Underwater static targets are objects under the water that can¡¦t move autonomously. Apparatus feasible for detecting underwater static targets includes: optics, acoustics and geophysical instruments. The purpose of this research is discussing the efficiency of applying side-scan sonar, magnetometer, sub-bottom profiler and echo sounder simultaneously to search, detect, identify and locate underwater static targets. Procedures of this research include: 1. Discussing the capabilities of instruments and identification principles on target. 2. Using a real case to groundtruth target identification principles. 3. Assessing the superiority of the methodology. According to the characteristics of these apparatus, the water depth, collected by echo sounder, is capable of expressing the relief of the seabed. Seabed sonographs, recorded by side-scan sonar, show that it is feasible to detect, identify and locate targets on the seabed. Sub-bottom profiler provides the sub-surface sedimentary information which can be used to detect buried targets. Magnetometer can detect environmental magnetic intensities, which can locate and determine the size of ferrous targets. Analysis of the data collected at Hai-Köu Wan, Ping-Dong County yields following conclusions: 1. The water depth data, recorded per 15 meters by the echo sounder, is capable of detecting large targets and concentrated artificial reefs only. 2. Sonographs obtained by side-scan sonar show target¡¦s characteristics and location on seabed. It can be utilized to identifying targets and mapping targets distributions. 3. Sub-bottom profile graphs show the composition and thickness of sub-surface sediments. 4. Magnetic anomalies show that there are evident variations around the battle-ship reef or concentrated electric-pole reefs on the research area. It represents that the magnetometer is capable in detecting underwater ferrous targets. 5. Targets detecting rate and identifying accuracy can be increased by the mutual comparison of various information. By applying the technique established in this research and the survey results at Hai-Köu Wan, targets at the survey site can be identified and located precisely. There are about 1100 units of 2-m concrete reefs, 670 units of electric-pole reefs and a battle-ship reef at Hai-Köu Wan. It can be concluded that, applying echo-sounder, side-scan sonar system, sub-bottom profiler and magnetometer simultaneously can search, detect, identify and locate underwater static targets more effective than applying a single instrument such as side-scan sonar system.

Multi-beamecho sounder systemhas been around nowfor some 40 years and their use in shallow waters for the last 14 years. With modern shallow water systems running at up to 9,600 soundings/second, data collection at the rate of approximately 250 million soundings/day system is possible. Processing of Multibeam Echo sounder (MBES) data is a challenging task from both hydrographic and technological perspectives. We recognize that a completely automatic system is improbable, but propose that significant benefits can still be had if we can automatically process good quality data, and highlight areas that probably need further attention. We propose an algorithm that takes uncleaned MBES data and attempts to pick out outliers as possible as we can. The traditionalmethod that is still in use today by numerous software applications is based on a line-by-line processing approach. Automatically filtering for a depth window, by beam number, slope between points, quality flags and recently by whether the beam¡¦s error is outside the IHO order for the survey are a number of ways in which the line-by-line approach has been speeded up. The fundamental differences between our method and the previous methods are that our algorithm does not actually delete any soundings at all and transform original one dimension information into two dimensions. Finally, we use Hierarchical Clustering to classifyMBES data into outliers and normal. We develop the user interface formulti-beamecho sounder quality control. It provides almost the necessary tools and modules to perform a survey. Standard modules are Survey planning (track guidance lines, waypoints), channel design and 3D modeling, data acquisition, data QC and data processing/flagged. However, it will visualize the soundings to aid the decisionmaking process.

Nondestructive testing (NDT) plays a more important role today in evaluating structural integrity of civil infrastructure. Impact-echo method (IE) is an effective stress wave based NDT method for locating defects in concrete structures. However, the contact requirement between sensor and concrete surface significantly limits the test speed and wide application of this method to large-scale structures such as bridges. Recent studies show the feasibility of air-coupled sensing, which eliminates the contact requirement and thus accelerates IE test. To further improve the test speed, a fully non-contact IE test using air-coupled sensing and excitation is investigated in this dissertation. This dissertation provides the theoretical basis required for developing an effective air-coupled IE method. For air-coupled sensing, 2D numerical simulations are first conducted to study the wave propagation in the air-solid system during IE tests. Visualized wavefield indicates that parabolic reflectors can effectively enhance the IE signal strength by focusing airborne IE waves to an air-coupled sensor. To maximize signal amplification, an analytical solution for the focused axial pressure response of a parabolic reflector with incident plane waves is derived. This solution is used to determine the reflector geometry that gives the highest focusing gain. For air-coupled excitation, a focused spark source with an ellipsoidal reflector is employed to excite stress waves in concrete. Numerical simulations and available nonlinear computer code (KZKTexas) are employed to investigate the reflector geometry that gives the highest stress wave excitation in solids. An acoustical muffler that works with the focused spark source is proposed to decrease the spark-induced noise level. The effect of source receiver spacing on received IE signals is studied. Simulated wavefield demonstrates that the mode shape of IE surface displacement distribution along the radial direction matches the Bessel function of the first kind (J0). Numerical 3D simulation results show the relation between focused IE signals and source receiver spacings, and indicate the spacing should be minimized to obtain better focused IE signal strength. Air-coupled IE test using through transmission setup is also investigated. / text

