Ballistic Electron Emission Microscopy (BEEM) and finite‐element electrostatic modeling were used to quantify how “small‐size” effects modify the energy barrier at metal/semiconductor nanostructure nanocontacts, f...
Ballistic Electron Emission Microscopy (BEEM) and finite‐element electrostatic modeling were used to quantify how “small‐size” effects modify the energy barrier at metal/semiconductor nanostructure nanocontacts, formed by making Schottky contacts to cleaved edges of GaAs quantum wells (QWs). The Schottky barrier height over the QWs was found to systematically increase with decreasing QW width, by up to ∼140 meV for a 1nm QW. This is mostly due to a large quantum‐confinement increase (∼200 meV for a 1nm QW), modified by smaller decreases due to “environmental” electric field effects. Our modeling gives excellent quantitative agreement with measurements for a wide range of QW widths when both quantum confinement and environmental electric fields are considered.
The use of Fiber Optic sensors for structural monitoring applications has attained popularity among researchers and practitioners recently due to their immense advantages. This paper discusses a continuous structural ...
The use of Fiber Optic sensors for structural monitoring applications has attained popularity among researchers and practitioners recently due to their immense advantages. This paper discusses a continuous structural monitoring technique using surface mounted and embedded fiber optic strain sensors to measure the strain in FRP bridge decks. An Extrinsic Fabry‐Perot Interferometric (EFPI) strain sensor was selected for evaluation as it offers a good compromise between accuracy and cost considerations. This EFPI strain sensor, along with a conventional strain gauge, was surface mounted on a FRP bridge decks. The decks were then subjected to an accelerated aging test in an environmental chamber and the performance of both the strain sensors was recorded for a performance comparison. The results from the seven months of accelerated aging that is equivalent to 10 years of actual life show that the strain gauge sensor and the EFPI Fiber Optic sensor are still in working condition. The EFPI fiber optic sensor detects minute and sudden changes in strain more effectively than the strain gauge sensor. Placement in the environmental chamber did not affect the EFPI sensor’s performance and is an indication of its applicability to field structural monitoring for lengthy periods of time. The second part is a preliminary work where a fiber optic sensor was embedded inside a FRP plate during the pultrusion process. This shows the feasibility of manufacturing FRP bridge decks with embedded fiber optic sensors.
The popularity of FRP bridge decks has increased in recent times because of their high strength to weight ratio, fatigue resistance etc. Defects due to degradation of the bridge deck malign their properties and advers...
The popularity of FRP bridge decks has increased in recent times because of their high strength to weight ratio, fatigue resistance etc. Defects due to degradation of the bridge deck malign their properties and adversely affect the structural integrity. These defects need to be detected and continuously monitored using field techniques such as infrared thermography. The process of manually analyzing the infrared images is tedious and ambiguous. Instead, using software algorithms on the infrared images of FRP decks can increase the defect detection speed and accuracy. This paper proposes a software automated defect detection technique to detect subsurface anomalies in fiber reinforced polymer (FRP) bridge decks. Thermal images of the FRP decks were captured using a radiometric infrared camera. Software algorithms using morphological image processing and fuzzy clustering techniques were developed to analyze the images for detecting the defects automatically. They were tested on infrared images of FRP bridge decks prepared in the laboratory. In the tests conducted, simulated subsurface defects of varying size, thickness and wearing surfaces were fabricated in the laboratory. The tests include a performance analysis of detecting delaminations and debonds, and the effect of distance on the detecting ability of the algorithm. The algorithms were also tested with FRP deck specimens under solar radiation, to test the response under a passive heat source. The study showed that Infrared Thermography can be effectively used to detect subsurface defects and the process can be automated with substantial accuracy.
Microwave nondestructive testing and evaluation of surface‐breaking and internal cracks in cement‐based materials, employing open‐ended rectangular waveguide probes, has the potential to be a viable approach for th...
Microwave nondestructive testing and evaluation of surface‐breaking and internal cracks in cement‐based materials, employing open‐ended rectangular waveguide probes, has the potential to be a viable approach for the purpose of structural health monitoring. This paper presents an empirical model for simulating crack characteristic signal (signal reflected by a cracked sample under test as a function of scanning distance) given the dielectric property of the material, crack dimensions, probe aperture dimensions, operating frequency and the standoff distance.
For the control of fuel channels of PHWR CANDU type, a novel type of rotating magnetic field eddy current transducer was developed, as well as the afferent electronic equipment. So, the position and the tilt of garter...
For the control of fuel channels of PHWR CANDU type, a novel type of rotating magnetic field eddy current transducer was developed, as well as the afferent electronic equipment. So, the position and the tilt of garter springs using neuro‐fuzzy network could be determined, and the presence of the discontinuities on external and internal surface of the tubes can be emphasized. A numerical code for the solving of the forward problem was developed.
During the past decade, several research groups have begun to report unique spectroscopic results for mixed gas plasma systems in which one of the species present is hydrogen gas. In these experiments, researchers hav...
