Percussion drilling and trepanning are two laser drilling methods. Percussion drilling is accomplished by focusing the laser beam to approximately the required diameter of the hole, exposing the material to one or a series of laser pulses at the same spot to melt and vaporize the material. Drilling by trepanning involves cutting a hole by rotating a laser beam with an optical element or an x–y galvo-scanner. Optical trepanning is a new laser drilling method using an annular beam. The annular beams allow numerous irradiance profiles to supply laser energy to the workpiece and thus provide more flexibility in affecting the hole quality than a traditional circular laser beam. Heating depth is important for drilling application. Since there are no good ways to measure the temperature inside substrate during the drilling process, an analytical model for optical trepanning has been developed by considering an axisymmetric, transient heat conduction equation, and the evolutions of the melting temperature isotherm, which is referred to as the melt boundary in this study, are calculated to investigate the influences of the laser pulse shapes and intensity profiles on the hole geometry. This mathematical model provides a means of understanding the thermal effect of laser irradiation with different annular beam shapes. To take account of conduction in the solid, vaporization and convection due to the melt flow caused by an assist gas, an analytical two-dimensional model is developed for optical trepanning. The influences of pulse duration, laser pulse length, pulse repetition rate, intensity profiles and beam radius are investigated to examine their effects on the recast layer thickness, hole depth and taper. The ray tracing technique of geometrical optics is employed to design the necessary optics to transform a Gaussian laser beam into an annular beam of different intensity profiles. Such profiles include half Gaussian with maximum intensities at the inner and outer surfaces of the annulus, respectively, and full Gaussian with maximum intensity within the annulus. Two refractive arrangements have been presented in this study. Geometric optics, or ray optics, describes light propagation in terms of rays. However, it is a simplification of optics, and fails to account for many important optical effects such as diffraction and polarization. The diffractive behaviors of this optical trepanning system are stimulated and analyzed based on the Fresnel diffraction integral. Diffraction patterns of the resulting optical system are measured using a laser beam analyzer and compared with the theoretical results. Based on the theoretical and experimental results, the effects of experimental parameters are discussed. We have designed the annular beam shaping optical elements and the gas delivery system to construct an optical trepanning system. Laser drilling experiments are performed on the Stainless Steel-316 (SS 316) plate and the Inconel 718 (IN 718) plate. The geometry of the trepanning holes with different sizes is presented in this study.

In an attempt to mitigate the effects of the atmosphere on the coherence of an optical (laser) beam, interest has recently been shown in changing the beam shape to determine if a different power distribution at the transmitter will reduce the effects of the random fluctuations in the refractive index. Here, a model is developed for the field of a flattened Gaussian beam as it propagates through atmospheric turbulence, and the resulting effects upon the scintillation of the beam and upon beam wander are determined. A comparison of these results is made with the like effects on a standard TEM00 Gaussian beam. The theoretical results are verified by comparison with a computer simulation model for the flattened Gaussian beam. Further, a determination of the probability of fade and of mean fade time under weak fluctuation conditions is determined using the widely accepted lognormal model. Although this model has been shown to be somewhat optimistic when compared to results obtained in field tests, it has value here in allowing us to compare the effects of atmospheric conditions on the fade statistics of the FGB with those of the lowest order Gaussian beam. The effective spot size of the beam, as it compares to the spot size of the lowest order Gaussian beam, is also analyzed using Carter's definition of spot size for higher order Gaussian beams.

