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20th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 01 Apr 2007 - 05 Apr 2007
- Location: Denver, Colorado, USA
- Published: 01 April 2007
1 - 20 of 164 results
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Post-Tsunami Helicopter-Borne Electromagnetics Along The Coasts Of Aceh, Indonesia
Authors B. Siemon, A. Steuer, U. Meyer and H.J. RehliAfter the earthquake and the tsunamievent on December 26, 2004, the Indonesian and German governments decided to set up a project that was dedicated to reinstall the public life of the people in the coastal region of Aceh Province, Indonesia. As the tsunami waves caused large scale coastal saltwater intrusions and destroyed thousands of shallow drinking water wells, the focal point was the water assessment in coastal areas of Aceh about nine months after the tsunami. The target areas are: Banda Aceh / Aceh Besar, the west coast between the towns of Calang (Aceh Jaya) and Meulaboh (Aceh Barat), and Sigli on the northeast coast. A helicopterborne survey including fivefrequency electromagnetics (HEM), magnetics and gammaray
spectrometry was conducted by the BGR airborne group from August to October 2005. The northernmost survey area, Banda Aceh / Aceh Besar, comprises a 20 km by 50 km wide area that was surveyed within four weeks. The HEM survey revealed coastal saltwater occurrences caused by the tsunami, deep saltwater occurrences up to several kilometres inland, and several potential freshwater occurrences. Several requests for information on the geological/hydrogeological situation at sites for planned water wells were successfully evaluated.
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Case Study Of A Rapid Response Underwater Search For A Tow Missile
More LessIn Mid July 2006 the USAESCH began searching for a prototype TOW missile using underwater EM61 and magnetometer sensors. The missile was lost in Indian Creek, on Redstone Arsenal in Alabama, and its flight motor was needed to analyze telemetry data. More than three weeks of searching with analog detectors proved fruitless. Believing digital mapping techniques would be easy, we quickly learned that variable current, confined operating areas and bottom obstructions will wreak havoc on the best of plans. Even anomaly marking and recovery proved a challenge in current and zero visibility. Urgency required rapid prototyping of a submersible housing for the EM61 sensor and our initial design placed the coil 0.3m below the water surface while allowing survey speeds of up to three knots. Four conventional missiles and assorted debris were detected using this configuration in shallow waters. In deeper areas we ballasted the housing for bottom-towing but repeated entanglement in sunken trees necessitated a new approach. A dual-sensor magnetometer array was towed at a constant depth of one meter in waters up to 3.5 meters deep and anomalies as small as one-gallon welding rod containers were found. The prototype missile was recovered in early August.
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Integrated Geophysical Investigation For The Vulnerability Assessment Of Earthen Levee
More LessIntegrated geophysical investigation was undertaken to assess the vulnerability of earthen levees to flooding and earthquake. The tested geophysical methods involved multi-channel surface wave dispersion measurement (MASW), capacitively coupled (CC) resistivity measurement, multi-frequency electromagnetic (EM) survey, and high-resolution seismic reflection survey using S-wave type Land Streamer. Because these methods required no fixing of sensors on the levee surface, high performance on field measurement work could be accomplished. The CC resistivity as well as EM survey successfully reconstructed resistivity profiles along levees, and delineated anomalously high or low resistivity zones within or beneath the levee body. The MASW method mapped shear wave velocity structures along levees, and clearly imaged relatively high or low velocity zones in the levee body. High-resolution seismic reflection surveying delineated the layered structure in the levee and in the underlying foundation sediments. Integrated investigations of resistivity and shear wave velocity structure remarkably highlighted the potentially permeable zones in the levee body as high resistivities and intermediate to low S-wave velocity areas. As a result, the geophysical methods effectively delineated the unexpectedly heterogeneous structure in the body of the levee, and the comprehensive investigation approach is shown to be helpful for the vulnerability assessment of levees through interpreting geophysical anomaly identified by means of integrated surveying.
