1,781 research outputs found
Planning effort as an effective risk management tool
In project management, high levels of risk are considered to be a significant obstacle for project success. This paper investigates whether improving the project plan can lead to improved success for high-risk projects. A quality of planning index was designed to explore how the presence of high risk affects the quality of planning and project success. The index includes managerial aspects such as costs, human resources, procurement and quality, as well as organizational support aspects based on organization maturity models. In a field study based on data collected from 202 project managers regarding their most recent projects, it was found that the levels of risk at the beginning of projects has no effect on their final success. Drilling down to find an explanation for this surprising phenomenon, we found that in the presence of high risk, project managers significantly improve their project plans. Hence, in high-risk projects, better project plans improve all four dimensions of project success: schedule overrun, cost overrun, technical performance and customer satisfaction. However, in low-risk projects, better project plans did not contribute to reducing schedule or cost overruns. In other words, while endless risk management tools are developed, we found that improving the project plan is a more effective managerial tool in dealing with high-risk projects. Finally, the paper presents the most common planning tools currently being used in high-risk projects
The distribution of red and blue galaxies in groups: an empirical test of the halo model
The popular halo model predicts that the power spectrum of the galaxy
fluctuations is simply the sum of the large scale linear halo-halo power
spectrum and the weighted power spectrum of the halo profile. Previous studies
have derived halo parameters from the observed galaxy correlation function.
Here we test the halo model directly for self-consistency with a minimal set of
theoretical assumptions by utilising the 2dF Galaxy Redshift Survey (2dFGRS).
We derive empirically the halo occupation and galaxy radial distributions in
the haloes of the 2dF Percolation-Inferred Galaxy Group (2PIGG) catalogue. The
mean halo occupation number is found to be well-fitted by a power-law, ~
M^b, at high masses, with b = 1.05, 0.88, 0.99 for red, blue and all galaxies
respectively (with 1-sigma errors of 15-19%). We find that the truncated NFW
profile provides a good fit to the galaxy radial distributions, with
concentration parameters c=3.9, 1.3, 2.4 for red, blue and all galaxies
respectively (with 1-sigma errors of 8-15%). Adding the observed linear power
spectrum to these results, we compare these empirical predictions of the halo
model with the observed correlation functions for these same 2dF galaxy
populations. We conclude that subject to some fine tuning it is an acceptable
model for the two-point correlations. Our analysis also explains why the
correlation function slope of the red galaxies is steeper than that of the blue
galaxies. It is mainly due to the number of red and blue galaxies per halo,
rather than the radial distribution within the haloes of the two galaxy
species.Comment: 15 pages, 15 figures. MNRAS accepted version. Adds appx. on profile
fitting; now use truncated NF
The X-Ray Background as a Probe of Density Fluctuations at High Redshift
The X-Ray Background (XRB) probes structure on scales intermediate between
those explored by local galaxy redshift surveys and by the COBE Microwave
Background measurements. We predict the large scale angular fluctuations in the
XRB, expressed in terms of spherical harmonics for a range of assumed
power-spectra and evolution scenarios. The dipole is due to large scale
structure as well as to the observer's motion (the Compton-Getting effect). For
a typical observer the two effects turn out to be comparable in amplitude. The
coupling of the two effects makes it difficult to use the XRB for independent
confirmation of the CMB dipole being due to the observer's motion. The large
scale structure dipole (rms per component) relative to the monopole is in the
range . The spread is mainly due
to the assumed redshift evolution scenarios of the X-ray volume emissivity
. The dipole's prediction is consistent with a measured dipole in
the HEAO1 XRB map. Typically, the harmonic spectrum drops with like . This behaviour allows us to discriminate a true clustering
signal against the flux shot noise, which is constant with , and may
dominate the signal unless bright resolved sources are removed from the XRB
map. We also show that Sachs-Wolfe and Doppler (due to the motion of the
sources) effects in the XRB are negligible. Although our analysis focuses on
the XRB, the formalism is general and can be easily applied to other
cosmological backgrounds.Comment: 14 pages, 3 postscript figures, available from
ftp://cass41.ast.cam.ac.uk/pub/lahav/xrb accepted for publication in MNRA
The symmetry of the spin Hamiltonian in herbertsmithite, a spin-1/2 kagom\'{e} lattice
We present magnetization measurements on oriented powder of
ZnCu(OH)Cl along and perpendicular to the orienting field. We
find a dramatic difference in the magnetization between the two directions. It
is biggest at low measurement fields or high temperatures. We show that the
difference at high temperatures must emerge from Ising-like exchange
anisotropy. This allows us to explain muon spin rotation data at in
terms of an exotic ferromagnetic ground state.Comment: 5 pages, 5 figure
Limited Range Fractality of Randomly Adsorbed Rods
Multiple resolution analysis of two dimensional structures composed of
randomly adsorbed penetrable rods, for densities below the percolation
threshold, has been carried out using box-counting functions. It is found that
at relevant resolutions, for box-sizes, , between cutoffs given by the
average rod length and the average inter-rod distance $r_1$, these
systems exhibit apparent fractal behavior. It is shown that unlike the case of
randomly distributed isotropic objects, the upper cutoff $r_1$ is not only a
function of the coverage but also depends on the excluded volume, averaged over
the orientational distribution. Moreover, the apparent fractal dimension also
depends on the orientational distributions of the rods and decreases as it
becomes more anisotropic. For box sizes smaller than the box counting
function is determined by the internal structure of the rods, whether simple or
itself fractal. Two examples are considered - one of regular rods of one
dimensional structure and rods which are trimmed into a Cantor set structure
which are fractals themselves. The models examined are relevant to adsorption
of linear molecules and fibers, liquid crystals, stress induced fractures and
edge imperfections in metal catalysts. We thus obtain a distinction between two
ranges of length scales: where the internal structure of the
adsorbed objects is probed, and where their distribution is
probed, both of which may exhibit fractal behavior. This distinction is
relevant to the large class of systems which exhibit aggregation of a finite
density of fractal-like clusters, which includes surface growth in molecular
beam epitaxy and diffusion-limited-cluster-cluster-aggregation models.Comment: 10 pages, 7 figures. More info available at
http://www.fh.huji.ac.il/~dani/ or
http://www.fiz.huji.ac.il/staff/acc/faculty/biham or
http://chem.ch.huji.ac.il/employee/avnir/iavnir.htm . Accepted for
publication in J. Chem. Phy
The Groverian Measure of Entanglement for Mixed States
The Groverian entanglement measure introduced earlier for pure quantum states
[O. Biham, M.A. Nielsen and T. Osborne, Phys. Rev. A 65, 062312 (2002)] is
generalized to the case of mixed states, in a way that maintains its
operational interpretation. The Groverian measure of a mixed state of n qubits
is obtained by a purification procedure into a pure state of 2n qubits,
followed by an optimization process based on Uhlmann's theorem, before the
resulting state is fed into Grover's search algorithm. The Groverian measure,
expressed in terms of the maximal success probability of the algorithm,
provides an operational measure of entanglement of both pure and mixed quantum
states of multiple qubits. These results may provide further insight into the
role of entanglement in making quantum algorithms powerful.Comment: 6 pages, 2 figure
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