Application of Optimization Techniques to the Optical Design of a Laser Seeker

This report describes the development of a computer model for the design of a laser seeker optical system. A laser seeker is a device that detects pulsed laser energy. The computer model is configured to design the seeker optics based on the following performance criteria: Sensitivity to laser energy, which can be related to target acquisition range; optical field of view; and seeker optics cross section area. The design is defined by four variables and a set of fixed parameters, and is configured using computer optimization with both a direct search and a random search being used. A superior design is selected from comparison of many sets of variables based on the value of an objective function made up of some of all of the performance criteria listed above and additional penalty factors applied for design constraint violations. The computer model contains design blocks for the detector, the preamplifier, and the optical elements of the seeker. There is also a computer ray trace routine to evaluate optical performance. The model was run with roar different objective functions, and the resulting seeker designs were analyzed. A detail listing of the computer program is contained in Appendix B

Digital Acquisition and Analysis of Acoustic Emission Signals for Crack Site Initiation Studies

In the study of elastic-plastic fracture mechanisms it is necessary to determine accurately the time and location history of crack initiation and to discriminate between the fracture mechanisms of ductile and brittle rupture. In order to accomplish this, a real-time digital acquisition system for analysis of acoustic emissions has been configured, and some preliminary results are described in this paper. The goals for this system are to locate crack initiation sites with an accuracy of 200 μm or better and to respond to events separated in time by less than 100 ms

Limitations for heterodyne detection of Brillouin scattered light

One means by which elastic properties of a material may be determined is measuring sound wave velocities in the material, from which elastic moduli of interest can be computed. Velocity can be measured by conventional piezoelectric transduction techniques, by applying laser ultrasonics, or by using Brillouin-scattering methods. Brillouin-scattering techniques for determining the sound wave velocity are particularly attractive since they are completely noninvasive. Only a probe beam of light is required since the thermal energy in the material provides the elastic motion. Heterodyne methods for detection of Brillouin-scattered light are considered one possible means to increase the speed of the scattered light frequency detection. Results of experiments with simulated Brillouin scattering suggest that heterodyne detection of the Brillouin-scattered light is feasible. Experiments to detect Brillouin-scattered light, with water as the scattering medium, were designed and interpreted using the results of the simulated scattering experiments. Overall, results showed that it is difficult to narrow the linewidth for Brillouin scattering to an acceptable level. The results given indicate that heterodyne detection of the Brillouin components requires detection bandwidths that are quite small, perhaps 10 Hz or lower. These small bandwidths can be routinely achieved using lock-in amplifier techniques

Acousto-Optic Measurement of Micromechanical Resonance for Adhesive Bond Integrity

Traditional nondestructive evaluation (NDE) of bonding flaws has generally used either ultrasound or x-rays as a directed energy source to image or otherwise detect the discontinuity of an improper bond. While this approach has broad applicability, it is inadequate where the material is highly attenuating or anisotropic, or when it is impossible to achieve an adequate interrogation due to geometrical constraints. These difficulties are seen in materials such as the silica fiber composites used for the thermal protection tiles on the Space Shuttle Orbiter, insulating rubber liners used for solid rocket motors, and rubber or foam coating materials

Laser Detection of Acoustic Displacements by Destabilizing a Frequency Stabilized Helium Neon Laser

A sensor for detecting low-amplitude acoustic displacements is described. This instrument is based on a stabilized helium-neon laser and is capable of measuring submicron displacements of diffuse surfaces at distances of up to 10 m and with a bandwidth between 0.2 and 100 kHz. The potential for extension of the technique to higher frequencies is discussed. The sensor uses the inherent sensitivity of an alternate-mode balanced, frequency-stabilized laser to small amounts of retroreflected light. Applications of the sensor include a study of bonding flaws in complex multilayer materials, such as the thermal protection tiles on the Space Shuttle Orbiter and in graphite epoxy laminar composites

Research into the Health Benefits of Sprint Interval Training Should Focus on Protocols with Fewer and Shorter Sprints