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Analysis Of Naturally Occurring False Alarms At A Uxo Test Site On Jefferson Proving Ground
More LessThe detection and discrimination of UXO can be limited by small scale geologic anomalies that exhibit similar responses, both in spatial extent and amplitude, to real ordnance. These anomalies are referred to as naturally occurring false alarms (NOFA). During the Jefferson Proving Ground 4 (JPG4) demonstrations in 1996, a number of NOFA were identified in total field magnetic data with one being quite large. To explain the causes of these NOFA, in-situ magnetic susceptibility measurements were made over the anomalies as well as the collection of soil samples up to a meter deep. The soil samples have been analyzed for mineralogy and the magnetic susceptibility, as well as frequency dependence of susceptibility, have been measured in the laboratory. A number of the NOFA also exhibited reversed polarity which would mean that they probably quite shallow anomalies. A number of these NOFA have been modeled to determine their remnance. The results of all of these analyses lead to the conclusion that the large magnetic anomaly is due to mineral transport and deposition along two converging ephemeral streams.
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Electromagnetic Induction (Emi) Coil Sensitivity Maps For Evaluating Coil Designs And Configurations Used In The Geophysical Detection Of Unexploded Ordnance (Uxo)
Authors Neha Jain, Dr. Lloyd S. Riggs and Bob SelfridgeThis paper summarizes efforts to develop and test a software tool for evaluating electromagnetic transmitter coil designs and configurations used in the geophysical detection of unexploded ordnance (UXO). In particular, we are interested in evaluating the detection and discrimination potential of Wide-Area Transmitter and Multi-Transmitter (WAT-MT) sensor systems. The effort is directed toward developing a better understanding of the capabilities and limitations of WAT-MT sensor systems. A Matlab computer code has been developed that maps sensor response to a standardized infinitesimal object in a static field. These plots take in full account of both the transmitter and receiver coil shapes with no explicit consideration of target characteristics. The software allows the user to obtain sensitivity as well as streamline plots. Streamline plots are preferred over sensitivity plots when one is interested in visualizing the direction of the magnetic field due to the transmitter and/or receiver coil. A combination of streamline and sensitivity plots provides good insights into the overall capabilities of a particular coil configuration and also allows one to objectively compare competing designs. Measurements with the Geonics Ltd EM-61 and EM-63 will be compared with sensitivity plots in order to validate the WAT-MT software tool.
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Emi Detection And Discrimination Of Uxo Using An Array Of Fluxgate Magnetic Sensors
Authors Michael W. Asten and Andrew C. DuncanWhile existing technologies have proved successful in establishing the location of metal objects and scrap, additional measurements are required in order to discriminate shape and size of targets. The advantages of a fluxgate magnetometer as the sensor in EMI metal detection are established in a series of observed profiles over dummy UXOs, and a related set of modeling studies. A series of model studies was conducted to establish what improvement in target orientation information could be achieved with single or multiple vector fluxgate sensors compared with commercial conventional single-component single-sensor systems. The model studies use a novel fast approximation for a permeable prism which is capable of modeling the non-linear or frequencydependent magnetic properties of steel objects. The model studies show that when the target size is known, the use of a single vector sensor delivers an order of magnitude greater accuracy in location in 3D space and orientation of the target, compared with the use of vertical-component only data in conventional metal detectors. When the target size is unknown, a single vector sensor can produce accurate location, but is likely to produce unstable orientation estimates. We conclude that an array of receiver sensors is preferable. Comparison of a single vector sensor versus an array of three vector sensors in model studies shows that the array of three vector sensors has the advantage of delivering accurate and stable estimates of both location and orientation of the target, even when target dimensions are unknown.
