581 research outputs found
Causes Leading to Poor site Coordination in Building Projects
It is a common practice for the main contractors of Hong Kong
building projects to sublet most of the works to subcontractors.
However, most of the subcontractors complain that they are unable
to perform to their full capacity due to poor coordination of temporary
works and access road to work places etc. Eighteen common
site coordination problems and sixteen essential causes to the problems were identified from literature and advices from experienced industrial practitioners. The causes were grouped into three categories: staffing related causes; technical related causes; and management system related causes. The contribution, frequency of occurrence and aggregated importance of the causes on the quality of main contractorsâ coordination during the construction stage were ranked through a questionnaire survey. Unclear job duties was found to be the most important cause. The results of the survey established that the most important causes were mainly associated with management systems, especially communications, rather than staffing or technical related factors
Essential Causes Of The Critical Site Coordination Problems In Building Projects: A Hong Kong Study
In Hong Kong, main contractors of building projects tend to subcontract most of their work. However, many of the subcontractors complain that they are unable to perform to their full capacity due main contractorsâ poor site coordination of temporary works and interfacing works and plant supports etc. Six critical site coordination problems caused by main contractors that had adversely influence to the performance of subcontractors were identified in previous study. Twelve essential causes to the problems were identified from literatures and previous studies. A questionnaire survey was conducted to establish a model that explain how the essential causes contributed to the occurrence of the critical site coordination problems which subsequently affected the performance of subcontractors. The survey results were validated by neural network analysis. Backward elimination method was adopted to identify the âmost essentialâ causes that enable main contractors to formulate measures to eliminate the critical site coordination problems. The survey findings show that âdesign of the temporary work provided by main contractor cannot meet the requirements requested by the subcontractorsâ is the âmost essentialâ causes of four out of the six critical site coordination problems
A Large Catalog of Accurate Distances to Molecular Clouds from PS1 Photometry
Distance measurements to molecular clouds are important but are often made separately for each cloud of interest, employing very different data and techniques. We present a large, homogeneous catalog of distances to molecular clouds, most of which are of unprecedented accuracy. We determine distances using optical photometry of stars along lines of sight toward these clouds, obtained from PanSTARRS-1. We simultaneously infer the reddenings and distances to these stars, tracking the full probability distribution function using a technique presented in Green et al. We fit these star-by-star measurements using a simple dust screen model to find the distance to each cloud. We thus estimate the distances to almost all of the clouds in the Magnani et al. catalog, as well as many other well-studied clouds, including Orion, Perseus, Taurus, Cepheus, Polaris, California, and Monoceros R2, avoiding only the inner Galaxy. Typical statistical uncertainties in the distances are 5%, though the systematic uncertainty stemming from the quality of our stellar models is about 10%. The resulting catalog is the largest catalog of accurate, directly measured distances to molecular clouds. Our distance estimates are generally consistent with available distance estimates from the literature, though in some cases the literature estimates are off by a factor of more than two
Pan-STARRS Pixel Analysis: Source Detection and Characterization
Over 3 billion astronomical sources have been detected in the more than 22 million orthogonal transfer CCD images obtained as part of the Pan-STARRS1 3Ï survey. Over 85 billion instances of those sources have been automatically detected and characterized by the Pan-STARRS Image Processing Pipeline photometry software, psphot. This fast, automatic, and reliable software was developed for the Pan-STARRS project but is easily adaptable to images from other telescopes. We describe the analysis of the astronomical sources by psphot in general as well as for the specific case of the third processing version used for the first two public releases of the Pan-STARRS 3Ï Survey data
A Map of Dust Reddening to 4.5 kpc from Pan-STARRS1
