Pleistocene geology of the Comstock-Sebeka area, west-central Minnesota

This study is a reconnaissance of the surficial geology and a reconstruction of the late Cenozoic history of an area in westcentral Minnesota. The study area extends eastward from the Comstock area (14 miles south of Moorhead, Minnesota) in the Red River Valley to the Sebeka area (13 miles north of Wadena, Minnesota). The area is about 27 kilometres wide and 140 kilometres long. Surface materials include Pleistocene glacial sediment and Pleistocene and Holocene fluvial, lacustrine, eolian, and bog sediment. Four geomorphic districts are recognized. The flat Lake-Plain District is underlain by sand, silt, and clay that was deposited as offshore sediment in the Lake Agassiz basin in Early Holocene time. The flat to rolling Shoreline-Complex District is underlain largely by lacustrine shoreline sand and gravel. The district includes the complex network of beach ridges and wave-cut scarps that were developed at the margin of Lake Agassiz in Late Wisconsinan and Early Holocene time. The gently undulating to strongly rolling Glacial-Upland District is underlain by glacial and fluvial sediment that varies in age from pre-Wisconsinan to Late Wisconsinan. Topography characteristic of subglacial smoothing and the collapse of englacial.and superglacial debris, as well as meltwater channels, eskers, and esker complexes are characteristic types of morphology present in the district. The Outwash District is underlain largely by sand and gravel that was deposited by rivers that flowed on top of and from melting glacier ice. The characteristic morphology of the district includes collapsed outwash topography and pitted outwash plains. The deposits of four glacial events form four lithostratigraphic units-that are recognized at the surface in the study area. The units, which are characterized by distinctive texture and lithology of the very-coarse-sand fraction of the glacial pebble-loam, are readily recognized in the field by differences in color, structure, and texture. The pre-Wisconsinan or Early Wisconsinan Sebeka Formation, Early Wisconsinan New York Mills Formation, Late Wisconsinan Dunvilla Formation, and Late Wisconsinan Barnesville Formation were deposited by advances of glacial ice that came from the northeast, due north, northwest, and northwest respectively. All but the Barnesville Formation correlate with other lithostratigraphic units in northwestern Minnesota and northeastern North Dakota

Development of novel polymeric materials for gene therapy and pH-sensitive drug delivery: modeling, synthesis, characterization, and analysis

The aim of this work was to obtain a fundamental understanding of drug release mechanisms from polymers that undergo thermoreversible gelation and to synthesize new polymers based on these that exhibit both pH and temperature sensitivity. Novel block and random copolymers with cationic character have been developed for drug delivery and gene therapy applications. The development of these materials began with a study of the mechanism of drug release from poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) block copolymers. This study revealed the release rates of drugs from water-soluble hydrogels composed of the PEO-PPO-PEO block copolymer PluronicRTM F127 was dictated almost solely by the rate of interfacial dissolution at the water/gel interface. A setup was designed to measure drug release from such soluble systems in order to avoid confounding hydrodynamic effects as a result of shear on the delicate polymer/gel interface. This study was followed by a complementary analysis of the effect ionic salts play in the phase transitions and drug release profiles in aqueous F127 solutions.;In an attempt to incorporate pH sensitivity into such drug release systems, several block copolymers of poly(N,N-diethylaminoethyl methacrylate) (PDEAEM), PEO and PPO were synthesized via anionic polymerization. Diblock materials (PEO-b-PDEAEM), either with or without a carboxylic acid endcap, were synthesized and characterized. Tablet dissolution experiments demonstrated pH-sensitivity in their drug release profiles relative to PEO tablets. Pentablock materials (PDEAEM-b-PEO-b-PPO- b-PEO-b-PDEAEM) were synthesized that maintain the thermoreversible gelation and micellization properties of F127 while introducing pH-dependent release from aqueous gels of the copolymer. This is the first example of non-crosslinked materials that exhibit both pH- and temperature-sensitive behavior. Using a similar synthesis route, random copolymers of PDEAEM and poly(poly(ethylene glycol) methyl ether methacrylate)) (PEGME) were synthesized which are water soluble and non-cytotoxic, whereas homopolymers of PDEAEM are neither. These materials have potential as gene therapy vectors

Determining Potential Herbage Production in the Sahel

The study illustrates a method to estimate the distribution of potential herbage production over large areas of the African Sahel under varying climatic conditions. The exploration of the method began after consulting with Mr. Albert A. Klingebiel. As a result of the discussion the study is determined to be practicable based upon the following three points: 1) potential herbage production is not known for large areas of the Sahel; 2) the spatial distribution of potential, herbage production varies with differences in soil characteristics and in amount of precipitation; and 3) potential herbage production is known for the soil associations of an area of the Sahel in the Republic of The Sudan (informally The Sudan) receiving average annual precipitation. The study tests a procedure to estimate potential herbage production in an area of the Sahel where soils and precipitation regime are considered similar to The Sudan Sahel, but where no statistical data on range productivity are available. A basic assumption to the procedure is that analagous habitats will produce similar amounts of herbage. The method also is designed to estimate potential herbage production for above average and below average annual precipitation levels. A mathematical concept is employed to estimate potential herbage production which is above or below average. The applicability of the mathematical concept was confirmed by Dr. James Lewis. The method requires that remote sensing techniques be used to determine the characteristics and extent of the soil associations in the study area. Remotely sensed data derived from Landsat satellite multispectral imagery provide the user with environmental data over large areas. The large area coverage is the key to obtaining the information on which a small-scale estimate is based. The area chosen for study is the Sahelian Zone of the Islamic Republic of Mauritania. The Sahel of Mauritania was chosen because potential herbage production is not known for the area while soil association characteristics and precipitation data are known