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Berkeley Uxo Discriminator (Bud)
Authors Erika Gasperikova, J. Torquil Smith, H. Frank Morrison and Alex BeckerThe Berkeley UXO Discriminator (BUD) is an optimally designed active electromagnetic system that not only detects but also characterizes UXO. The system incorporates three orthogonal transmitters and eight pairs of differenced receivers. It has two modes of operation: (1) search mode, in which BUD moves along a profile and exclusively detects targets in its vicinity, providing target depth and horizontal location, and (2) discrimination mode, in which BUD, stationary above a target, from a single position, determines three discriminating polarizability responses together with the object location and orientation. The performance of the system is governed by a target size-depth curve. Maximum detection depth is 1.5 m. While UXO objects have a single major polarizability coincident with the long axis of the object and two equal transverse polarizabilities, scrap metal has three different principal polarizabilities. Our results clearly show that there are very clear distinctions between symmetric intact UXO and irregular scrap metal, and that BUD can resolve the intrinsic polarizabilities of the target. The field survey at the Yuma Proving Ground in Arizona showed excellent results within the predicted sizedepth range.
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Applications Of A Robotic Multi-Sensor Uxo Detection Platform
More LessTo reduce the cost of site characterization and cleanup, it is critical to implement new technologies capable of improved detection and discrimination of Unexploded Ordnance (UXO). Digital geophysical mapping and improved physics-based discrimination have led to reduced false alarm rates. Despite these improvements, current UXO technologies still have difficulty finding small UXO that are approximately the same size as most clutter objects, and challenges remain in adequately discriminating objects during a single detection/discrimination pass. In this study, we present the results of testing a multi-sensor Electromagnetic Induction (EMI) and Ground Penetrating Radar (GPR) array system originally developed for landmine detection. Our current advanced ordnance detection system integrates sensor arrays, highly accurate global and local positioning, and on-board target detection/classification software on the front loader of a semi-autonomous robotic platform. We focus on the analysis of features from two-dimensional EMI array data collected in a controlled test pit as well as multi-sensor EMI and GPR data collected during field tests on a range. High resolution steppedfrequency synthetic aperture GPR data yield images of small UXO and supporting information for discrimination against small clutter objects. Experiments with new EMI coil configurations and timedomain processing indicate potential for enhanced discrimination.
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Trend Removal And Detection Of Overlapping Magnetic Field Anomalies By Wavelet Analysis
Total magnetic field data measured for geophysical exploration purposes comprise the superposition of the effects of all underground magnetic sources. Usually the targets in magnetic
exploration are small, shallow buried bodies, and their magnetic field is superimposed on the regional field that arises from larger and/or deeper source or sources located further away. Sometimes inaccurately removed core fields or large scale topographic features also give rise to regional components. The regional field is generally smooth, adding a trend to the data. The estimation and subtraction of this trend field yields the residual field that corresponds to the target sources. Evidently, the reliability of the interpretation of the residual field depends on the correct estimation of the regional field. In this work the regional-residual separation in the wavelet domain is performed with the aid of the discrete wavelet transformation (DWT) realized with the use of compactly supported wavelets (Daubechies, 1990) with two or three vanishing moments. These wavelets are orthogonal to first or second order polynomials. This means essentially that the regional field (usually represented by a first or second order polynomial) is invisible to the wavelets and thus the regional field is almost entirely hidden in the coefficients of the coarser level of the wavelet transformation. However, in the realization of the DWT as decimated and periodized, the periodic assumption produces some non-zero contribution in a few detail coefficients. Therefore the suppression of all detail coefficients degrades the calculated regional field. To avoid such a distortion we can process a relatively large symmetrical extension of the
data sequence from both sides. Alternatively, we can use an internal model for the polynomial field that controls the separation. Because of the spectral overlap, the approximation of the regional field contains some of the energy of the residual field. We can tackle this problem by analyzing the reconstructed approximation of the regional field in a proper new wavelet basis (with the same number of vanishing moments) and repeating the separation procedure. The choice of the model is empirical; thus it depends on the interpreter’s experience. The wavelet that concentrates the energy of the regional field in the low-resolution coefficients and spreads the energy of the residual field in the high-resolution coefficients gives best results. A good choice of
wavelet pairs for the first order model is the Db4 and the triangular biorthogonal wavelet. For the second order model, the combination of the Db6 and Villasenor2 wavelets gives a very good separation. The proposed method preserves the signal’s features and has the ability to detect the possible local variations of the regional field. The same method can be used for the detection of overlapping magnetic field anomalies. Although the method may have application in more general settings we are mostly focused on archaeological geophysics, a fact that limits the kind of regional-residual problems which occur in certain ways.