Very limited research studies have been conducted to examine bond of glass fibre reinforced polymer (GFRP) bars with high concrete strength. The current research project aims to compare between bond measured from a pull-out test and a hinged beam test for GFRP bars embedded in high strength concrete. Different parameters influencing bond such as GFRP bar diameter, embedment length and surface configuration were investigated in both test methods, while the bar position, i.e. top or bottom, was only studied in hinged beams. Seventy-two pull-out cubes, eight pull-out prisms and twenty-four hinged beams reinforced with GFRP bars were constructed and tested to failure. Twelve pull-out cubes and four hinged beams reinforced with steel bars were also tested for comparison purposes. The results showed that bond stress – slip curves obtained from various testing methods were similar, consisting of high initial stiffness, followed by nonlinear ascending and softening branches. In addition, it was found that the experimental bond strength obtained from hinged beams was higher than both bond strengths measured by the pull-out cube and pull-out prism. However, when a finite element analysis was conducted for hinged beams, it was shown that the tensile force in the reinforcing bar estimated by equilibrium conditions is overestimated as the large deformation of hinged beams at failure was not considered. Therefore, if the tensile force obtained from the finite element analysis is used to calculate the bond strength, it would be similar to that obtained from pull-out cube and prism. Moreover, it was found that the distribution of tensile and bond stresses was nonlinear along the GFRP embedment length and bond stress at the vicinity of the free end increased with increasing the load due to redistribution of bond stresses along the embedment length. Bond strengths were compared against the prediction methods provided in ACI-440.1R, CSA-S806, CSA-S6 and JSCE 1997. In general, all design codes showed conservative results for all specimens tested and ACI predictions gave a good agreement with experimental data compared to other codes. Artificial neural network models were developed to predict bond strength of GFRP bars in concrete. These models used bar diameter, embedment length, concrete compressive strength and concrete cover as input variables. The developed ANN models showed to be able to predict bond strength of GFRP bars in concrete and, therefore, were used to conduct a parametric study. / Higher Education Institute, Government of Libya

It is reasonable to assume that an aircraft might experience some in-flight discrete source damage caused by various incidents. It is, thus, necessary to evaluate the impact of such damage on the performance of the aircraft. This study is focused on evaluating the effect of a simple discrete damage in an aircraft wing on its static and dynamic response. The damaged wing is modeled by a thin-walled beam with a longitudinal crack the response of which can be obtained analytically. As uncertainties are present in the location and size of the crack as well as in the applied loads, their effects are incorporated into the framework consisting of structural response, crack propagation and aeroelasticity. The first objective of this study is to examine the effect of damage represented by a crack on the wing flexibility that influences its deformation and aero-elastic divergence characteristics. To study this, the thin-walled beam is modeled by Benscoter thin-walled beam theory combined with Gunnlaugsson and Pedersen compatibility conditions to accurately account for the discontinuity at the interface of the cracked and uncracked beam segments. Instead of conducting a detailed finite element analysis, the solution is obtained in an exact sense for general distributed loads representing the wind pressure effects. This analytical approach is shown to provide very accurate values for the global beam response compared with the detailed finite element shell analysis. This analytical solution is, then, used to study the beam response probabilistically. The crack location and size are assumed to be uncertain and are, thus, characterized by random variable. For a specified limit state, the probability of failure can be conveniently calculated by the first order second moment analysis using the safety index approach. The same analytical solution is also used to study the aero-elastic divergence characteristics of a wing, the inner structure of which is represented by a thin-walled beam with a crack of uncertain size and position along the beam. The second objective of this study is to examine the time growth of a crack under dynamic gust type of loading to which a wing is likely to be exposed during flight. Damage propagating during operation further deteriorates the safety of the aircraft and it is necessary to study its time growth so that its impact on the performance can be evaluated before it reaches its unstable state. The proposed framework for the crack growth analysis is based on classical fracture mechanics where the remaining flight time is obtained by Monte Carlo simulation in which various uncertainties are taken into account. To obtain equivalent cyclic loading required for crack growth analysis, random vibration analysis of the thin-walled beam is conducted for stochastic wind load defined by a gust load spectral density function. The probability of failure represented by the crack size approaching the critical crack size within the flight duration or the remaining flight time before a crack reaches its limiting value are obtained. This study with a simple representation of a wing and damage is anticipated to provide initial guidance for future studies to examine the impact of discrete source damage on the in-flight performance of the aircrafts, with the ultimate goal of minimizing the adverse effect and enhancing the safety of aircrafts experiencing damage. / Ph. D.

Yes / Although the depth of reinforced concrete deep beams is much higher than that of slender beams, extensive existing tests on deep beams have focused on simply supported beams with a scaled depth below 600 mm. In the present paper, test results of 12 two-span reinforced concrete deep beams are reported. The main parameters investigated were the beam depth, which is varied from 400 mm to 720 mm, concrete compressive strength and shear span-tooverall depth ratio. All beams had the same longitudinal top and bottom reinforcement and no web reinforcement to assess the effect of changing the beam depth on the shear strength of such beams. All beams tested failed owing to a significant diagonal crack connecting the edges of the load and intermediate support plates. The influence of beam depth on shear strength was more pronounced on continuous deep beams than simple ones and on beams having higher concrete compressive strength. A numerical technique based on the upper bound analysis of the plasticity theory was developed to assess the load capacity of continuous deep beams. The influence of the beam depth was covered by the effectiveness factor of concrete in compression to cater for size effect. Comparisons between the total capacity from the proposed technique and that experimentally measured in the current investigation and elsewhere show good agreement, even though the section depth of beams is varied.

