Summary In recent years, the use of computerized tomography (CT) to characterize two-phase fluid flow through porous media has become increasingly popular. This paper describes a different application of CT: its use as a core analysis tool. The advantages and disadvantages of the different technological generations of commercial medical CT scanners available as core analysis instruments are also discussed. Additionally, methods are presented for improving images and reducing CT-number errors inherent in the scanning of high-density rock samples on instruments whose software was designed for the scanning of low-density human patients. Introduction CT, or computerized axial tomography or computer-assisted tomography (CAT) scanning, is a nondestructive X-ray technology that produces an image of the internal structure of a cross-sectional slice through an object by the reconstruction of a matrix of X-ray attenuation coefficients.1,2 The method is fast - 50 msec to 7 minutes per image, depending on the technological generation of the instrument - and requires little or no sample preparation. An imaged slice can be divided into an n×n matrix of voxels (volume elements). The attenuation of No X-ray photons passing through any single voxel having a linear attenuation coefficient µ reduces the number of transmitted photos to N according to Beer's law:N=No exp(-µx), Where x is the dimension of the voxel in the direction of the X-rays. Material parameters that determine the linear attenuation coefficient of a voxel include its density ? and mass attenuation coefficient µm:µ=µm?. Mass attenuation coefficient, in turn, depends on the atomic number of the material and the photon energy of the beam. For multicomponent voxels - i.e., mineral grains and porosity - the atomic-number dependence is weighted by the volume fraction of each component (partial volume effect). Thus the composition and density of the material in a voxel will determine its linear attenuation coefficient. A convention in medical imaging is to normalize the measured linear absorption coefficient to that of water:Equation By definition, air and water have CT numbers, NCT's, of -1000 and zero, respectively. In addition to conventional medical applications of CT, its use to characterize flow through porous media has become common in recent years.3–8 Other applications include coal,9 soil,10 and core11–13 analyses; core-sample/borehole-position correlation14; engineered-material quality-control analysis15,16; and geotomography, an extension of CT principles.17 Experimental All CT data were obtained on conventional medical scanners. Unless otherwise stated, the instrument was an unmodified, second-generation, dual-slice Technicare Deltascan 100 head scanner with a tungsten source, seven bismuth germanate detectors, and a DEC PDP 11/04 computer system. This unit operates at a tube voltage and current of 120 kV and 25 mA, respectively. For display, each voxel is assigned one of 64 gray levels on the basis of its CT number, with dark corresponding to a low CT number and bright corresponding to a high CT number. Quoted voxel size is 1×1×8.3 mm [0.4×0.04×0.3 in.]. To reduce beam-hardening effects, samples were surrounded with either sand or an aqueous potassium iodide solution, as noted in the applications. Beam hardening is a phenomenon that occurs at the air/sample interface and results in edge-brightening image artifacts that have falsely high CT numbers. In cases where a liquid medium was used to surround a porous sample, the sample was first coated with a low-attenuation, waterproof silicon gel. These media are not visible in the images because they have lower attenuation factors than the samples and do not appear at settings optimal for viewing the samples. All images and CT-number data were obtained directly from the system computer. Core Analysis Applications Applications presented and discussed here includevisualization of the extent of mud invasion;detection of fractures;lithologic characterization of cores encased in conventional opaque preservation material, rubber-sleeve core barrels, and stainless-steel pressure vessels;core screening before laboratory flow tests; andcorrelation of CT data to porosity, permeability, and mineralogy. Visualization of Mud Invasion. Visualization of the extent of mud invasion is illustrated in Fig. 1, a CT image through a slabbed, 8.9-cm [3.5-in.] -diameter homogeneous sandstone core. The sample was embedded in sand to reduce beam-hardening artifacts. Drilling mud has a high attenuation factor because of its high barite content. Consequently, its CT number is higher than that of sandstone. It can be seen that mud invasion (bright areas) occurred both at the core perimeter (bottom and left) and along a fracture near the top edge. In contrast, the dark areas in the interior represent rock not invaded by drilling mud. Knowledge that drilling mud is present aids in the calculation of accurate native oil and water saturations. Visualization of Mud Invasion. Visualization of the extent of mud invasion is illustrated in Fig. 1, a CT image through a slabbed, 8.9-cm [3.5-in.] -diameter homogeneous sandstone core. The sample was embedded in sand to reduce beam-hardening artifacts. Drilling mud has a high attenuation factor because of its high barite content. Consequently, its CT number is higher than that of sandstone. It can be seen that mud invasion (bright areas) occurred both at the core perimeter (bottom and left) and along a fracture near the top edge. In contrast, the dark areas in the interior represent rock not invaded by drilling mud. Knowledge that drilling mud is present aids in the calculation of accurate native oil and water saturations.