Non-destructive testing (NDT) plays an important role today in condition assessment of civil infrastructure. Among these NDT methods, the Impact-Echo (IE) method is widely used to determine the thickness of a plate structure and locate delaminations in concrete. The conventional IE test uses a contact impact source and a contact sensor, which limits the scanning speed. Recent studies show the feasibility of applying the air-coupled sensing technology to the IE test. With the contact requirement eliminated, a fully air-coupled NDT system can be realized to achieve rapid scanning on large scale structures. In this dissertation, the air-coupled IE test is first simulated using 2D finite element models. The numerical simulation results are validated by experimental measurements. It is shown that the airborne IE mode is a quasi-plane wave in air. A parabolic reflector is proposed to focus the airborne IE wave and amplify the air-coupled IE test signals. The focusing effect is validated by experimental results. By applying a parabolic reflector to the air-coupled sensor, it is found that large sensor lift-off height and source-receiver spacing can be used in the air-coupled IE test. The geometry of the parabolic reflector and source-receiver spacing are optimized using numerical simulations. A focused spark source is proposed as a non-contact source for the fully air-coupled test system. The spark source is first calibrated in an anechoic chamber. The feasibility of using the focused spark source for stress wave excitation is validated by experiments. A fully air-coupled testing system is realized by combining the air-coupled sensor and the air-coupled source. Experimental studies show that this system can measure surface wave and the IE mode. The fully air-coupled system is tested using a conventional IE test setup and a through transmission test setup. An acoustic muffler is introduced to suppress the acoustic noise from the spark source. Several advanced signal processing techniques to reduce the acoustic noises are also investigated. The air-coupled sensor has been adopted on a crawler NDT system for concrete inspection in a noisy field environment. / text

In the age of the Internet, extreme groups have seen resurgence in the way they can communicate and recruit through the new medium whether they are white supremacists or hacktivists. Examining the history and modern behaviors of both white supremacy groups and Anonymous, this paper aims to research and answer how the different groups use the Internet to influence identities and if the methods to do so differ from the old ones and through the use of several concepts, mainly the Echo Chamber and the Filter Bubble, narrow down the effects that leads to a person joining an extreme group.

The abandonment of Heracles at the end of Book 1 in Apollonius Rhodius’ Argonautica marks a turning point for Jason and the rest of the Argonauts. The aid of their mightiest hero, upon whose strength they had relied, is lost to them and they must find a means of accomplishing their nearly impossible mission without him. Allusions to Heracles occur throughout Book 2, in all nine units of action, drawing the reader’s attention to Argonauts’ efforts to carry on in the face of their loss. These allusions can be grouped into four categories: explicit mention, verbal echo, extrapolative allusion, and geographic reference. The poet’s deliberate deployment of these allusions highlights the extent to which Heracles’ strength-based approach to problem solving still influences the Argonauts’ actions in Book 2. This approach contrasts with the role played by divine agents, which increases markedly in the poem’s second half, beginning with Book 3.

A primary goal of this thesis has been to demonstrate that stable, useful measurements of the orientation of the acoustic signal vector as a function of range and time can be obtained from ocean backscatter, and that this orientation, or acoustic phase, can be related to the local sound speed distribution. Such a measurement is quite distinct from the related problem of detecting the rate of phase change, which forms the basis of Doppler technology. Doppler measurements can be made using echoes from a single point, or a sparsely distributed set of targets. Consistent and useful measurement of absolute phase, is inherently more difficult, since it depends upon the positions of individual scatterers, which are normally random and sparse relative to the acoustic wavelength. / Graduate

Resistance spot welding is used frequently as a successful joining method for a variety of work commonly in automotive and other manufacturing processes. Spot weld nugget is generally hidden between two sheets, causing its inspection difficult and expensive. Undersized nuggets, brittle or cracked nuggets, and excessive indentation of electrodes reveals the lack of fusion between the parts that can make the weld sub-standard. Visual inspection, pry testing and physical teardown with chisel and hammer method or a combination of them are being used traditionally. However, this study presents a more effective nondestructive inspection method based upon an ultrasonic pulse-echo technique. The theory of the technique together with the experimental verification are presented and its advantages over the other destructive and nondestructive techniques are considered.

Thesis (Ph. D.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 29, 2007) Includes bibliographical references (p. 66-67).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1967. / Typescript. Vita. "Diel activity and vertical distribution of yellow perch ... under the ice," by Gary L. Hergenrader and Arthur D. Hasler inserted between leaves 15 and 16. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.