61,709 research outputs found
3D printing of cement composites
The aims of this study were to investigate the feasibility of generating 3D structures directly in rapid-hardening Portland cement (RHPC) using 3D Printing (3DP) technology. 3DP is a Additive Layer Manufacturing (ALM) process that generates parts directly from CAD in a layer-wise manner. 3D structures were successfully printed using a polyvinylalcohol: RHPC ratio of 3:97 w/w, with print resolutions of better than 1mm. The test components demonstrated the manufacture of features, including off-axis holes, overhangs / undercuts etc that would not be manufacturable using simple mould tools. Samples hardened by 1 day post-build immersion in water at RT offered Modulus of Rupture (MOR) values of up to 0.8±0.1MPa, and, after 26 days immersion in water at RT, offered MOR values of 2.2±0.2MPa, similar to bassanite-based materials more typically used in 3DP (1-3 MPa). Post-curing by water immersion restructured the structure, removing the layering typical of ALM processes, and infilling porosity
The potential for technology and knowledge transfers between foreign and local firms: a study of the construction industry in Ghana
Multinational corporations (MNCs) and other foreign firms can be conduits for technology and knowledge (T&K) transfer to host countries in the developing world. Most of the existing research focuses on T&K transfers through FDI and are drawn from Asia not Sub-Saharan Africa (SSA), although SSA is increasingly receiving foreign investment. There is a paucity of research that gives insights into project-level T&K transfer issues in SSA countries. Using the Ghanaian construction industry as an empirical focus, this article explores T&K transfer potential. The findings reveal significant weaknesses in T&K transfer across industry subsectors and between foreign and local firms. This arises from the potentially complementary but dissimilar resource and knowledge bases. The weaknesses are compounded by the absence of coherent government T&K development policie
Non-equilibrium umbrella sampling applied to force spectroscopy of soft matter
Physical systems often respond on a timescale which is longer than that of the measurement. This is particularly true in soft matter where direct experimental measurement, for example in force spectroscopy, drives the soft system out of equilibrium and provides a non-equilibrium measure. Here we demonstrate experimentally for the first time that equilibrium physical quantities (such as the mean square displacement) can be obtained from non-equilibrium measurements via umbrella sampling. Our model experimental system is a bead fluctuating in a time-varying optical trap. We also show this for simulated force spectroscopy on a complex soft molecule--a piston-rotaxane
Adiabatic Phase Diagram of an Ultracold Atomic Fermi Gas with a Feshbach Resonance
We determine the adiabatic phase diagram of a resonantly-coupled system of
Fermi atoms and Bose molecules confined in the harmonic trap by using the local
density approximation. The adiabatic phase diagram shows the fermionic
condensate fraction composed of condensed molecules and Cooper pair atoms. The
key idea of our work is conservation of entropy through the adiabatic process,
extending the study of Williams et al. [Williams et al., New J. Phys. 6, 123
(2004)] for an ideal gas mixture to include the resonant interaction in a
mean-field theory. We also calculate the molecular conversion efficiency as a
function of initial temperature. Our work helps to understand recent
experiments on the BCS-BEC crossover, in terms of the initial temperature
measured before a sweep of the magnetic field.Comment: 13 pages, 8 figures. In press, "Journal of the Physical Society of
Japan", Vol.76, No.
The Effect of Transfer Printing on Pentacene Thin-Film Crystal Structure
The thermal deposition and transfer Printing method had been used to produce
pentacene thin-films on SiO2/Si and plastic substrates (PMMA and PVP),
respectively. X-ray diffraction patterns of pentacene thin films showed
reflections associated with highly ordered polycrystalline films and a
coexistence of two polymorph phases classified by their d-spacing, d(001): 14.4
and 15.4 A.The dependence of the c-axis correlation length and the phase
fraction on the film thickness and printing temperature were measured. A
transition from the 15.4 A phase towards 14.4 A phase was also observed with
increasing film thickness. An increase in the c-axis correlation length of
approximately 12% ~16% was observed for Pn films transfer printed onto a PMMA
coated PET substrate at 100~120 C as compared to as-grown Pn films on SiO2/Si
substrates. The transfer printing method is shown to be an attractive for the
fabrication of pentacene thin-film transistors on flexible substrates partly
because of the resulting improvement in the quality of the pentacene film.Comment: 5 pages, 5 figure
Periodic substorm activity in the geomagnetic tail
On 19 May 1978 an anusual series of events is observed with the Quadrispherical LEPEDEA on board the ISEE-1 satellite in the Earth's geomagnetic tail. For 13 hours periodic bursts of both ions and electrons are seen in all the particle detectors on the spacecraft. On this day periodic activity is also seen on the ground, where multiple intensifications of the electrojets are observed. At the same time the latitudinal component of the interplanetary magnetic field shows a number of strong southward deflections. It is concluded that an extended period of substorm activity is occurring, which causes repeated thinnings and recoveries of the plasma sheet. These are detected by ISEE, which is situated in the plasma sheet boundary layer, as periodic dropouts and reappearances of the plasma. Comparisons of the observations at ISEE with those at IMP-8, which for a time is engulfed by the plasma sheet, indicate that the activity is relatively localized in spatial extent. For this series of events it is clear that a global approach to magnetospheric dynamics, e.g., reconnection, is inappropriate
Correlation length of hydrophobic polyelectrolyte solutions
The combination of two techniques (Small Angle X-ray Scattering and Atomic
Force Microscopy) has allowed us to measure in reciprocal and real space the
correlation length of salt-free aqueous solutions of highly charged
hydrophobic polyelectrolyte as a function of the polymer concentration ,
charge fraction and chain length . Contrary to the classical behaviour
of hydrophilic polyelectrolytes in the strong coupling limit, is strongly
dependent on . In particular a continuous transition has been observed from
to when decreased from 100% to
35%. We interpret this unusual behaviour as the consequence of the two features
characterising the hydrophobic polyelectrolytes: the pearl necklace
conformation of the chains and the anomalously strong reduction of the
effective charge fraction.Comment: 7 pages, 5 figures, submitted to Europhysics Letter
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