There remains a large gender imbalance in the science, technology, engineering and mathematics (STEM) workforce deriving from a leaky pipeline where women start losing interest and confidence in science and engineering as early as primary school. To address this disparity, the Science Research & Engineering Program (SREP) at Hathaway Brown School was established in 1998 to engage and expose their all-female high school students to STEM fields through an internship-like multi-year research experience at partnering institutions. We compare data from existing Hathaway Brown School SREP alumnae records from 1998–2018 (n = 495) to Non-SREP students and national datasets (National Center for Educational Statistics, National Science Foundation, and US Census data) to assess how SREP participation may influence persistence in the STEM pipeline and whether SREP alumnae attribute differences in these outcomes to the confidence and skill sets they learned from the SREP experience. The results reveal that women who participate in the SREP are more likely to pursue a major in a STEM field and continue on to a STEM occupation compared to non-SREP students, national female averages, and national subsets. Participants attribute their outcomes to an increase in confidence, establishment of technical and professional skills, and other traits strengthened through the SREP experience. These data suggest that implementing similar experiential programs for women in science and engineering at the high school stage could be a promising way to combat the remaining gender gap in STEM fields.
This study examines the types of clothing worn by African American women living in the state of Georgia between 1890 and 1914. The researchers used historical photographs as primary sources to document clothing. The photographs are located in three collections: Spelman College, Atlanta University, and the Georgia Department of Archives and History. The clothing in each photograph was recorded and compared to styles of clothing advertised in national magazines of the period corresponding to the date of the photograph. Analysis revealed that (a) African American women in Georgia in the late nineteenth and early twentieth centuries wore clothing similar in style to fashions advertised and illustrated in magazines and newspapers of the period, and (b) some items of dress were distinctive, that is, not illustrated in national periodicals of the time.
This paper discusses the value of newspaper notices in the search for data on slave clothing. Two hundred and seventy-three fugitive slave notices, 10 sheriff notices, and 79 store advertisements were examined from 34 Georgia newspapers published from 1800 to 1865. Although these sources provide us with, in most cases, extremely detailed information about slave clothing and textiles, researchers should also recognize the limitations these sources have. These include a narrow picturing of the slave runaway population (mostly male slaves) as seen in a relatively small number of extant newspapers that carry notices. If researchers keep these restrictions in mind when drawing conclusions based on these sources, extant newspapers of the times can reveal much about the slave clothing which is no longer available for research.
A low Earth orbital space experiment entitled, "Polymers Erosion And Contamination Experiment," (PEACE) has been designed as a GetAway Special (GAS Can) experiment to be accommodated as a Shuttle in-bay environmental exposure experiment. The first objective is to measure the atomic oxygen erosion yields of-40 different polymeric materials by mass loss and erosion measurements using atomic torce microscopy. The second objective is to evaluate the capability of identifying sources of silicone contamination through the use of a pin-hole contamination camera which utilizes environmental atomic oxygen to produce a contaminant source image on an optical substrate. 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION OF REPORT OF THIS PAGE
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