Browsing by Subject "variability"
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Item An Investigation of the Optimal Sample Size, Relationship between Existing Tests and Performance, and New Recommended Specifications for Flexible Base Courses in Texas(2013-04-22) Hewes, BaileyThe purpose of this study was to improve flexible base course performance within the state of Texas while reducing TxDOT?s testing burden. The focus of this study was to revise the current specification with the intent of providing a ?performance related? specification while optimizing sample sizes and testing frequencies based on material variability. A literature review yielded information on base course variability within and outside the state of Texas, and on what tests other states, and Canada, are currently using to characterize flexible base performance. A sampling and testing program was conducted at Texas A&M University to define current variability information, and to conduct performance related tests including resilient modulus and permanent deformation. In addition to these data being more current, they are more representative of short-term variability than data obtained from the literature. This ?short-term? variability is considered more realistic for what typically occurs during construction operations. A statistical sensitivity analysis (based on the 80th percentile standard deviation) of these data was conducted to determine minimum sample sizes for contractors to qualify for the proposed quality monitoring program (QMP). The required sample sizes for contractors to qualify for the QMP are 20 for gradation, compressive strength, and moisture-density tests, 15 for Atterberg Limits, and 10 for Web Ball Mill. These sample sizes are based on a minimum 25,000 ton stockpile, or ?lot?. After qualifying for the program, if contractors can prove their variability is better than the 80th percentile, they can reduce their testing frequencies. The sample size for TxDOT?s verification testing is 5 samples per lot and will remain at that number regardless of reduced variability. Once qualified for the QMP, a contractor may continue to send material to TxDOT projects until a failing sample disqualifies the contractor from the program. TxDOT does not currently require washed gradations for flexible base. Dry and washed sieve analyses were performed during this study to investigate the need for washed gradations. Statistical comparisons of these data yielded strong evidence that TxDOT should always use a washed method. Significant differences between the washed and dry method were determined for the percentage of material passing the No. 40 and No. 200 sieves. Since TxDOT already specifies limits on the fraction of material passing the No. 40 sieve, and since this study yielded evidence of that size fraction having a relationship with resilient modulus (performance), it would be beneficial to use a washed sieve analysis and therefore obtain a more accurate reading for that specification. Furthermore, it is suggested the TxDOT requires contractors to have ?target? test values, and to place 90 percent within limits (90PWL) bands around those target values to control material variability.Item Improvement of Cotton Fiber Maturity and Assessment of Intra-Plant Fiber Variability(2012-10-19) Kothari, NehaThe temporal system of fruiting on the cotton plant lends itself to bolls at different fruiting sites developing under different environmental conditions and with varied source-sink relationships. To investigate this, intra-plant fiber quality was assessed in four upland cultivars at College Station, Texas for three years and at Lubbock, Texas for two years. It was concluded that fiber quality steadily declines from the bottom sympodial branches towards the upper branches. 'FiberMax 832' had the best fiber quality among all cultivars but it also had the highest degree of variability within the plants. 'Half and Half' and 'Acala 1517-99' appear to have the least amount of intra-plant variability of fiber quality. Bolls from the bottom region of the plant have higher trash content compared to the upper region. To test the impact of fiber quality variability on boll sampling techniques employed, ten sampling protocols were compared against each other for three years in College Station, Texas, for two upland cultivars. Results suggest that randomized boll samples containing 50 bolls worked well to estimate inherent fiber quality for most fiber traits while estimation of trash and lint percent was not predictable based on boll samples. One of the problems associated with intra-plant fiber variability was the presence of immature fibers. In order to determine the potential for improvement of fiber maturity and standard fineness, five upland cotton (Gossypium hirsutum L.) genotypes were subjected to a diallel analysis at College Station, Texas, in 2011. Four cultivars that tend to produce fine and mature fibers and one cultivar that tends to produce coarse fibers were intermated in all combinations, without reciprocals. Estimates of general (GCA) and specific combining ability (SCA) for fiber maturity ratio and standard fineness based on Griffing's diallel Model I, Method 4 were calculated for AFIS and fiber micronaire, length and strength measurements for High Volume Instrument (HVI). Four parents had significant GCA effects and Acala 1517-99 was found to be the best parent for improving standard fineness followed by FiberMax 832 and 'Tamcot HQ-95'. Tamcot HQ-95 was the best parent to improve fiber maturity ratio while 'Deltapine 90' was the best parent to reduce fiber maturity ratio. The specific cross between Acala 1517-99 and Tamcot HQ-95 had the best performance. Diallel analysis indicated that fiber maturity ratio was influenced by non-additive gene effects more than additive gene effects while fiber standard fineness was highly influenced by additive gene effects. Developing cultivars with optimal fiber standard fineness and maturity should be prioritized to address problems associated with neps and short fiber content and improve spinning performance of US cotton.Item Seasonal and Regional Variability of Stratospheric Dehydration(2012-07-16) Christenberry, Aaron JosephWe analyze output from a domain-filling forward trajectory model in order to better understand the annual cycle of water vapor entering the stratosphere. To do this, we determine the minimum water vapor saturation mixing ratio along each trajectory (the final dehydration point or FDP) and assume that the parcel carries that much water vapor into the stratosphere. In the annual average, the tropical Western Pacific, equatorial Africa and South America, and Southeast Asia are found to be the locations of the most frequent FDPs. Looking at individual seasons, we find that FDPs in the tropical western Pacific tend to occur in the summer hemisphere, with FDPs over South America and Africa occurring predominantly during the boreal winter. During boreal summer, a dehydration maximum occurs in the Asian monsoon region. In the annual average, FDP maxima occur at 99 and 84 hPa. Looking at individual seasons, we find that FDPs occur at higher altitudes (centered at 84 hPa) during boreal winter and at lower altitudes (99 hPa) during boreal summer. The annual cycle in FDP altitude combines with the annual cycle in tropical tropopause layer temperatures to generate the observed annual variations in water vapor entering the stratosphere.