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The impact of market and supply configurations on the costs of tendering in the construction industry
The cost of tendering in the construction industry is widely suspected to be excessive, but there is little robust empirical evidence to demonstrate this. It also seems that innovative working practices may reduce the costs of undertaking construction projects and the consequent improvement in relationships should increase overall value for money. The aim of this proposed research project is to develop mechanisms for measuring the true costs of tendering based upon extensive in-house data collection undertaken in a range of different construction firms. The output from this research will enable all participants in the construction process to make better decisions about how to select members of the team and identify the price and scope of their obligations
Future Detection of Supernova Neutrino Burst and Explosion Mechanism
Future detection of a supernova neutrino burst by large underground detectors
would give important information for the explosion mechanism of collapse-driven
supernovae. We studied the statistical analysis for the future detection of a
nearby supernova by using a numerical supernova model and realistic Monte-Carlo
simulations of detection by the Super-Kamiokande detector. We mainly discuss
the detectability of the signatures of the delayed explosion mechanism in the
time evolution of the \anue luminosity and spectrum. For a supernova at 10
kpc away from the Earth, we find that not only the signature is clearly
discernible, but also the deviation of energy spectrum from the Fermi-Dirac
(FD) distribution can be observed. The deviation from the FD distribution
would, if observed, provide a test for the standard picture of neutrino
emission from collapse-driven supernovae. For the = 50 kpc case, the
signature of the delayed explosion is still observable, but statistical
fluctuation is too large to detect the deviation from the FD distribution. We
also propose a method for statistical reconstruction of the time evolution of
\anue luminosity and spectrum from data, by which we can get a smoother time
evolution and smaller statistical errors than a simple, time-binning analysis.
This method is useful especially when the available number of events is
relatively small, e.g., a supernova in the LMC or SMC. Neutronization burst of
's produces about 5 scattering events when = 10 kpc and this signal
is difficult to distinguish from \anue p events.Comment: 28 pages including all figures. Accepted by Astrophys.
r-Process in Prompt Supernova Explosions Revisited
We reanalyze -process nucleosynthesis in the neutron-rich ejecta from a
prompt supernova explosion of a low-mass (11 M) progenitor. A pompt
explosion is not yet ruled out as a possibility for low-mass supernova
progenitors. Moreover, there is mounting evidence that a new -process site
may be required. Hence, we assume that a prompt explosion can occur and make a
study of r-process nucleosynthesis in the supernova ejecta. To achieve a prompt
explosion we have performed a general relativistic hydrodynamic simulation of
adiabatic collapse and bounce using a relativistic nuclear-matter equation of
state. The electron fraction during the collapse was fixed at the
initial-model value. The size of the inner collapsing core was then large
enough to enable a prompt explosion to occur. Adopting the calculated
trajectories of promptly ejected material, we explicitly computed the burst of
neutronization due to electron captures on free protons in the photodissociated
ejecta after the passage of the shock. The thermal and compositional evolution
of the resulting neutron-rich ejecta originating from near the surface of
proto-neutron star was obtained. These were used in nuclear reaction network
calculations to evaluate the products of -process nucleosynthesis. We find
that, unlike earlier studies, the amount of -process material ejected per
supernova is quite consistent with observed galactic -process abundances.
