A NASTRAN DMAP alter for linear buckling analysis under dynamic loading

A unique modification to the NASTRAN solution sequence for transient analysis with direct time integration (COSMIC NASTRAN rigid format 9) was developed and incorporated into a DMAP alter. This DMAP alter calculates the buckling stability of a dynamically loaded structure, and is used to predict the onset of structural buckling under stress wave loading conditions. The modified solution sequence incorporates the linear buckling analysis capability (rigid format 5) of NASTRAN into the existing Transient solution rigid format in such a way as to provide a time dependent eigensolution which is used to assess the buckling stability of the structure as it responds to the impulsive load. As a demonstration of the validity of this modified solution procedure, the dynamic buckling of a prismatic bar subjected to an impulsive longitudinal compression is analyzed and compared to the known theoretical solution. In addition, a dynamic buckling analysis is performed for the analytically less tractable problem of the localized dynamic buckling of an initially flawed composite laminate under transverse impact loading. The addition of this DMAP alter to the transient solution sequence in NASTRAN facilitates the prediction of both time and mode of buckling

A Phylogenetic Analysis of the African Plant Genus Palisota (family Commelinaceae) based on Chloroplast DNA Sequences

The plant genus Palisota (family Commelinaceae, or spiderwort family) consists of approximately 20 species and is distributed throughout the forests of tropical Africa. The genus exhibits several unusual morphological characteristics, and as a result has been difficult to classify based on morphology. Molecular phylogenetic studies have placed it near the base of Commelinaceae, but the exact placement of Palisota within the family is not clear. As the African continent has become more arid in recent geological times, the forests have receded, reducing the habitat for Palisota species and potentially impacting speciation and extinction rates within the genus. The goal of this study is to sequence the chloroplast-encoded gene rbcL in several additional species of Palisota and its relatives in order to: 1) determine the phylogenetic relationship of the genus with respect to other members of Commelinaceae; 2) evaluate phylogenentic relationships among species of Palisota; and 3) infer relative speciation/extinction rates within the genus. Additionally, we are exploring the use of other molecular regions for phylogenetic analysis with the genus

A fundamental study of clay drying using ware of large cross section

The drying of clay has been studied extensively in the past by many investigators, some of whom attempted to relate this information to the structure of clay and thereby develop a more vivid picture, while others studied the mechanism of drying in its own right in order to present a useable theory that would allow improvements in the drying operation. At present the literature is unable to present a theory of the mechanism of drying that is sufficiently general to cover the observed aspects of clay drying. Many and varied mechanisms are presented, but correlation is seldom completely evident between separate investigators. It is without question that the drying process is divided into two portions; (l) in which the rate of water loss is a constant and (2) in which the rate of water loss is not a constant but is decreasing in magnitude. This first drying period is designated the zone of constant rate, which appears as a straight horizontal line when the rate of water loss is plotted as the ordinate and percent water content of the sample (dry basis) as the abscissa. The second drying period or the falling rate zone is a key to the drying mechanism and is open to the most question. Norton has pictured this zone as a smooth curve slightly concave upward extending from the end of the constant rate zone to the origin. This indicates that the decrease in the rate of water loss is nearly uniform on a percent water content basis. Sherwood indicates that this falling rate zone may be separated into two parts, the first of which may or may not be a straight line while the second is slightly concave upward. Norton also indicates that the shrinkage of the clay in drying when plotted against water content begins as soon as drying is initiated and reaches zero in the order of 20% water content. It is the purpose of this investigation to determine the nature of the falling rate zone, and the water content where shrinkage ceases in order to better define the drying mechanism for clay. It is significant that much of the investigation into the mechanism of drying has been done on relatively small samples that may or may not characterize the drying nature of the clay itself. This study has been undertaken using samples of spherical shape whose plastic weight is in the order of 3000 grams and whose maximum wall thickness is 6 inches. It is believed that using samples of large cross section with minimum surface to volume ratio will provide more distinct definition of the particular rates at which water is lost. Equipment has been obtained that will allow control of the wet bulb temperature, the dry bulb temperature, which in turn fixes the percent relative humidity, and the air velocity. An automatic means of recording weight loss as a function of time, and shrinkage as a time function has been built --Introduction, pages 1-2

Low velocity impact analysis with NASTRAN

A nonlinear elastic force-displacement relationship is used to calculate the transient impact force and local deformation at the point of contact between impactor and target. The nonlinear analysis and transfer function capabilities of NASTRAN are used to define a finite element model that behaves globally linearly elastic, and locally nonlinear elastic to model the local contact behavior. Results are presented for two different structures: a uniform cylindrical rod impacted longitudinally; and an orthotropic plate impacted transversely. Calculated impact force and transient structural response of the targets are shown to compare well with results measured in experimental tests

Dynamic delamination buckling in composite laminates under impact loading: Computational simulation

A unique dynamic delamination buckling and delamination propagation analysis capability has been developed and incorporated into a finite element computer program. This capability consists of the following: (1) a modification of the direct time integration solution sequence which provides a new analysis algorithm that can be used to predict delamination buckling in a laminate subjected to dynamic loading, and (2) a new method of modeling the composite laminate using plate bending elements and multipoint constraints. This computer program is used to predict both impact induced buckling in composite laminates with initial delaminations and the strain energy release rate due to extension of the delamination. It is shown that delaminations near the outer surface of a laminate are susceptible to local buckling and buckling-induced delamination propagation when the laminate is subjected to transverse impact loading. The capability now exists to predict the time at which the onset of dynamic delamination buckling occurs, the dynamic buckling mode shape, and the dynamic delamination strain energy release rate

HISPANICS IN TEXAS HIGHER EDUCATION: AN ASSESSMENT OF THE STATE “CLOSING THE GAPS” INITIATIVE

Demographic changes associated with growth of the Hispanic and black population in the U.S. state of Texas have led politicians and policymakers to recognize that academic success in their ethnic and racial minority populations is a key to future statewide economic success. These demographic transitions require proactive state intervention to assure the earning power and intellectual prowess of the next generation. This study assesses the degree to which the Texas “Closing the Gaps” initiative has addressed the disparities in higher education among the state’s diverse populations

Flow-Induced Channel Formation in the Cytoplasm of Motile Cells

A model is presented to explain the development of flow channels within the cytoplasm of the plasmodium of the giant amoeba Physarum polycephalum. The formation of channels is related to the development of a self-organizing tubular network in large cells. Experiments indicate that the flow of cytoplasm is involved in the development and organization of these networks, and the mathematical model proposed here is motivated by recent experiments involving the observation of development of flow channel in small cells. A model of pressure-driven flow through a polymer network is presented in which the rate of flow increases the rate of depolymerization. Numerical solutions and asymptotic analysis of the model in one spatial dimension show that under very general assumptions this model predicts the formation of channels in response to flow