During the past decade, several research groups have begun to report unique spectroscopic results for mixed gas plasma systems in which one of the species present is hydrogen gas. In these experiments, researchers have reported excessive line broadening of H emission lines and peculiar non‐Boltzmann population of excited hydrogen states. The hydrogen line broadening in these studies has been attributed to Doppler broadening associated with anomalously high random translational velocity of H atoms (i.e. fast hydrogen). The spectroscopic data suggest the presence of a newly identified regime of energetic mixed gas hydrogen plasma systems, called resonant transfer (RT) plasmas. The data also suggest that these RT plasma systems have unique characteristics that warrant further exploration for propulsion applications. Preliminary calculations suggest that a microwave RT plasma thruster could achieve performance several orders of magnitude greater than chemical rocket propulsion. Accordingly, the NASA Institute for Advanced Concepts (NIAC) has funded a study aimed at assessing the potential of RT plasmas for propulsion applications. This paper will discuss the results of the NIAC Phase I study including spectroscopic characterization of the RT plasma, development of RT plasma thruster hardware and preliminary test firing of two separate RT plasma thrusters.
Existing forensic techniques employed to recover obliterated serial numbers fall mainly into one of two categories, those requiring extensive sample preparation including the use of acid etchants, and those utilizing ...
Existing forensic techniques employed to recover obliterated serial numbers fall mainly into one of two categories, those requiring extensive sample preparation including the use of acid etchants, and those utilizing magnetic particles to image irregularities in surface magnetic properties. The former is time consuming and utilizes potentially harmful chemicals while the latter messy and potentially low in sensitivity. A new approach is being investigated whereby the stray magnetic field is measured using a Hall effect sensor. The sample is magnetized using an electromagnetic c‐core yoke. For increased sensitivity, an AC approach is being utilized that benefits from the use of a lock‐in amplifier. The approach has been tested on some artificial specimens and part of a real gun with the serial numbers removed by surface grinding.
The previous papers presented at STAIF 2002 and STAIF 2003 discussed the design, fabrication and characterization of the evaporator section and the initial test cell of a planar MEMS loop heat pipe based upon coherent...
The previous papers presented at STAIF 2002 and STAIF 2003 discussed the design, fabrication and characterization of the evaporator section and the initial test cell of a planar MEMS loop heat pipe based upon coherent porous silicon or “CPS” technology. The potentially revolutionary advantage of CPS technology is that it is planar and allows for pores or capillaries of absolutely uniform diameter. Coherent porous silicon can be mass‐produced by various MEMS fabrication techniques. The preliminary experiments made with the original test structure exhibited the desired temperature and pressure differences, but these differences were extremely small and oscillatory. This paper describes modifications made to the initial test cell design, which were intended to improve its evacuated, closed loop performance. Included among these changes were the redesign of the compensation chamber and condenser, an increase in the porosity of the coherent porous silicon wick, the fabrication of silicon top “hot” plates with an increased depth of the vapor reservoir and the integration of metal resistive heater elements onto the backside of the top plates to simulate the input heat. Some changes were made in the test sequence to produce more discernable differences in temperatures and pressures. The most recent results of the tests made with the modified system will be presented.
A new coherent soft X‐ray branchline at the advanced light source has begun operation. Using the third harmonic from an 8 cm period undulator, this branch delivers coherent soft x‐rays ranging from 200eV to 1000eV. ...
A new coherent soft X‐ray branchline at the advanced light source has begun operation. Using the third harmonic from an 8 cm period undulator, this branch delivers coherent soft x‐rays ranging from 200eV to 1000eV. Here the beamline layout and Airy patterns generated by single pinhole diffraction at 500 eV and 600 eV are presented.
Nd:YAG pulse laser was used to ignite powdered and preheated PETN. To enhance efficiency of laser absorption by PETN, it was mixed with a small amount of carbon black powder. In this study, we will propose two‐pulse ...
Nd:YAG pulse laser was used to ignite powdered and preheated PETN. To enhance efficiency of laser absorption by PETN, it was mixed with a small amount of carbon black powder. In this study, we will propose two‐pulse laser ignition method, the first pulse is a long pulse to heat up PETN up to melting point, then second laser to ignite the heated PETN. By adopting this procedure, second short pulse laser energy can be reduced to ensure that the energy can be transferred by relatively slender plastic optical fiber. To simulate the slow laser heating process by long pulse laser, high‐power cw YAG laser up to 30W was used. While two ns‐YAG laser of about 200 mJ/pulse with 4 ns and 12 ns were used for ignition. Higher peak power with donut‐like profile laser beam of 4 ns duration gives damage to fibers, while lower peak power with relatively flat profile laser beam of 12 ns duration can safely pass through optical fiber of 1 mm diameter. We performed a series of melting experiments of PETN under normal optical microscope. From these experiments, the experimental conditions and time to the onset of PETN melting was determined. Then the ignition experiments were performed by choosing a delay time between two laser irradiation timing as a parameter. Shortest detonation delay was evidenced at the delay time close to the time that the PETN specimen is almost starting to melt.
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