and electroweak Higgs sector. In addition, it contains extra exotic matter both in bi-fundamental and vector-like representations as well as two copies of matter in the symmetric representation of SU(5).Comment: 17 pages, 3 tables, v2 published in Phys.Lett.

Stress versus temperature dependent activation energies in creep

The activation energy for creep at low stresses and elevated temperatures is lattice diffusion, where the rate controlling mechanism for deformation is dislocation climb. At higher stresses and intermediate temperatures, the rate controlling mechanism changes from that of dislocation climb to one of obstacle-controlled dislocation glide. Along with this change, there occurs a change in the activation energy. It is shown that a temperature-dependent Gibbs free energy does a good job of correlating steady-state creep data, while a stress-dependent Gibbs free energy does a less desirable job of correlating the same data. Applications are made to copper and a LiF-22 mol. percent CaF2 hypereutectic salt

Information communication technology (ICT) implementation constraints: a construction industry perspective

PURPOSE - The purpose of this paper is to report upon research undertaken on deployment of information communication technology (ICT) diffusion initiatives in the Australian construction industry. The paper seeks to explain how innovation implementation drivers and barriers facilitate diffusion at the organisational, group and individual levels. DESIGN/METHODOLOGY/APPROACH - Data from two web-based document management case studies and one intranet document management system case study are used to analyse ICT diffusion dynamics within three large information technology (IT) literate Australian construction firms. The sample was purposefully limited to large IT-literate construction contracting organisations with a need to use ICT for their operational effectiveness. FINDINGS - Constraints at the personal level include limited budget for ICT investment, commitment from other project participants, issues of ICT standardisation, and security problems. At the organisational level, constraints include basic levels computer experience, time available to learn, and the identification of clear benefits of ICT use. Constraints at the group level include time available to share information, quality of personal contact and geographical distance. RESEARCH LIMITATIONS/IMPLICATIONS - The sample was purposefully limited to large IT-literate construction contracting organisations with a need to use ICT for their operational effectiveness. PRACTICAL IMPLICATIONS - The driver and barrier models presented indicate that ICT innovation implementation requires intense management interventions to facilitate a supportive workplace environment that strongly links personal and organisational resource investment with demonstrated outcome benefits. ORIGINALITY/VALUE - This study provides rich insights of the dynamics of ICT innovation implementation. Few studies in the literature have provided such insights that link the organisational, group and individual levels

Innovation diffusion at the implementation stage of a construction project: case study of information communication technology

Interest in construction industry (CI) innovation, particularly in information communication technology (ICT), has been steadily growing with the advent and widespread use of the Internet. However, despite its potential for delivering competitive advantage, many companies have failed to effectively realize promised benefits from ICT due to misunderstanding the relationship between factors and processes influencing ICT implementation. Results from recent in-depth qualitative ICT implementation research on three construction contractors provides useful insights and practical experience of lessons learned that can be more broadly disseminated. These research results provide an ICT innovation diffusion organizational level framework with insights about how it may be applied to improve ICT adoption at different implementation stages for the CI. They suggest that strategic ICT implementation planning needs to consider issues of critical management support, technical support, supportive workplace environment and ICT users&#039; individual-characteristics so that the framework processes offered can be effectively applied

Astrometric jitter of the sun as a star

The daily variation of the solar photocenter over some 11 years is derived from the Mount Wilson data reprocessed by Ulrich et al. 2010 to closely match the surface distribution of solar irradiance. The standard deviations of astrometric jitter are 0.52 $\mu$AU and 0.39 $\mu$AU in the equatorial and the axial dimensions, respectively. The overall dispersion is strongly correlated with the solar cycle, reaching $0.91 \mu$AU at the maximum activity in 2000. The largest short-term deviations from the running average (up to 2.6 $\mu$AU) occur when a group of large spots happen to lie on one side with respect to the center of the disk. The amplitude spectrum of the photocenter variations never exceeds 0.033 $\mu$AU for the range of periods 0.6--1.4 yr, corresponding to the orbital periods of planets in the habitable zone. Astrometric detection of Earth-like planets around stars as quiet as the Sun is not affected by star spot noise, but the prospects for more active stars may be limited to giant planets.Comment: Accepted in Ap

Symmetry of the order parameter in superconducting ZrZn_2

We apply symmetry considerations to study the possible superconducting order parameters in ferromagnetic ZrZn_2. We predict that the presence and the location of the superconducting gap nodes depend on the direction of magnetization M. In particular, if M is directed along the z axis, then the order parameter should always have zeros. We also discuss how to determine the gap symmetry in ZrZn_2 using ultrasound attenuation measurements.Comment: 6 pages, submitted to PRB; some corrections and discussion adde