Definite Determinantal Representations of Ternary Hyperbolic Forms

We give a new and completely algebraic proof of the Helton-Vinnikov Theorem stating that every hyperbolic polynomial in three variables admits a definite linear determinantal representation

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Prehistoric Plant Procurement, Food Production, and Land Use in Southwestern Tamaulipas, Mexico

In this dissertation, I examine plant use, food production, and land use in the Ocampo region of southwestern Tamaulipas, northeastern Mexico. In the early 1950s Richard S. MacNeish excavated in a series of dry cave sites within the study area and discovered evidence for the local adoption of domesticated plants and the subsequent development of a mixed foraging-farming economy that persisted for millennia, before culminating in the establishment of settled farming villages. This research remains central to discussions of early Mesoamerican agriculture. However, the spectrum of land use and wild plant utilization over the prehistoric sequence remains poorly understood, as MacNeish\u27s Ocampo investigations focused on one aspect of a larger settlement pattern: cave occupations), and his results are incompletely published. This dissertation expands on earlier work through an examination of curated plant collections from MacNeish\u27s excavations and an archaeological survey near the Ocampo caves. Although most published sources acknowledge that wild plants comprised the majority of the local diet: especially during the early cultural phases), these sources often do not describe the species in question. Inspection of plant materials curated in several facilities in the United States and Mexico revealed a range of wild plants that are not mentioned previously in publication. Some curated specimens indicate that even when local populations lived in permanent habitations in villages, foraging activities drew them as far as 30 km away. Observations of present-day casual cultivation behaviors provided insights into how the earliest domesticated plants in the region: squashes and gourds) may have been incorporated into a primarily hunter-gatherer economy with minimal disruptions. Archaeological survey of the study area revealed that during the peak of population density: ca. 2400-1000 B.P.), large agricultural villages were established not only in narrow river valleys but also on moderate mountain slopes and high summits, likely due to a general lack of level land. Traditional farmers here today practice slash-and-burn agriculture on steep hill sides as flat alluvial terraces and gentle slopes become less available, and it is probable that prehistoric villagers did the same. Even as large permanent settlements became abundant, caves continued to be used for a variety of pursuits, including base camps for wild plant harvesting, winter-season hunting camps, and burial of the dead. Major contributions of this work include: 1) insights into the non-agricultural plant component of early low-level food producing economies in the study area; 2) availability of an important archaeobotanical data set previously not accessible to the general archaeological community; 3) refined classification of previously identified remains in the curated archaeobotanical collections; 4)increased awareness of the range of site types and land use practices utilized by early food producers in the Ocampo region: through preliminary archaeological survey and artifact assemblages on discovered sites); 5) documentation and registration of discovered sites with the in the Instituto Nacional de Antropologia e Historia: INAH) Registro Publico de Monumentos y Zonas Arqueológicos: Public Register of Archaeological Monuments and Zones ); and historically contextualize MacNeish\u27s groundbreaking investigations in the Ocampo caves

Improving Gulf Cordgrass Range.

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Damping Characteristics of Fibre Reinforced Polymers

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Positive Ulrich Sheaves

We provide a criterion for a coherent sheaf to be an Ulrich sheaf in terms of a certain bilinear form on its global sections. When working over the real numbers we call it a positive Ulrich sheaf if this bilinear form is symmetric or hermitian and positive definite. In that case our result provides a common theoretical framework for several results in real algebraic geometry concerning the existence of algebraic certificates for certain geometric properties. For instance, it implies Hilbert's theorem on nonnegative ternary quartics, via the geometry of del Pezzo surfaces, and the solution of the Lax conjecture on plane hyperbolic curves due to Helton and Vinnikov

National and Regional Impacts of U.S. Agricultural Exports

International Trade, Output, Employment, Exports, International Relations/Trade, Q10, Q11, Q13, Q17,

Long Term Financial Impacts of Drought Management Strategies

This paper analyzes the financial implications of drought management strategies for a model ranch in South Texas. The 2006 drought that affected Texas livestock producers left many cattlemen asking the age old question, "Should I cull to reduce my herd size or purchase feed to maintain my current herd".Livestock Production/Industries,