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Ground-Penetrating Radar For Urban Archaeological Mapping
More LessUrban settings, which are one of the most challenging areas for archaeological near-surface geophysical mapping, can benefit from the use of ground-penetrating radar. The GPR method has the ability to focus energy downward and therefore can potentially map buried features within the clutter of pipes, trenches and other typical urban materials. In addition, GPR can map buried stratigraphy in three-dimensions, which allows stratigraphic analysis of buried deposits. When amplitude slice-maps are produced in various horizontal levels in the ground they can show changes in land usage by building period, making GPR maps analogous to excavation levels over many depths used in traditional archaeological excavations.
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Geophysical Investigation To Locate Buried Structures At The Site Of An 18Th Century House
Authors Jutta Hager, Joshua King and Robert A.S. BullerIn 2005 Hager GeoScience, Inc. (HGI) conducted a geophysical investigation at the site of a 1703 house outside Boston, Massachusetts. The structure, one of the oldest surviving First Period
houses in the United States, is located on a ¾-acre former colonial farm property that reportedly included several outbuildings, including at least one timber-framed barn. HGI performed the
investigation using a GSSI GEM-300 multifrequency terrain conductivity profiler and SIR-3000 GPR system with 400-MHz antenna. The survey located a primary target near the reported location of a former timber-framed barn, as well as a less well-defined target elsewhere on the site. Excavation of the primary target revealed an unmortared fieldstone foundation wall and a trash pit extending from just below the ground surface to the cemented till floor of the structure. The less well-defined target proved to be a natural feature consisting of bouldery till beneath outwash sands and gravels.
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Summary Of New Developments In Tdr For Soils
Authors Vincent P. Drnevich and Robert L. NowackTime Domain Reflectometry (TDR) is a method to determine the electromagnetic properties of soils and recent research indicates that TDR is an increasingly powerful tool to assess the engineering properties of soils. There were symposia and workshops on this topic held in 1994 and 2001 at Northwestern University and one in September 2006 at Purdue University. The authors were among the organizers of TDR 2006: 3rd International Symposium and Workshop on Time Domain Reflectometry for Innovative Soils Applications (TDR 2006) at Purdue University on September 17-20, 2006. There were five keynote presentations and thirty-five paper presentations with much discussion among the more than 70 researchers and practitioners from agricultural engineering, agronomy, electrical engineering, geotechnical engineering, soil science, and soil physics. The five themes were: 1) TDR Calibration in Challenging Media, 2) Geotechnical Applications of TDR, 3) Innovations, Challenges, and Future Opportunities, 4) TDR Probe Design and Selection, and 5) Hydrologic Applications of TDR. Papers to TDR 2006 are available free of charge on line at https://engineering.purdue.edu/TDR. This paper presents highlights of some interesting papers to TDR 2006. Items to be discussed include: effects of geometrical and interfacial factors on effective permittivity, improved methods for volumetric water contents for pavement bases and subgrades, cone penetrometers to measure permittivity and conductivity, a new TDR source signal that is non dispersive, and soil texture characterization from TDR waveforms. Unfortunately only a few of the many excellent papers could be highlighted. The paper concludes with a quotation from the presentation of G. Clarke Topp, the acknowledged father of modern TDR for soil moisture measurement.
