685 research outputs found
Addressing effective construction logistics through the lens of vehicle movements
Purpose – Construction logistics is an essential part of construction supply chain management (CSCM). However, limited attention has been paid to this issue in the New Zealand construction industry. The purpose of this paper is to contribute to the knowledge about what hampers efficiency in transporting construction materials and plants to a construction site. The intention is to gain detailed understanding of the practice and obstacles in efficient construction logistics and thus identify interventions to improve logistics efficiency, especially using the numbers of vehicle movements to the construction site as an indicator. Design/methodology/approach – A case study approach was adopted with on-site observations and interviews. Observations were performed during constructions on-site from the start of construction to “hand-over” to the building owner. A selection of construction suppliers and subcontractors involved in the studied project were interviewed. Findings – Data analysis suggested that cost-related factors affecting the construction logistics, both monetary and non-monetary factors were not measured and largely ignored, especially the possible environmental and/or social impact occurred by the truck movement. Factors in the service-related sector were insufficiently managed in the observed site. The main contribution to inefficient construction logistics are related to understanding and implementing CSCM. It is noticed that there is inadequate awareness of CSCM and logistics efficiency largely due to lack of commitment from the management level and skills at the operational level. Originality/value – Significant intrinsic and extrinsic interventions necessary to enhance construction logistics were acknowledged from the data analysis. These include both qualitative and quantitative data. These intrinsic and extrinsic interventions, such as implementing appropriate logistics tools that suits individual site and introducing traffic management costs, offer plausible explanations regarding how to improve the efficiency in construction logistics through optimising transportation movements to the construction site
Explosion mechanism of core-collapse supernovae: role of the Si/O interface
We present a simple criterion to predict the explodability of massive stars
based on the density and entropy profiles before collapse. If a pronounced
density jump is present near the Si/Si-O interface, the star will likely
explode. We develop a quantitative criterion by using 1D
simulations where -driven turbulence is included via time-dependent
mixing-length theory. This criterion correctly identifies the outcome of the
supernova more than of the time. We also find no difference in how this
criterion performs on two different sets of progenitors, evolved using two
different stellar evolution codes: FRANEC and KEPLER. The explodability as a
function of mass of the two sets of progenitors is very different, showing: (i)
that uncertainties in the stellar evolution prescriptions influence the
predictions of supernova explosions; (ii) the most important properties of the
pre-collapse progenitor that influence the explodability are its density and
entropy profiles. We highlight the importance that -driven turbulence
plays in the explosion by comparing our results to previous works.Comment: 20 pages, 12 figures, submitted to Ap
Size-Dependent Surface Plasmon Dynamics in Metal Nanoparticles
We study the effect of Coulomb correlations on the ultrafast optical dynamics
of small metal particles. We demonstrate that a surface-induced dynamical
screening of the electron-electron interactions leads to quasiparticle
scattering with collective surface excitations. In noble-metal nanoparticles,
it results in an interband resonant scattering of d-holes with surface
plasmons. We show that this size-dependent many-body effect manifests itself in
the differential absorption dynamics for frequencies close to the surface
plasmon resonance. In particular, our self-consistent calculations reveal a
strong frequency dependence of the relaxation, in agreement with recent
femtosecond pump-probe experiments.Comment: 8 pages + 4 figures, final version accepted to PR
Spaceflight Payload Design, Flight Experience G-408
Worcester Polytechnic Institute\u27s first payload of spaceflight experiments flew aboard Columbia, STS-40, during June of 1991 and culminated eight years of work by students and faculty. The Get Away Special (GAS) payload was installed on the GAS bridge assembly at the aft end of the cargo bay behind the Spacelab Life Sciences (SLS-l) laboratory. The experiments were turned on by astronaut signal after reaching orbit and then functioned for 72 hours. Environmental and experimental measurements were recorded on three cassette tapes which, together with zeolite crystals grown on orbit, formed the basis of subsequent analyses.
The experiments were developed over a number of years by undergraduate students meeting their project requirements for graduation. The experiments included zeolite crystal growth, fluid behavior, and microgravity acceleration measurement in addition to environmental data acquisition. Preparation also included structural design, thermal design, payload integration, and experiment control.
All of the experiments functioned on orbit and the payload system performed within design estimates
Amelioration of renal damage by administration of anti-thymocyte globulin to potential donors in a brain death rat model
Brain death (BD), a non-immunological factor of renal injury, triggers an inflammatory process causing pathological signs of cell death in the kidney, such as necrosis and apoptosis. Kidneys from brain dead donors show lower success rates than kidneys from living donors and one strategy to improve transplantation outcome is to precondition the donors. For the first time, anti-rat thymoglobulin (rATG) was administered in an experimental brain death animal model to evaluate if it could ameliorate histopathological damage and improve organ function. Animals were divided into three groups: V (n = 5) ventilated for 2 h; BD (n = 5) brain death and ventilated for 2 h; and BD+rATG (n = 5) brain death, ventilated for 2 h, rATG was administered during brain death (10 mg/kg). We observed lower creatinine levels in treatment groups (means): V, 0·88 ± 0·22 mg/dl; BD, 1·37 ± 0·07 mg/dl; and BD+rATG, 0·64 ± 0·02 mg/dl (BD versus BD+rATG, P < 0·001). In the BD group there appeared to be a marked increase of ATN, whereas ATN was decreased significantly in the rATG group (V, 2·25 ± 0·5 versus BD, 4·75 ± 0·5, P < 0·01; BD+rATG, 2·75 ± 0·5 versus BD 4·75 ± 0·5 P < 0·01). Gene expression was evaluated with reverse transcription–polymerase chain reaction; tumour necrosis factor (TNF)-α, interleukin (IL)-6, C3, CD86 showed no significant difference between groups. Increased IL-10 and decreased CCL2 in BD+rATG compared to BD (both cases P < 0·01). Myeloperoxidase was increased significantly after the brain death setting (V: 32 ± 7·5 versus BD: 129 ± 18). Findings suggest that rATG administered to potential donors may ameliorate renal damage caused by BD. These findings could contribute in the search for specific cytoprotective interventions to improve the quality and viability of transplanted organs.Facultad de Ciencias Médica
Size-dependent Correlation Effects in Ultrafast Optical Dynamics of Metal Nanoparticles
We study the role of collective surface excitations in the electron
relaxation in small metal particles. We show that the dynamically screened
electron-electron interaction in a nanoparticle contains a size-dependent
correction induced by the surface. This leads to new channels of quasiparticle
scattering accompanied by the emission of surface collective excitations. We
calculate the energy and temperature dependence of the corresponding rates,
which depend strongly on the nanoparticle size. We show that the
surface-plasmon-mediated scattering rate of a conduction electron increases
with energy, in contrast to that mediated by a bulk plasmon. In noble-metal
particles, we find that the dipole collective excitations (surface plasmons)
mediate a resonant scattering of d-holes to the conduction band. We study the
role of the latter effect in the ultrafast optical dynamics of small
nanoparticles and show that, with decreasing nanoparticle size, it leads to a
drastic change in the differential absorption lineshape and a strong frequency
dependence of the relaxation near the surface plasmon resonance. The
experimental implications of our results in ultrafast pump-probe spectroscopy
are also discussed.Comment: 29 pages including 6 figure
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