We present a map of the dust reddening to 4.5 kpc derived from Pan-STARRS1 stellar photometry. The map covers almost the entire sky north of declination â30° at a resolution of 7'-14', and is based on the estimated distances and reddenings to more than 500 million stars. The technique is designed to map dust in the Galactic plane, where many other techniques are stymied by the presence of multiple dust clouds at different distances along each line of sight. This reddening-based dust map agrees closely with the Schlegel et al. (SFD) far-infrared emission-based dust map away from the Galactic plane, and the most prominent differences between the two maps stem from known limitations of SFD in the plane. We also compare the map with Planck, finding likewise good agreement in general at high latitudes. The use of optical data from Pan-STARRS1 yields reddening uncertainty as low as 25 mmag E(B â V)
Polarization transfer in the HeH reaction
Polarization transfer in the 4He(e,e'p)3H reaction at a Q^2 of 0.4 (GeV/c)^2
was measured at the Mainz Microtron MAMI. The ratio of the transverse to the
longitudinal polarization components of the ejected protons was compared with
the same ratio for elastic ep scattering. The results are consistent with a
recent fully relativistic calculation which includes a predicted medium
modification of the proton form factor based on a quark-meson coupling model.Comment: 5 pages, Latex, 2 postscript figures, submitted to Physics Letters
Hamiltonian Theory of the FQHE: Conserving Approximation for Incompressible Fractions
A microscopic Hamiltonian theory of the FQHE developed by Shankar and the
present author based on the fermionic Chern-Simons approach has recently been
quite successful in calculating gaps and finite tempertature properties in
Fractional Quantum Hall states. Initially proposed as a small- theory, it
was subsequently extended by Shankar to form an algebraically consistent theory
for all in the lowest Landau level. Such a theory is amenable to a
conserving approximation in which the constraints have vanishing correlators
and decouple from physical response functions. Properties of the incompressible
fractions are explored in this conserving approximation, including the
magnetoexciton dispersions and the evolution of the small- structure factor
as \nu\to\half. Finally, a formalism capable of dealing with a nonuniform
ground state charge density is developed and used to show how the correct
fractional value of the quasiparticle charge emerges from the theory.Comment: 15 pages, 2 eps figure
Slow-blue nuclear hypervariables in PanSTARRS-1
We discuss 76 large amplitude transients (Îm > 1.5) occurring in the nuclei of galaxies, nearly all with no previously known active galactic nucleus (AGN). They have been discovered as part of the Pan-STARRS1 (PS1) 3Ï survey, by comparison with Sloan Digital Sky Survey (SDSS) photometry a decade earlier, and then monitored with the Liverpool Telescope, and studied spectroscopically with the William Herschel Telescope (WHT). Based on colours, light-curve shape, and spectra, these transients fall into four groups. A few are misclassified stars or objects of unknown type. Some are red/fast transients and are known or likely nuclear supernovae. A few are either radio sources or erratic variables and so likely blazars. However the majority (âŒ66âperâcent) are blue and evolve slowly, on a time-scale of years. Spectroscopy shows them to be AGN at z ⌠0.3 â 1.4, which must have brightened since the SDSS photometry by around an order of magnitude. It is likely that these objects were in fact AGN a decade ago, but too weak to be recognized by SDSS; they could then be classed as âhypervariableâ AGN. By searching the SDSS Stripe 82 quasar database, we find 15 similar objects. We discuss several possible explanations for these slow-blue hypervariables â (i) unusually luminous tidal disruption events; (ii) extinction events; (iii) changes in accretion state; and (iv) large amplitude microlensing by stars in foreground galaxies. A mixture of explanations (iii) and (iv) seems most likely. Both hold promise of considerable new insight into the AGN phenomenon
Hamiltonian Description of Composite Fermions: Magnetoexciton Dispersions
A microscopic Hamiltonian theory of the FQHE, developed by Shankar and myself
based on the fermionic Chern-Simons approach, has recently been quite
successful in calculating gaps in Fractional Quantum Hall states, and in
predicting approximate scaling relations between the gaps of different
fractions. I now apply this formalism towards computing magnetoexciton
dispersions (including spin-flip dispersions) in the , 2/5, and 3/7
gapped fractions, and find approximate agreement with numerical results. I also
analyse the evolution of these dispersions with increasing sample thickness,
modelled by a potential soft at high momenta. New results are obtained for
instabilities as a function of thickness for 2/5 and 3/7, and it is shown that
the spin-polarized 2/5 state, in contrast to the spin-polarized 1/3 state,
cannot be described as a simple quantum ferromagnet.Comment: 18 pages, 18 encapsulated ps figure
- âŠ