Furthermore, the computed -process abundances are in good agreement with
Solar abundances of -process elements for A. This suggests that
prompt supernovae are still a viable -process site. Such events may be
responsible for the abundances of the heaviest -process nuclei.Comment: 13 pages, 8 figures, ApJ in press. Minor revisions as per referee's
suggestion
Developmental changes in effective connectivity associated with relational reasoning
Rostrolateral prefrontal cortex (RLPFC) is part of a frontoparietal network of regions involved in relational reasoning, the mental process of working with relationships between multiple mental representations. RLPFC has shown functional and structural changes with age, with increasing specificity of left RLPFC activation for relational integration during development. Here, we used dynamic causal modeling (DCM) to investigate changes in effective connectivity during a relational reasoning task through the transition from adolescence into adulthood. We examined fMRI data of 37 healthy female participants (11–30 years old) performing a relational reasoning paradigm. Comparing relational integration to the manipulation of single relations revealed activation in five regions: the RLPFC, anterior insula, dorsolateral PFC, inferior parietal lobe, and medial superior frontal gyrus. We used a new exhaustive search approach and identified a full DCM model, which included all reciprocal connections between the five clusters in the left hemisphere, as the optimal model. In line with previous resting state fMRI results, we showed distinct developmental effects on the strength of long-range frontoparietal versus frontoinsular short-range fixed connections. The modulatory connections associated with relational integration increased with age. Gray matter volume in left RLPFC, which decreased with age, partly accounted for changes in fixed PFC connectivity. Finally, improvements in relational integration performance were associated with greater modulatory and weaker fixed PFC connectivity. This pattern provides further evidence of increasing specificity of left PFC function for relational integration compared to the manipulation of single relations, and demonstrates an association between effective connectivity and performance during development. Hum Brain Mapp, 2013
Nucleosynthesis in O-Ne-Mg Supernovae
We have studied detailed nucleosynthesis in the shocked surface layers of an
Oxygen-Neon-Magnesium core collapse supernova with an eye to determining if the
conditions are suitable for r process nucleosynthesis. We find no such
conditions in an unmodified model, but do find overproduction of N=50 nuclei
(previously seen in early neutron-rich neutrino winds) in amounts that, if
ejected, would pose serious problems for galactic chemical evolution.Comment: 12 pages, 1 figure, to be published in Astrophysical Journal Letter
Exploiting the neutronization burst of a galactic supernova
One of the robust features found in simulations of core-collapse supernovae
(SNe) is the prompt neutronization burst, i.e. the first milliseconds
after bounce when the SN emits with very high luminosity mainly
neutrinos. We examine the dependence of this burst on variations in the input
of current SN models and find that recent improvements of the electron capture
rates as well as uncertainties in the nuclear equation of state or a variation
of the progenitor mass have only little effect on the signature of the
neutronization peak in a megaton water Cherenkov detector for different
neutrino mixing schemes. We show that exploiting the time-structure of the
neutronization peak allows one to identify the case of a normal mass hierarchy
and large 13-mixing angle , where the peak is absent. The
robustness of the predicted total event number in the neutronization burst
makes a measurement of the distance to the SN feasible with a precision of
about 5%, even in the likely case that the SN is optically obscured.Comment: 14 pages, 17 eps figures, revtex4 style, minor comments adde
Neutrino oscillation signatures of oxygen-neon-magnesium supernovae
We discuss the flavor conversion of neutrinos from core collapse supernovae
that have oxygen-neon-magnesium (ONeMg) cores. Using the numerically calculated
evolution of the star up to 650 ms post bounce, we find that, for the normal
mass hierarchy, the electron neutrino flux in a detector shows signatures of
two typical features of an ONeMg-core supernova: a sharp step in the density
profile at the base of the He shell and a faster shock wave propagation
compared to iron core supernovae. Before the shock hits the density step (t ~
150 ms), the survival probability of electron neutrinos is about 0.68, in
contrast to values of 0.32 or less for an iron core supernova. The passage of
the shock through the step and its subsequent propagation cause a decrease of
the survival probability and a decrease of the amplitude of oscillations in the
Earth, reflecting the transition to a more adiabatic propagation inside the
star. These changes affect the lower energy neutrinos first; they are faster
and more sizable for larger theta_13. They are unique of ONeMg-core supernovae,
and give the possibility to test the speed of the shock wave. The time
modulation of the Earth effect and its negative sign at the neutronization peak
are the most robust signatures in a detector.Comment: 14 pages, 10 figures (16 figure files). Text and graphics added for
illustration and clarification; Results unchanged. Version accepted for
publication in Physical Review
Nucleosynthesis and Clump Formation in a Core Collapse Supernova
High-resolution two-dimensional simulations were performed for the first five
minutes of the evolution of a core collapse supernova explosion in a 15 solar
mass blue supergiant progenitor. The computations start shortly after bounce
and include neutrino-matter interactions by using a light-bulb approximation
for the neutrinos, and a treatment of the nucleosynthesis due to explosive
silicon and oxygen burning. We find that newly formed iron-group elements are
distributed throughout the inner half of the helium core by Rayleigh-Taylor
instabilities at the Ni+Si/O and C+O/He interfaces, seeded by convective
overturn during the early stages of the explosion. Fast moving nickel mushrooms
with velocities up to about 4000 km/s are observed. This offers a natural
explanation for the mixing required in light curve and spectral synthesis
studies of Type Ib explosions. A continuation of the calculations to later
times, however, indicates that the iron velocities observed in SN 1987 A cannot
be reproduced because of a strong deceleration of the clumps in the dense shell
left behind by the shock at the He/H interface.Comment: 8 pages, LaTeX, 2 postscript figures, 2 gif figures, shortened and
slightly revised text and references, accepted by ApJ Letter
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