The influence of shield gases on the surface condition of laser treated concrete

This work aims to elucidate the effects of using O2, Ar and He shield gasses during the treatment of the ordinary Portland cement (OPC) surface of concrete with a high power diode laser (HPDL). The findings showed a marked difference existed in the surface condition of the concrete after HPDL treatment depending on the shield gas used. The use of O2 as the shield gas was seen to result in glazes with far fewer microcracks and porosities than those generated with either Ar or He shield gases. Such differences were found to be due to the smaller O2 gas molecules dissolving molecularly into the open structure of the HPDL generated glaze on the OPC surface of concrete and react with the glass network to increase the fluidity of the melt. This in turn was also seen to affect the cooling rate and therefore the tendency to generate microcracks

New York and Astoria

"John Jacob Astor, the founder of the family, was truly a pioneer and a patriot… [He] was not only a builder of edifices in his adopted city but an empire builder as well.

Direct measurement of absorption-induced wavefront distortion in high optical power systems

Wavefront distortion due to absorption in the substrates and coatings of mirrors in advanced gravitational wave interferometers has the potential to compromise the operation and sensitivity of these interferometers [Opt. Lett.29, 2635-2637 (2004)OPLEDP0146-959210.1364/OL.29.002635]. We report the first direct spatially-resolved measurement, to our knowledge, of such wavefront distortion in a high optical power cavity. The measurement was made using an ultrahigh sensitivity Hartmann wavefront sensor on a dedicated test facility. The sensitivity of the sensor was λ/730, where λ=800 nm

Analysis of millimetre-wave polarization diverse multiple-input multiple-output capacity

Millimetre-waves offer the possibility of wide bandwidth and consequently high data rate for wireless communications. For both uni- and dual-polarized systems, signals sent over a link may suffer severe degradation due to antenna misalignment. Orientation robustness may be enhanced by the use of mutual orthogonality in three dimensions. Multiple-input multiple-output polarization diversity offers a way of improving signal reception without the limitations associated with spatial diversity. Scattering effects often assist propagation through multipath. However, high path loss at millimetre-wave frequencies may limit any reception enhancement through scattering. We show that the inclusion of a third orthogonal dipole provides orientation robustness in this setting, as well as in a rich scattering environment, by means of a Rician fading channel model covering all orientations for a millimetre-wave, tri-orthogonal, half-wave dipole transmitter and receiver employing polarization diversity. Our simulation extends the analysis into three dimensions, fully exploiting individual sub-channel paths. In both the presence and absence of multipath effects, capacity is observed to be higher than that of a dual-polarized system over the majority of a field of view.Nicholas P. Lawrence, Brian W.-H.Ng, Hedley J. Hansen, and Derek Abbot

Thermal noise from optical coatings in gravitational wave detectors

Gravitational waves are a prediction of Einstein's general theory of relativity. These waves are created by massive objects, like neutron stars or black holes, oscillating at speeds appreciable to the speed of light. The detectable effect on the Earth of these waves is extremely small, however, creating strains of the order of 10−21. There are a number of basic physics experiments around the world designed to detect these waves by using interferometers with very long arms, up to 4 km in length. The next-generation interferometers are currently being designed, and the thermal noise in the mirrors will set the sensitivity over much of the usable bandwidth. Thermal noise arising from mechanical loss in the optical coatings put on the mirrors will be a significant source of noise. Achieving higher sensitivity through lower mechanical loss coatings, while preserving the crucial optical and thermal properties, is an area of active research right now

The development and characteristics of a hand-held high power diode laser-based industrial tile grout removal and single-stage sealing system

As the field of laser materials processing becomes ever more diverse, the high power diode laser (HPDL) is now being regarded by many as the most applicable tool. The commercialisation of an industrial epoxy grout removal and single-stage ceramic tile grout sealing process is examined through the development of a hand-held HPDL device in this work. Further, an appraisal of the potential hazards associated with the use of the HPDL in an industrial environment and the solutions implemented to ensure that the system complies with the relevant safety standards are given. The paper describes the characteristics and feasibility of the industrial epoxy grout removal process. A minimum power density of approximately 3 kW/cm2 was found to exist, whilst the minimum interaction time, below which there was no removal of epoxy tile grout, was found to be approximately 0.5 s. The maximum theoretical removal rate that may be achievable was calculated as being 65.98 mm2/s for a circular 2 mm diameter beam with a power density of 3 kW/cm2 and a traverse speed of 42 mm/s. In addition, the characteristics of the single-stage ceramic tile grout sealing are outlined. The single-stage ceramic tile grout sealing process yielded crack and porosity free seals which were produced in normal atmospheric conditions. Tiles were successfully sealed with power densities as low as 550 W/cm2 and at rates of up to 420 mm/min. In terms of mechanical, physical and chemical characteristics, the single-stage ceramic tile grout was found to be far superior to the conventional epoxy tile grout and, in many instances, matched and occasionally surpassed that of the ceramic tiles themselves

Interactions of flexible polymers and globular colloids : understanding protein partitioning in two-phase aqueous polymer systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1992.Science hard copy is bound in 1 v.Includes bibliographical references (leaves 364-377).by Nicholas L. Abbott.Ph.D

La nature de l'opinion publique : Extrait de Public opinion and popular government, New York, Longman et Green, 1913, p. 3-27

Bien qu’antérieur à l’avènement des sondages, Public Opinion and Popular Government, paru en 1913, tente de comprendre le mouvement qui pousse irrésistiblement le concept d' « opinion publique » vers la mesure quantitative. C'est pour le moins l'un des enjeux de l'extrait proposé ici et c'est aussi pourquoi Lowell apparait aujourd'hui comme un grand théoricien de l'opinion publique. Dans une démarche analytique, l'auteur isole les éléments associés à l'opinion publique pour déterminer quels sont ses traits les plus fondamentaux (...)

Application of the Kissimmee River Hydraulic Model and Floodplain Spatial Analysis Tool to the Development of Floodplain Inundation Targets for the Kissimmee River Restoration Project

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv