17,919 research outputs found
Finite element analysis of temperature distribution using ABAQUS for a laser based tile grout sealing process
Interaction of CO2, Nd:YAG, excimer and high power diode laser (HPDL) radiation with the surface of an Al2O3/SiO2 based ceramic was found to effect significant changes in the wettability characteristics of the material. It was observed that interaction with CO2, Nd:YAG and HPDL radiation reduced the enamel contact angle from 1180 to 310, 340 and 330 respectively. In contrast, interaction with excimer laser radiation resulted an increase in the contact angle to 1210. Such changes were identified as being due to: (i) the melting and partial vitrification of the Al2O3/SiO2 based ceramic surface as a result of interaction with CO2, Nd:YAG HPDL radiation. (ii) the surface roughness of the Al2O3/SiO2 based ceramic increasing after interaction with excimer laser radiation. (iii) the surface oxygen content of the Al2O3/SiO2 based ceramic increasing after interaction with CO2, Nd:YAG and HPDL radiation. The work has shown that the wettability characteristics of the Al2O3/SiO2 based ceramic could be controlled and/or modified with laser surface treatment. In particular, whether the laser radiation had the propensity to cause surface melting. However, a wavelength dependance of the change of the wetting properties could not be deduced from the findings of this work
The characteristics of a high-power diode laser fired enamel coating on a carbon steel
Significant changes to the wettability characteristics of a common engineering carbon steel(EN8) were effected after high power diode laser (HPDL) surface treatment. These modifications havebeen investigated in terms of the changes in the surface roughness of the steel, the presence of any
surface melting, the polar component of the steel surface energy and the relative surface O2 content of the steel. The morphological and wetting characteristics of the mild steel and the enamel were determined using optical microscopy, scanning electron microscopy, X-ray photoemission spectroscopy, energy-dispersive X-ray analysis and wetting experiments by the sessile drop
technique. This work has shown that HPDL radiation can be used to alter the wetting characteristics of carbon steel so as to facilitate improved enamelling. Furthermore, standard mechanical, physical and chemical testing of the HPDL-fired enamel glaze revealed the glaze to possess similar properties to those of a conventionally fired enamel glaze in terms of bond strength, rupture /impact strength, wear and corrosion resistance. Such similar performance can be attributed to the two glazes possessing the same mechanical properties and similar amorphous structure, despite their very different firing techniques
The effects of process gas type on the surface condition of high power diode laser treated ordinary Portland cement
This paper examines the effects of using O2, Ar and He process gasses during the treatment of the ordinary Portland cement (OPC) surface of concrete with a high power diode laser (HPDL). The study revealed that, depending on the shield gas used, distinct difference existed in the surface condition of the concrete after HPDL treatment. In particular, 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 is turn was also seen to affect the cooling rate and therefore the tendency to generate microcracks
Wettability characteristics of polyethylene (PE) modified with CO2, Nd:YAG, excimer and high power diode lasers
Interaction of CO2, Nd:YAG, excimer and high power diode laser (HPDL) radiation with the surface of the bio-material, polyethylene (PE), was found to effect varying degrees of change to the wettability characteristics of the material depending upon the laser used. It was observed that interaction with CO2, Nd:YAG and HPDL effected very little change to wettability characteristics of the PE. In contrast, interaction of the PE with excimer laser radiation resulted an increase in a marked improvement in the wettability characteristics. After excimer laser treatment the surface O2 content was found to have increased and the material was seen to be more polar in nature, resulting in a significant increase in the wettability characteristics. The work has shown that the wettability characteristics of the PE could be controlled and/or modified with laser surface treatment. However, a wavelength dependence of the change of the wetting properties could not be deduced from the findings of this work
Surface glazing of concrete using a 2.5 kW high power diode lase
Interaction of CO2, Nd:YAG, excimer and high power diode laser (HPDL) radiation with the surface of an Al2O3/SiO2 based ceramic was found to affect significant changes in the wettability characteristics of the material. It was observed that interaction with CO2, Nd:YAG and HPDL radiation reduced the enamel contact angle from 1180 to 310, 340 and 330 respectively. In contrast, interaction with excimer laser radiation resulted an increase in the contact angle to 1210. Such changes were identified as being due to: (i) the melting and partial vitrification of the Al2O3/SiO2 based ceramic surface as a result of interaction with CO2, Nd:YAG HPDL radiation. (ii) the surface roughness of the Al2O3/SiO2 based ceramic increasing after interaction with excimer laser radiation. (iii) the relative surface oxygen content of the Al2O3/SiO2 based ceramic increasing after interaction with CO2, Nd:YAG and HPDL radiation. The work has shown that the wettability characteristics of the Al2O3/SiO2 based ceramic could be controlled and/or modified with laser surface treatment. Moreover, it was found that changes in the wettability characteristics of the Al2O3/SiO2 based ceramic are related to the effects of laser wavelength, that is whether the wavelength of the laser radiation has the propensity to cause surface melting
Inverse Optimization of Convex Risk Functions
The theory of convex risk functions has now been well established as the
