Browsing by Subject "intrusion"
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Item Buried fiber optic intrusion sensor(Texas A&M University, 2004-09-30) Maier, Eric WilliamA distributed fiber optic intrusion sensor capable of detecting intruders from the pressure of their weight on the earth's surface was investigated in the laboratory and in field tests. The presence of an intruder above or in proximity to the buried sensor induces a phase shift in light propagating along the fiber which allows for the detection and localization of intrusions. Through the use of an ultra-stable erbium-doped fiber laser and phase sensitive optical time domain reflectometry, disturbances were monitored in long (several km) lengths of optical fiber. Narrow linewidth and low frequency drift in the laser were achieved through a combination of optical feedback and insulation of the laser cavity against environmental effects. The frequency drift of the laser, characterized using an all-fiber Mach Zehnder interferometer, was found to be less than 1 MHz/min, as required for operation of the intrusion detection system. Intrusions were simulated in a laboratory setting using a piezoelectric transducer to produce a controllable optical phase shift at the 2 km point of a 12 km path length. Interrogation of the distributed sensor was accomplished by repetitively gating light pulses from the stable laser into the sensing fiber. By monitoring the Rayleigh backscattered light with a photodetector and comparing traces with and without an induced phase shift, the phase disturbances were detected and located. Once the feasibility of such a sensor was proven in the laboratory, the experimental set up was transferred to Texas A&M's Riverside Campus. At the test site, approximately 40 meters of fiber optic cable were buried in a triangle perimeter and then spliced into the 12 km path length which was housed inside the test facility. Field tests were conducted producing results comparable to those found in the laboratory. Intrusions over this buried fiber were detectable on the ?-OTDR trace and could be localized to the intrusion point. This type of sensor has the potential benefits of heightened sensitivity, covertness, and greatly reduced cost over the conventional seismic, acoustic, infrared, magnetic, and fiber optic sensors for monitoring long (multi-km) perimeters.Item Orthopedic Correction of Growing Retrognathic Hyperdivergent Patients(2014-05-13) Carrillo, RobertoThe purpose of this prospective study was to determine whether dental intrusion is effective in treating growing retrognathic hyperdivergent patients without negatively affecting the roots and periodontal structures. The sample consisted of 17 (7 males and 10 females) consecutively treated patients who were 13.2 ?1.1 years old at the start of treatment (T1) and treated for 25.3 ? 9.3 months (T2). The maxillary posterior teeth (premolars and molars) were all intruded using a rigid segmental appliance. Two maxillary and two mandibular MSIs (immediately loaded with 150gr coil springs) were used for the intrusion mechanics and vertical control. A matched control group was used to evaluate the skeletal changes that occurred during treatment. CBCT records, taken at T1 and at the end of the orthopedic phase (T2) were used to evaluate the treatment effects. The results showed significant (p<.05) intrusion (2.5 ? 1.7 mm) of the maxillary dentition in the treated group. The mandibular plane angle closed 2? ?1.7? and the SNB angle increased 1.5? ?1.5?. True forward rotation of the treated sample was significantly (p<.05) greater (1.8?) than in the controls. The treated group showed greater superior and less posterior condylar growth than the controls, but the difference was not statistically significant. All of the maxillary roots showed statistically significant amounts of external apical root resorption (EARR), ranging from 0.67 mm to 1.21 mm. Pointed roots showed the greatest amounts of resorption, followed by bent roots, normal shaped roots, and roots with open apices, which showed the least EARR. Alveolar crest heights between first molar and second premolar decreased significantly (0.38 ? 0.6 mm) over time, and the distance between the bone and the CEJ increased significantly (0.52 ? 0.9 mm) only on the distal aspect of the maxillary second premolar. The overall MSI failure rate was 4.6%. It can be concluded that segmental intrusion of the posterior teeth with light forces and skeletal anchorage is effective for treating growing retrognathic hyperdivergent patients. The mechanics produced a significant true forward mandibular rotation, with minimal loss of crestal bone height and clinically acceptable EARR of the teeth that were intruded.