No / There are several merits of mobile communication devices having multiple network interfaces as compared to traditional devices with just one interface. Smart phones these days are a true example of a mobile multi-homed communication device with heterogeneous network interfaces. Several solutions are available for unicast applications to provide seamless handover using the multiple interfaces of a multi-homed device in terrestrial networks. However, very little has been done on similar support for IP multicast mobility support for mobile satellite terminals in a ubiquitous multi-beam satellite network. Most of the schemes proposed for handovers in multi-homed devices place a lot of emphasis on maintaining the multi-homed device identity especially when the second interface joins the communication session. This increases complexity in the whole system. The issue of maintaining the multi-homed device identity plus the additional signalling messages involve are neither necessary nor desired in an IP multicast communication handover in a multi-beam satellite scenario. This paper seeks to exploit the group communication features of IP multicast (i.e., the fact that anyone can join or leave a multicast group at any time and from any location) and the multiple interfaces of a mobile Return Channel Satellite Terminal (RCST) to support IP multicast communication during handover when a mobile multi-homed RCST changes its point of attachment to the network from one satellite gateway to another.

Consideration of the reinforced concrete beam as a composite beam with incomplete interaction, the effect of principal strains in the shear span is studied. The influence of bond slip on the formation of cracks is studied both analytically and experimentally. / Thesis / Master of Engineering (ME)

<p> The atomic beam magnetic resonance technique with radioactive detection has been used to investigate the hyperfine structure of In^117m. The present research is based on the work done by Cameron (1962) who could not obtain accurate values for the hyperfine interaction constants due to the low neutron flux at the time in the McMaster reactor.</p> <p> This thesis is an account of an attempt to complete that experiment by observing the field independent direct hyperfine transitions. The theory of the experiment, the apparatus and techniques, and the method of data analysis are described. Because of the counting errors, the data are not as conclusive as had been hoped. If the resonances have, in fact, been seen, then the results are: a1/2 = -932.996 ± 0.012 Mc/sec a3/2 = -99.005 ± 0.005 Mc/sec μI = -0.25146 ± 0.00003 nuclear magnetons.</p> / Thesis / Master of Science (MSc)

Atomic beam magnetic resonance techniques have been used to investigate the properties of the 41-second isomeric state of silver-109 and the 32-minute ground state of the fission product cesium-138. A description of the apparatus and of the atomic beam method for the determination of nuclear moments is given. The results obtained for silver-109m are: I= 7/2 a(2S1/2) = 9477±13 Mc/sec μ1 (uncorrected) = 4.31±0.04 nuclear magnetons 109Δ109m = -(1.1±1.2)%. The value of the moment confirms that the proton configuration is (g9/2)^-3 7/2. In the course of this experiment, multiple quantum Zeeman transitions were observed between levels in both the F = I + 1/2 and F = I - 1/2 hyperfine multiplets. The results obtained for cesium-138 are: I =3 Δv = 1650 +650 -250 Mc/sec |μI| (uncorrected)= 0.45 +0.18 -0.07 nuclear magnetons. For these experiments simultaneous detection of both the resonant and thrown out portions of the beam was used for the first time in this laboratory. / Thesis / Doctor of Philosophy (PhD)

no / Reconfigurable beam steering using circular disc microstrip patch antenna with a ring slotis proposed. The overall dimension of the antenna is 5.4×5.4 mm2 printed on a 0.504 mm thick, Rogers RT5870 substrate with relative permittivity 2.3 and loss tangent 0.0012. The designed antenna operates at the expected 5G frequency band 60 GHz with a central coaxial probe feed. TwoNMOS switches are configured to generate three different beam patterns. Activating each switch individually results in a near 70 degree shift in the main beam direction, whereas the frequency characteristics are unchanged. The power gains are between 3.9 dB and 4.8dB for the three states of switches configurations. Simulated results in terms of return loss, peak gains and radiation pattern are presented and show a reasonable agreement at the expected 60 GHz bandfor 5G applications. / The published journal webpage is no longer available.