Horizontal unsaturated flow across a single fracture

Unsaturated flow in a silica rich rock is driven by two primary forces, gravity, which drives water downward, and capillarity, which acts in all directions. The balance between gravity and capillary forces determines fluid flow. Water in an unsaturated silica rich matrix will adhere to the silica particles and through capillary action spread out in all directions. Fractures under unsaturated conditions, will act as capillary barriers to horizontal capillary flow. This restriction is due to an interruption in the continuity of grains along which water adheres to in the rock matrix. Given adequate time and fluid pressure, water may bridge across the fracture to continue flow on the downstream side of the rock matrix. If the system reached saturation, the same fractures that inhibited flow will act to increase storage capacity, and transport water along the fracture network (Glass et al., 2003). This thesis investigated horizontal fluid flow by constructing a working model. This model consisted of a nearly homogenous and isotropic quartz rich sandstone slab enclosed in a clear glass case. In this experiment, water was delivered to the initially dry sandstone slab and allowed to saturate the matrix. In a second trial matrix continuity was interrupted through the introduction of a fracture into the sandstone slab. This single fracture acted as a barrier to unsaturated flow. Water advanced across the matrix in a horizontal direction until it made contact with the fracture and stopped. By allowing the upstream matrix to saturate, fluid pressure increased until water was able to form a meniscus bridging the fracture. Once the meniscus was in place the fracture could saturate where the aperture was narrow, allowing flow across the fracture to the downstream block. Fractures that were modified to contain fewer contact points and a wider aperture, resulted in significant delay of water advancement in the downstream block

Electronic transport properties of stabilized amorphous selenium x-ray photoconductors

Amorphous selenium (a-Se) and its alloys are important photoconductor materials used in direct conversion flat panel digital x-ray detectors. The performance of these detectors is determined, in part, by the electronic transport properties of the a-Se photoconductor layer – namely, the charge carrier mobility m and the deep trapping lifetime t. The product of the mobility and the lifetime mt, referred to as the charge carrier range, determines the average distance that photo-generated charge will travel before being removed from the transport band by deep localized states in the mobility gap of the semiconductor. The loss of carriers to these deep states reduces the amount of charge collected per unit of x-ray exposure, and, hence, limits the x-ray sensitivity of the detector. Two experimental techniques that may be used to measure the transport properties of holes and electrons in high resistivity semiconductors are described in this thesis. The Time-of-Flight (TOF) transient photoconductivity technique is used to evaluate the charge carrier mobility by measuring the time required for the charge carriers to transit a fixed distance under the influence of an applied electric field. The Interrupted-Field Time-of-Flight (IFTOF) technique is used to determine the charge carrier deep trapping time; the drift of the injected carriers is temporarily interrupted at a position in the sample by removing the applied field. When the field is reapplied the number of charge carriers has decreased due to trapping events. The carrier lifetime is determined from the dependence of the fraction of recovered charge carriers before and after the interruption with the interruption time. TOF and IFTOF measurements were carried out on a number of samples of vacuum deposited selenium alloy x-ray photoconductors. Device quality photoconductor films are fabricated by evaporating a-Se source material that has been alloyed with a small quantitiy of As (~0.3 at. %) and doped with a halogen (typically Cl) in the p.p.m. range. The dependence of the carrier range on the composition of the photoreceptor film was accurately measured using both TOF and IFTOF measurements. It was found that the transport properties of the film could be controlled by suitably adjusting the composition of the alloy. Combined IFTOF and TOF measurements were also performed on several samples to examine the effects of trapped electrons on the hole transport properties in a-Se films. It was found that drifting holes recombine with the trapped electrons, and that this process could be described by a Langevin recombination process. This finding is important for the correct modeling of amorphous selenium digital x-ray detector designs. Finally, the effects of x-ray exposure on a-Se films were examined. A temporary reduction in the effective hole lifetime was observed due to an increase in the number of hole capture centers following an x-ray exposure. The capture coefficient between free holes and the x-ray induced hole capture centers was measured using combined TOF and IFTOF measurements. It was shown that this capture process was governed by the Langevin recombination mechanism. From these observations it was concluded that trapped electrons from a previous x-ray exposure act as recombination centers for subsequently generated holes, thereby reducing the effective hole lifetime in the sample

Merrimack College: The First Fifty Years, 1947-1957

Merrimack College Fiftieth Anniversary Photo Book Text Editor: Robert (Bud) D. Koehan \u2753 Photograph Editor: Frank J. Leone Jr. \u2761https://scholarworks.merrimack.edu/mc_pubs/1004/thumbnail.jp

Wroclaw neutrino event generator

A neutrino event generator developed by the Wroclaw Neutrino Group is described. The physical models included in the generator are discussed and illustrated with the results of simulations. The considered processes are quasi-elastic scattering and pion production modelled by combining the $\Delta$ resonance excitation and deep inelastic scattering.Comment: Talk given at 2nd Scandanavian Neutrino Workshop (SNOW 2006), Stockholm, Sweden, 2-6 May 2006. 3 pages, 6 figure

Games in Agriculture, Food, and Natural Resources Education

Educational games provide learners with team-based, experiential, and problem-centered learning opportunities. Therefore, educational games are recommended to encourage learner success in an increasingly complex and collaborative world. Research exploring interventions to increase teacher affinity toward games is needed to inform expansion of games within classrooms. The current study leveraged the input, environment, and outcomes model to analyze perceptions of games held by school-based agriculture, food, and natural resources (AFNR) educators before and after a professional development experience focused on educational games. Results indicate teachers held a favorable perception of games before engaging in the professional development. Engagement in the professional development was related to only minimal increases in the perceptions held by teachers regarding educational games. Importantly, individual items within the construct illuminate an expanded view of educational games and their utility within AFNR classrooms as a result of the professional development experience. Specifically, respondents saw educational games as being valuable to engage learners in new content, not just as a review tool. Findings suggest a professional development experience related to games may help expand teacher conceptualizations of educational game utility. Specific recommendations are included to expand teacher understanding and use of educational games

Coastal resort development and impacts on shallow water aquifers in southern Baja California, Sur. Mexico

A Coastal resort named Fiesta Surf is being planned for the southern portion of the Baja peninsula on the Pacific coast between the resort town of Cabo San Lucas and Todos Santos. Two additional resorts and an exclusive housing community are in the planning stages within this region, known as the Pacific Corridor. The proposal for development is in a high growth region near the southern tip of the Baja peninsula in the state of Baja California, Sur, Mexico. The Pacific coast of southern Baja has seen little development and consists largely of non-developed shoreline. The current economic base of the area is ranching, small agriculture farms, and fishing. The Fiesta Surf Corporation plans to develop 500 acres as a coastal resort, golf course, and possible marina for recreation and tourism. Development of golf courses and resort hotels will have dramatic impacts on the water resources of the area. The extent of those resources, has had little attention with regards to indepth studies. The geology of Southern Baja is complex and has not been the issue of intense exzamination. Water resources are directly related to rock types, topography, drainage patterns, and geology with regards to structure. Alluvial deposits are especially important determinants of water yield from any aquifer. This paper examines the potential of surface and ground water resources to support the planned developments in Southern Baja