Contrasting the beam interaction characteristics of selected lasers with a partially stabilised zirconia (PSZ) bio-ceramic

Differences in the beam interaction characteristics of a CO2 laser, a Nd:YAG laser, a high power diode laser (HPDL) and an excimer laser with a partially stabilised zirconia (PSZ) bio-ceramic have been studied. A derivative of Beer-Lambert’s law was applied and the laser beam absorption lengths of the four lasers were calculated as 33.55 x 10-3 cm for the CO2 laser, 18.22 x 10-3 cm for the Nd:YAG laser, 17.17 x 10-3 cm for the HPDL and 8.41 x 10-6 cm for the excimer laser. It was determined graphically that the fluence threshold values at which significant material removal was effected by the CO2 laser, the Nd:YAG laser, the HPDL and the excimer laser were 52 J/cm2, 97 J/cm2, 115 J/cm2 and 0.48 J/cm2 respectively. The thermal loading value for the CO2 laser, the Nd:YAG laser, the HPDL and the excimer laser were calculated as being 1.55 kJ/cm3, 5.32 kJ/cm3, 6.69 kJ/cm3 and 57.04 kJ/cm3 respectively

Overcoming the boundary layer turbulence at Dome C: ground-layer adaptive optics versus tower

The unique atmospheric conditions present at sites such as Dome C on the Antarctic plateau are very favorable for high spatial resolution astronomy. At Dome C, the majority of the optical turbulence is confined to a 30 to 40 m thick stable boundary layer that results from the strong temperature inversion created by the heat exchange between the air and the ice-covered ground. To fully realize the potential of the exceptionally calm free atmosphere, this boundary layer must be overcome. In this article we compare the performance of two methods proposed to beat the boundary layer: mounting a telescope on a tower that physically puts it above the turbulent layer, and installing a telescope at ground level with a ground-layer adaptive optics system. A case is also made to combine these two methods to further improve the image quality

Low speed and angle of attack effects on sonic and near-sonic inlets

Tests of the Quiet, Clean Short-Haul Experimental Engine (QCSEE) were conducted to determine the effects of forward velocity and angle of attack on sonic and near-sonic inlet aerodynamic performance penalties and acoustic suppression characteristics. The tests demonstrate that translating centerbody and radial vane sonic inlets, and QCSEE high throat Mach number inlets, can be designed to operate effectively at forward speed and moderate angle of attack with good performance and noise suppression capability. The test equipment and procedures used in conducting the evaluation are described. Results of the tests are presented in tabular form

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

Single-stage sealing of ceramic tiles by means of high power diode laser radiation

An investigation has been carried out using a 60 W high power diode laser (HPDL) to determine the feasibility of sealing the void between adjoining ceramic tiles with a specially developed grout material. A single-stage process has subsequently been devised using a new grout material which consists of two distinct components: a crushed ceramic tile mix substrate and a glazed enamel surface; the crushed ceramic tile mix provides a tough, inexpensive bulk substrate, whilst the enamel provides an impervious surface glaze. HPDL processing has resulted in crack and porosity free seals produced in normal atmospheric conditions. The single-stage grout is simple to formulate and easy to apply. Tiles were successfully sealed with power densities as low as 750 W/cm2 and at rates of up to 420 mm/min. Bonding of the enamel to the crushed ceramic tile mix was identified as being primarily due to van der Waals forces and, on a very small scale, some of the crushed ceramic tile mix material dissolving into the glaze

Two energy scales and slow crossover in YbAl3

Experimental results for the susceptibility, specific heat, 4f occupation number, Hall effect and magnetoresistance for single crystals of YbAl$_{3}$ show that, in addition to the Kondo energy scale $k_{B}T_{K}$ $$ 670K, there is a low temperature scale $T_{coh}<50$K for the onset of coherence. Furthermore the crossover from the low temperature Fermi liquid regime to the high temperature local moment regime is slower than predicted by the Anderson impurity model. These effects may reflect the behavior of the Anderson Lattice in the limit of low conduction electron density.Comment: Ten pages, including three figure

Flavor changing interactions mediated by scalars at the weak scale

The quark and lepton mass matrices possess approximate flavor symmetries. Several results follow if the interactions of new scalars possess these approximate symmetries. Present experimental bounds allow these exotic scalars to have a weak scale mass. The Glashow-Weinberg criterion is rendered unnecessary. Finally, rare leptonic B meson decays provide powerful probes of these scalars, especially if they are leptoquarks.Comment: 13 pages, report LBL-3234

High power diode laser surface glazing of concrete

This present work describes the utilisation of the relatively novel high power diode laser (HPDL) to generate a surface glaze on the ordinary Portland cement (OPC) surface of concrete. 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 and microstructure are presented. Also, the resultant heat affects are analysed and described, as well as the effects of the shield gases, O2 and Ar, during laser processing. HPDL glazing of OPC was successfully demonstrated with power densities as low as 750 W cm-2 and at scanning rates up to 480 mm min-1. The work showed that the generation of the surface glaze resulted in improved mechanical and chemical properties over the untreated OPC surface of concrete. Both untreated and HPDL glazed OPC were tested for pull-off strength, rupture strength, water absorption, wear resistance and corrosion resistance. The OPC laser glaze exhibited clear improvements in wear, water sorptivity, and resistance (up to 80% concentration) to nitric acid, sodium hydroxide and detergent. Life assessment testing revealed that the OPC laser glaze had an increase in actual wear life of 1.3 to 14.8 times over the untreated OPC surface of concrete, depending upon the corrosive environment

Difficult encounters around "monkey cheeks": Farmers' interests and the design of flood retention areas in Thailand

Flood retention areas are being increasingly promoted for flood risk management. People living in these areas will accept them if their interests are taken into account. The present study analyses the extent to which farmers' interests were taken into account in two flood retention projects in Thailand. A feasibility study was conducted in preparation for the first project which included public participation. The second project was a pilot project implemented in the same zone at a small scale. Participants in the public participation process and farmers living in proposed flood retention areas were interviewed for the purpose of the present study. Agreement could have been reached between the farmers and the public agencies concerning the flood retention areas. However, the participation process did not enable frank discussion about the conditions under which farmers would accept the project. The second project was designed without public participation and offered very little compensation to farmers. In countries marked by power imbalances in water resources management, public agencies may impose flood retention areas, but the absence of agreements with farmers can reduce the effectiveness of the measure. Reaching such agreements requires challenging the imbalanced power relationships between farmers and public agencies

The Transition from Heavy Fermion to Mixed Valence in Ce1-xYxAl3: A Quantitative Comparison with the Anderson Impurity Model

We present a neutron scattering investigation of Ce1-xYxAl3 as a function of chemical pressure, which induces a transition from heavy-fermion behavior in CeAl3 (TK=5 K) to a mixed-valence state at x=0.5 (TK=150 K). The crossover can be modeled accurately on an absolute intensity scale by an increase in the k-f hybridization, Vkf, within the Anderson impurity model. Surprisingly, the principal effect of the increasing Vkf is not to broaden the low-energy components of the dynamic magnetic susceptibility but to transfer spectral weight to high energy.Comment: 4 pages, 5 figure