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Geophysical Location, Identification, And Characterization Of Archaeological Structures Of The Jornada Mogollon People At The Three Rivers National Petroglyph, New Mexico
Authors Jaime O. Hincapié and Diane I. DoserWe present preliminary results of an ongoing study regarding the application of shallow geophysical methods to archeological sites using a unique combination of geophysical techniques. This approach adds precision, greater spatial resolution, and time efficiency. In 1976 a group of archaeologists discovered and reconstructed prehistoric structures at the Three Rivers National Petroglyph Site, New Mexico. The area is covered by dense vegetation and, moreover, it is often occupied by cattle and tunnel-digging, den-building mammals, which destroy both surface and subsurface features that could indicate centers of past human activity. The 1976 excavations successfully made use of magnetometry to help locate structures of interest. In the 30 years that
followed no further geophysical investigations were conducted, although periodic mapping of surface features and excavations continued. Between December 2005 and December 2006, a new set of geophysical campaigns were carried out at the site, in order to locate new structures. The surveys included ground conductivity, magnetometry (including gradiometry), and ground penetrating radar (GPR). We first used conductivity and magnetic gradiometry to delineate anomalies that could represent structures, followed by GPR. As of October 2006, three areas have been targeted as suspicious, and one of them represents an adobe structure that is currently being excavated. Further reconnaissance studies were carried out throughout December 2006.
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Gpr Survey Of The Japanese Imperial Family Tombs In Miyazaki: Application Of Gpr Overlay Analysis
Authors Dean Goodman, Hongo Hiromichi, Noriaki Higashi and Yasushi NishimuraA method is developed to create comprehensive 2D images of subsurface structures which are not level buried in the ground. The method, referred to as overlay analysis, uses desired portions of a complete time slice dataset where the relative-strongestreflectors are synthesized into single 2D images. The method is advantageous over simple thick slices since individual time slice components can be weighted independently in the compositing process. Successful implementation of overlay analysis is shown for the discovery of a destroyed 5th century burial moats surrounding the Japanese Imperial Family Burial Tombs in Kyushu.
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Grade Estimation At Cvrd Inco’S Canadian Sulphide Mines
Authors Glenn M. McDowell, Andrew D. Mackie and Mark PalkovitsThe paper provides an overview of grade estimation at CVRD Inco Limited’s (CVRD Inco) Canadian sulphide mines. The main Ni grade estimation technique used is blasthole conductivity. This
technique is applicable in zones where the sulphide is sufficiently well connected to provide eddy current responses in inductive conductivity probes. In zones where the sulphide content is low (less than 25-30%) and the degree of sulphide connectivity is insufficient to cause reliable eddy current responses in inductive conductivity probes, magnetic susceptibility is being employed to enhance Ni grade estimation. In these zones, magnetic susceptibility complements conductivity-based grade estimation
because of the monoclinic or magnetic pyrrhotite content of the sulphide. Additional techniques being investigated for grade estimation and discrimination between chalcopyrite-rich and pyrrhotite-rich mineralization include resistivity, natural gamma and density. The paper concludes with a summary of the nuclear-based PGNA (Prompt Gamma Neutron Activation) technique. This is a more direct grade determination technique that employs a neutron generator and gamma detectors. The resulting gamma ray spectra contain information about elemental concentrations including Ni, Cu, Co, Fe, S, Si, Ca, Al, etc.
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Groundwater And Environmental Applications Of Advanced Geophysical Logging Tools: Geochemical And Magnetic Resonance Tool Reviews
Authors Ned Clayton and Wendy WempeHigh-quality data and highly-skilled technical analysis are the keys to good decision-making about groundwater resource management and environmental site assessment issues. Typical water well geophysical logs are used qualitatively in the groundwater industry to identify potential changes in lithology and/or water quality. Advanced logging technologies, on the other hand, are used quantitatively to constrain aquifer properties, define aquifer heterogeneity, and determine water quality, leading to improved aquifer characterization, more accurate flow modeling, and more reliable fluid transport modeling. Two advanced logging technologies are particularly valuable to the groundwater and environmental industries: (1) electronic pulsed neutron geochemical logs and (2) nuclear magnetic resonance logs. This paper introduces the physical principles of these two advanced logging technologies and their respective applications.