basis for identifying the families of risk functions that should be used in
risk averse optimization problems. Despite its theoretical appeal, the
implementation of a convex risk function remains difficult, as there is little
guidance regarding how a convex risk function should be chosen so that it also
well represents one's own risk preferences. In this paper, we address this
issue through the lens of inverse optimization. Specifically, given solution
data from some (forward) risk-averse optimization problems we develop an
inverse optimization framework that generates a risk function that renders the
solutions optimal for the forward problems. The framework incorporates the
well-known properties of convex risk functions, namely, monotonicity,
convexity, translation invariance, and law invariance, as the general
information about candidate risk functions, and also the feedbacks from
individuals, which include an initial estimate of the risk function and
pairwise comparisons among random losses, as the more specific information. Our
framework is particularly novel in that unlike classical inverse optimization,
no parametric assumption is made about the risk function, i.e. it is
non-parametric. We show how the resulting inverse optimization problems can be
reformulated as convex programs and are polynomially solvable if the
corresponding forward problems are polynomially solvable. We illustrate the
imputed risk functions in a portfolio selection problem and demonstrate their
practical value using real-life data
A comparative study of the surface glaze characteristics of concrete treated with CO2 and high power diode lasers. Part I: glaze characteristics
This present work describes the differences in the characteristics of glazes generated on the ordinary
Portland cement (OPC) surface of concrete by means of CO2 and high power diode laser (HPDL)
radiation. The value of such an investigation would be to facilitate the hitherto impossible task of
generating a durable and long-lasting surface seal on the concrete, thereby extending the life and
applications base of the concrete. The basic process phenomena are investigated and the laser effects
in terms of glaze morphology, composition, phase and microstructure are presented. Also, the
resultant heat affects are analysed and described. The glaze generated after HPDL interaction was
found be fully amorphous in nature, whilst the glaze generated after CO2 laser interaction was seen to
be of a semi-amorphous structure, with sizeable areas, randomly located within the glaze, displayed a
somewhat regular columnar structure. This is proposed to be due to the differing solidification rates
occasioned by each laser after treatment as a result of differences in the beam absorption lengths
Effect of laser induced rapid solidification structures on adhesion and bonding characteristics of alumina/silica based oxide to vitreous enamel
The present work is concerned with investigating the effects of high power diode laser (HPDL) radiation on the
microstructure of an amalgamated alumina/silica based oxide compound (AOC). The main rapid solidification
theories, namely constitutional supercooling and the theory of morphological stability, are used to explain the
observed microstructural changes in the AOC resulting from HPDL interaction. Without laser treatment of the
AOC surface it was impossible to fire the enamel onto the AOC. However, wetting experiments, using a number of
control liquids and the sessile drop technique, revealed that laser treatment of the AOC surface significantly altered
the wetting characteristics of the AOC and allowed the enamel to bond to the AOC. Accordingly, HPDL treatment
was identified as allowing the vitreous enamel to wet the surface by causing a decrease in the enamel contact angle
from 118Ā° to 33Ā°. Moreover, no discernible difference was seen in the change in contact angle across the range of
rapid solidification microstructures obtained. The actual incidence of rapid surface resolidification, and not the
degree of rapid surface resolidification, was therefore identified as being the primary factor governing changes in
contact angle. The bonding mechanisms were identified as being principally owing to van derWaals forces, however,
some evidence of chemical bonding was also observed. The work has clearly shown that laser radiation can be used
to alter the wetting characteristics of the AOC
On the mechanisms of wetting characteristics modification for selected metallic materials by means of high power diode laser radiation
This work elucidates and analyses the factors responsible for modifications to the wettability characteristics of metallic materials after high power diode laser (HPDL) treatment. It was found that interaction of EN3 and EN8 mild steel with HPDL radiation resulted in the wettability characteristics of the mild steels altering to various degrees depending upon the laser processing parameters. Such changes in the wettability characteristics of the mild steels were found to be due essentially to: (i) modifications to the surface roughness; (ii) changes in the surface O2 content and (iii) the increase in the polar component of the surface energy. All of these factors were seen to influence the wettability characteristics of the mild steels, however, the degree of influence exerted by each was found to differ. Work was therefore conducted to isolate each of these influential factors, thereby allowing the magnitude of their influence to be determined. This analysis revealed that surface roughness was the primary influential factor governing changes in and hence the wettability characteristics of the mild steels. Surface energy, by way of microstructural changes, was also shown to influence to a lesser extent changes in the wettability characteristics, whilst surface O2 content, by way of process gas, was found to play a minor role in inducing changes in the wettability characteristics of the mild steels
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