NEOGENE DRAINAGE REVERSAL AND COLORADO PLATEAU UPLIFT IN THE SALT RIVER AREA

The modern Salt River flows southwest from the Colorado Plateau, through the Arizona Transition Zone and into to the Basin and Range. Rivers in this area flowed northeast during the Paleogene from the Laramide Mogollon Highlands into structural basins of the topographically lower southern Colorado Plateau area. One of these rivers carved the Salt River paleocanyon through a portion of the Mogollon Highlands known as the Apache Uplift to similar depths as the modern Grand Canyon. This study refines the timing of this drainage reversal in the Salt River area by constraining the ages of paleoriver sediments deposited during the time of northeast-flowing rivers, internal drainage and southwest-flowing rivers. These results provide insights into the evolution of the southern Colorado Plateau. U-Pb dating of detrital zircon is used for maximum depositional ages and provenance analyses. 40Ar/39Ar dating of detrital sanidine is used for higher precision maximum depositional ages. The majority of paleoriver samples that were analyzed with both detrital zircon and sanidine show similar maximum depositional ages. Minimum or direct depositional ages are determined by overlying or interbedded volcanic units. The Mogollon Rim Formation is composed of river gravel, sandstone and mudstone on the southern rim of the Colorado Plateau that were deposited by northeast-flowing rivers. Results indicate deposition began after 59.38 Ma in the Flying V Canyon area and from 37 – 33.55 Ma in the Trout Creek section. The Whitetail Conglomerate represents the transition from northeast-flowing rivers to internal drainage in the Salt River paleocanyon. Whitetail Conglomerate is as old as the interbedded 37.6 Ma dacite in Canyon Creek fault side drainages, but deposition in the axis of the Salt River paleocanyon occurred between 30 and 21.8 Ma. The transition from northeast-flowing rivers to internal drainage occurred between 33.55-30 Ma marking the age of initial development of the southern edge of the Colorado Plateau. Apache Leap tuff flowed NE down Salt River paleocanyon nearly to Canyon Creek fault at 18.6 Ma. Internal drainage is documented by the 14.67 Ma Black Mesa basalt that flowed onto underlying lake beds. The first southwest-flowing river system in the Salt River paleocanyon deposited the Dagger Canyon conglomerate after incising at least 200 m deep into the Whitetail Conglomerate. The lower Dagger Canyon conglomerate is present in tilted fault blocks on the eastern side of Tonto Basin and the western portion of the Salt River paleocanyon. The dip of bedding increases down-section from 0 to 27o providing evidence that deposition occurred while the faults were active. Lower Dagger Canyon conglomerate deposition began after 12.49 Ma, presumably due to base level fall associated with Basin and Range extension. The upper Dagger Canyon conglomerate is composed of flat-lying river gravels and sandstone located at higher elevations than the lower Dagger Canyon conglomerate in Tonto Basin and the Salt River paleocanyon. Deposition of the upper Dagger Canyon conglomerate began after 7.34 Ma and a possible a lag in fluvial deposition occurred between the two facies. If a lag in fluvial deposition occurred then the upper Dagger Canyon conglomerate represents a rejuvenation of the southwest-flowing river system in the Salt River paleocanyon after Basin and Range faulting waned. A likely driver for this rejuvenation would be southern Colorado Plateau uplift by the building of Mount Baldy volcanic field 12-8 Ma

Development and Implementation of Redox-Active Olefin Polymerization Catalysts

Investigating homogeneous polymerization catalysts has been a thriving area of chemistry in the academic realm for several decades now, and has helped drive the development of a range of materials, from designer plastics to cheap commodity polymers. Billions of pounds of these materials are produced every year, which ensures that continuing research in the area will be necessary to improve current processes and enable more economic use of our resources. This dissertation showcases the Long group’s research in homogeneous polymerization catalysis and our impact on the field thus far. We show that intelligent design of redox-active catalysts allows for a unique type of control over the polymerization process, enabling the production of multiple materials from a single, welldefined species. Specifically, we first demonstrate that polyolefin branching content may be reproducibly and predictably controlled via redox-active catalysts. We then use computational and experimental methods to delve into the mechanisms that allow a redox-active catalyst to have such unique behavior. Following this, we employ this newfound insight into redox-active olefin polymerization catalysts to design our own systems that allow access to more usable polymers. This dissertation will conclude with a glimpse at ongoing research as well as a perspective on how this area of research may be improved and expanded in the future

Topologies for ad-hoc networks utilizing directional antennas with restricted fields of view

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2006.Includes bibliographical references (p. 63-64).ORCLE (Optical/RF Combined Link Experiment), is an airborne network in which aircraft have multiple directional antennas that are restricted in their pointing direction. A pair of aircraft in ORCLE can be linked if they both have an antenna pointing at each other. Four topology algorithms, which coordinate the pointing of the antennas and attempt to maximize a connectedness metric, are presented and analyzed using a custom 2D simulation platform. Three of the algorithms are based on the Relative Neighbor Graph (RNG): the first constrains the RNG to requirements of the ORCLE network, the second augments the constrained RNG with edges from the Delaunay Triangulation, and the third algorithm tries to improve on the second by adding edges to reduce the diameter. The final algorithm uses a novel concept of overlapping sets of nested convex hulls to select the links of the network. All algorithms are stateless and interface with a Target Transition Layer, which gradually migrates topologies to prevent a large number of edges from being lost simultaneously. Scenes with varying node density, number of terminals per node, fields of view, and re-targeting delays are used to test the algorithms against a wide range of possible situations.by Brian C. Anderson.M.Eng

A Decision Support Technology Clearinghouse

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