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Borehole Logging As An Aid In The Design Of A Subsurface Pump Station
Authors Mario Carnevale and Jutta HagerThe Combined Sewer Overflow (CSO) Project in Providence, RI consists of a 16,000-foot-long TBM rock tunnel connecting to an 117x61x68-foot pump cavern 300 feet in the sedimentary rocks of the Providence Formation. An important consideration related to the pump cavern construction was the presence and potential angle of intersection of the pump cavern ceiling and/or walls with a highly deformed and friable graphitic shale unit, since this could have major impacts on worker safety and, therefore, the amount of structural support required. To gain a better understanding of bedrock conditions and discontinuities at the pump cavern location, the Project drilled and cored two deep rock boreholes for acoustic televiewer and caliper logging.
Data from the borehole logging were correlated with core descriptions in order to characterize the orientations and stratigraphic positions of discontinuities in the proposed pump cavern ocation. Based on the results of these analyses, the pump cavern was moved from its original proposed location.
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Cross-Borehole Flow Tests And Insights Into Hydraulic Connections In Fractured Mudstone And Sandstone
More LessCross-borehole flow tests provided insights into hydraulic connections in fractured and dipping mudstone and sandstone that were consistent with the lithostratigraphic and structural framework of a VOC-contaminated bedrock research site in west-central New Jersey. Two cross-borehole flow tests were completed. Each test involved measurement and analysis of transient flow in a newly installed deep corehole with a long open interval during short-term pumping and recovery in an adjacent shallow well with a short open interval. The cross-borehole flow test in the mudstone identified a hydraulic connection through a dipping fractured bed between the pumped interval in the well and a flow zone at an intermediate depth in the corehole. The presence of a hydraulic connection between the pumped well and the corehole was not obvious because the water-level response in the corehole was dominated by a shallow zone of high transmissivity, which was hydraulically isolated from the pumped interval. In the sandstone, the cross-borehole flow test identified a hydraulic connection along dipping fractured beds as well as a connection to a deep high-angle fracture that cuts across bedding. These results suggest that application of cross-borehole flow tests at other contaminated fractured-bedrock sites could provide insights into hydraulic connections useful the design and implementation of monitoring and remediation programs.
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Systematic Errors In Resistivity Measurement Systems
Authors Douglas La Brecque, William Daily and Paula AdkinsThe greatest obstacles in achieving higher resolution of electrical resistivity tomography (ERT) data are systematic errors that result from the non-ideal nature of measurement systems or
procedures. Systematic errors are correlated to the system functions and cannot be removed by data averaging. This paper discusses a number of sources of systematic errors including:
Errors in the system gains or calibration of voltage and current monitors, Leakage and coupling in multiplexers, cables and wires, and Electrode aging and impedance effects. Of particular concern are leakage currents within the types of cable used on sites in the past. These errors were found to be larger than expected. It is also important to investigate errors related to the electrodes used in ERT in part since errors such as the cable leakage depend partly on electrode impedance and in part as errors arise from the electrode themselves. There is no simple, clear relation between electrode errors and such factors as material type, history of use, and waveform time/frequency. Preliminary results indicated that the best electrodes were copper-copper sulfate even when they are used as both transmitters and receivers. The best, simple metal electrodes were welding steel.
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Efficient 2.5D Resistivity Modelling Using A Quadtree Discretization
Authors Robert A. Eso and Douglas W. OldenburgWe explore methods for improving the numerical efficiency to solutions of the 2.5D resistivity forward problem. By employing a quadtree structured mesh discretization, fewer model cells are
required in the solution and the volume of interest is easily extended so that zero-flux boundary conditions are satisfied. When these alterations are combined with matrix factorization methods we generate a computationally expedient solution to the 2.5D DC resistivity forward problem. A fast and accurate forward modelling forms the foundation of an inversion. Here we illustrate this by carrying out an inversion on a simulated data set.
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