Over the past decade, it has been convincingly shown that regularly performing repeated brief supramaximal cycle sprints (sprint interval training [SIT]) is associated with aerobic adaptations and health benefits similar to or greater than with moderate-intensity continuous training (MICT). SIT is often promoted as a time-efficient exercise strategy, but the most commonly studied SIT protocol (4–6 repeated 30-s Wingate sprints with 4 min recovery, here referred to as ‘classic’ SIT) takes up to approximately 30 min per session. Combined with high associated perceived exertion, this makes classic SIT unsuitable as an alternative/adjunct to current exercise recommendations involving MICT. However, there are no indications that the design of the classic SIT protocol has been based on considerations regarding the lowest number or shortest duration of sprints to optimise time efficiency while retaining the associated health benefits. In recent years, studies have shown that novel SIT protocols with both fewer and shorter sprints are efficacious at improving important risk factors of noncommunicable diseases in sedentary individuals, and provide health benefits that are no worse than those associated with classic SIT. These shorter/easier protocols have the potential to remove many of the common barriers to exercise in the general population. Thus, based on the evidence summarised in this current opinion paper, we propose that there is a need for a fundamental change in focus in SIT research in order to move away from further characterising the classic SIT protocol and towards establishing acceptable and effective protocols that involve minimal sprint durations and repetitions

Sex Comparison of Knee Extensor Size, Strength and Fatigue Adaptation to Sprint Interval Training

Regular sprint interval training (SIT) improves whole-body aerobic capacity and muscle oxidative potential, but very little is known about knee extensor anabolic or fatigue resistance adaptations, or whether effects are similar for males and females. The purpose of this study was to compare sex-related differences in knee extensor size, torque-velocity relationship and fatigability adaptations to 12 weeks SIT.Sixteen males and fifteen females (mean (SEM) age: 41 (±2.5) yrs) completed measurements of total body composition assessed by DXA, quadriceps muscle cross-sectional area (CSAQ) assessed by MRI, the knee extensor torque-velocity relationship (covering 0 - 240°·sec) and fatigue resistance, which was measured as the decline in torque from the first to the last of 60 repeated concentric knee extensions performed at 180°·sec. SIT consisted of 4 x 20 second sprints on a cycle ergometer set at an initial power output of 175% of power at VO2max, three times per week for 12 weeks.CSAQ increased by 5% (p=0.023) and fatigue resistance improved 4.8% (p=0.048), with no sex differences in these adaptations (sex comparisons: p=0.140 and p=0.282, respectively). Knee extensor isometric and concentric torque was unaffected by SIT in both males and females (p>0.05 for all velocities).12 weeks SIT, totalling 4 minutes very intense cycling per week, significantly increased fatigue resistance and CSAQ similarly in males and females, but did not significantly increase torque in males or females. These results suggest that SIT is a time-effective training modality for males and females to increase leg muscle size and fatigue resistance

Sex differences in the effects of 12 weeks sprint interval training on body fat mass and the rates of fatty acid oxidation and VO 2 max during exercise

Abstract Background The purpose of this study was to examine whether very short duration, very high intensity sprint interval training (SIT) leads to loss of body fat mass in association with improvements to VO2max and fatty acid oxidation, and to assess the extent of sex dimorphism in these physiological responses. Methods A total of 24 men and 17 women (mean (SEM) age: 39 (±2) years; body mass index 24.6 (0.6)) completed measurements of the maximal rate of oxygen uptake (VO2max) and fatty acid oxidation (FATmax). Body fat and lean mass were measured by dual emission x-ray absorptiometry, and fasting blood lipid, glucose and insulin profiles were assessed before and after training. SIT consisted of 4×20 s sprints on a cycle ergometer at approximately 175% VO2max, three times per week for 12 weeks. Results Fat mass decreased by 1.0 kg, although men lost statistically significantly more fat than women both when expressed in Kg and as % body fat. VO2max increased by around 9%, but women improved VO2max significantly more than men. FATmax improved by around 13%, but fasting plasma glucose, insulin, total triglyceride, total cholesterol and high-density lipoprotein (HDL) did not change after training, while low-density lipoprotein decreased by 8% (p=0.028) and the HDL:Total Cholesterol ratio improved by 6%. There were no sex differences in these metabolic responses to training. Conclusions These results show lower body fat %, and higher rates of fatty acid oxidation and VO2max after 12 weeks of training for just 4 min per week. Notably, women improved VO2max more than men, while men lost more fat than women

Fibre-Specific Responses to Endurance and Low Volume High Intensity Interval Training: Striking Similarities in Acute and Chronic Adaptation

The current study involved the completion of two distinct experiments. Experiment 1 compared fibre specific and whole muscle responses to acute bouts of either low-volume high-intensity interval training (LV-HIT) or moderate-intensity continuous endurance exercise (END) in a randomized crossover design. Experiment 2 examined the impact of a six-week training intervention (END or LV-HIT; 4 days/week), on whole body and skeletal muscle fibre specific markers of aerobic and anaerobic capacity. Six recreationally active men (Age: 20.7±3.8 yrs; VO2peak: 51.9±5.1 mL/kg/min) reported to the lab on two separate occasions for experiment 1. Following a muscle biopsy taken in a fasted state, participants completed an acute bout of each exercise protocol (LV-HIT: 8, 20-second intervals at ∼170% of VO2peak separated by 10 seconds of rest; END: 30 minutes at ∼65% of VO2peak), immediately followed by a muscle biopsy. Glycogen content of type I and IIA fibres was significantly (p<0.05) reduced, while p-ACC was significantly increased (p<0.05) following both protocols. Nineteen recreationally active males (n = 16) and females (n = 3) were VO2peak-matched and assigned to either the LV-HIT (n = 10; 21±2 yrs) or END (n = 9; 20.7±3.8 yrs) group for experiment 2. After 6 weeks, both training protocols induced comparable increases in aerobic capacity (END: Pre: 48.3±6.0, Mid: 51.8±6.0, Post: 55.0±6.3 mL/kg/min LV-HIT: Pre: 47.9±8.1, Mid: 50.4±7.4, Post: 54.7±7.6 mL/kg/min), fibre-type specific oxidative and glycolytic capacity, glycogen and IMTG stores, and whole-muscle capillary density. Interestingly, only LV-HIT induced greater improvements in anaerobic performance and estimated whole-muscle glycolytic capacity. These results suggest that 30 minutes of END exercise at ∼65% VO2peak or 4 minutes of LV-HIT at ∼170% VO2peak induce comparable changes in the intra-myocellular environment (glycogen content and signaling activation); correspondingly, training-induced adaptations resulting for these protocols, and other HIT and END protocols are strikingly similar

Photonic Band Engineering In 1D Photonic Crystals

Achieving lasing in solid-state organic diodes has been a long-standing research priority since the first demonstrations of electroluminescence in organic devices in the 1980s. During this time, improvements to manufacturing and materials have made organic light-emitting diodes (OLEDs) commercially viable and have enabled their current use in smartphone screens and displays. Our work uses optical microcavity resonators to control the light emission from OLED devices, resulting in significant narrowing of the emission peak and control of the observed color and linewidth. In an exact analogy to the formation of electronic bands from solid-state theory, we demonstrate that coupling N multiple OLED resonators results in the splitting of the single emission peak into N multiple peaks. This hybrid multi-device structure therefore constitutes a 1-dimensional photonic crystal with a well-defined photonic energy band structure defined by the periodicity of the material layers. We show that this band structure can be manipulated by adjusting the mirror thickness to control the bandwidth and energy of the band center. We further demonstrate the formation of a photonic band gap through the introduction of a Peierls distortion to the photonic crystal lattice. By precise control of the photonic crystal structure, we seek to promote emission into a single mode and explore the possibility of reaching the lasing threshold within such photonic crystals