Dynamic delamination crack propagation in a graphite/epoxy laminate

Dynamic delamination crack propagation in a (90/0) 5s Graphite/Epoxy laminate with an embedded interfacial crack was investigated experimentally using high speed photography. The dynamic motion was produced by impacting the beamlike laminate specimen with a silicon rubber ball. The threshold impact velocities required to initiate dynamic crack propagation in laminates with varying initial crack positions were determined. The crack propagation speeds were estimated from the photographs. Results show that the through the thickness position of the embedded crack can significantly affect the dominant mechanism and the threshold impact velocity for the onset of crack movement. If the initial delamination is placed near the top of bottom surface of the laminate, local buckling of the delaminated plies may cause instability of the crack. If the initial delamination lies on the midplane, local buckling does not occur and the initiation of crack propagation appears to be dominated by Mode II fracture. The crack propagation and arrest observed was seen to be affected by wave motion within the delamination region

Spatially-Resolved Temperature Diagnostic for Supersonic Flow Using Cross-Beam Doppler-Limited Laser Saturation Spectroscopy

Optical techniques for measuring the temperature in three-dimensional supersonic reactive flows have typically depended on lineshape measurements using single-beam laser absorption spectroscopy. However, absorption over extended path lengths in flows with symmetric, turbulent eddies can lead to systematically high extracted temperatures due to Doppler shifts resulting from flow along the absorption path. To eliminate these problems, Cross-Beam Saturation Absorption Spectroscopy (CBSAS) and Cross-Beam Inter-Modulated Fluorescence (CBIMF) have been developed which utilize two crossed and nearly copropogating laser beams.to record the spectral signal of an I2 ro-vibrational line in a small three-dimensional volume using a tunable CW dye laser. Temperature is extracted by fitting the recorded signal with a theoretical signal constructed from the Doppler-broadened hyperfine components of the ro-vibrational line. The CBIMF technique proved successful for extracting the temperature of an I2-seeded, Ar gas flow within a small, Mach 2, Laval nozzle where the overlap volume of the two 1 mm diameter laser beams was 2.4 mm3. At a test point downstream of the nozzle throat, the average temperature of 146 K ± 1.5 K extracted from measurements of the I2 P(46) 17-1 spectral line compared favorably with the 138 K temperature calculated from isentropic, one-dimensional flow theory

Role of p24 Proteins in Regulating Reproductive Behavior

The organism Drosophila melanogaster, otherwise known as the fruit fly, has proven to be a respectable genetic model for analyzing behavior. Genes function within signaling pathways to regulate a variety of behavioral responses, such as ovulation and egg laying. Our gene family of interest consists of nine p24 genes that encode for 24 kD transmembrane proteins. When the expression of p24 genes logjam, eclair, or baiser is lost, adult females do not oviposit eggs. These genes may be responsible for trafficking cargo vesicles from the endoplasmic reticulum to the Golgi apparatus within cells. Therefore, we hypothesize that the function of p24 proteins is to traffic an ovulation or oviposition signal within a specialized set of cells. Unfortunately specificities regarding the function and localization of p24s remain unidentified. In order to determine function, we characterized p24 localization in a variety of D. melanogaster tissues using p24-specific antisera. We discovered that p24 proteins are expressed in an assortment of tissues in the fly, especially in the nervous system and reproductive tissues. Co-immunostaining of p24 proteins and peptidergic cell markers showed an association between p24-expressing and peptide secreting cells, thus supporting the hypothesis that p24s function in the relaying of signals for neuropeptide secretion. If the trafficking of signals is blocked due to the lack of p24 gene function, then neuropeptides controlling ovulation and egg laying would not be secreted, and eggs would not be oviposited as seen in some p24-deficient animals. There is evidence that two specific neurotransmitters, octopamine and glutamate, synergistically control egg laying behavior. It is possible that p24 mutants are deficient in the release of these neurotransmitters. To test this hypothesis, eclair and logjam mutants were fed octopamine and glutamate in order to restore egg-laying behavior. We discovered that feeding mutant females these neurotransmitters did not restore egg laying. Therefore, the defect is most likely not due to the loss of neurotransmitters. However, we have theorized ideas of possible issues with the p24-deficient fly

Cryptoendolith alteration of Antarctic sandstone substrates: pioneers or opportunists?

The cryptoendolithic habitat of the Antarctic Dry Valleys has been considered a good analogy for past Martian ecosystems, if life arose on the planet. Yet cryptoendoliths are thought to favor the colonization of rocks that have a preexisting porous structure, e. g., sandstones. This may weaken their significance as exact analogues of potential rock-colonizing organisms on Mars, given our current understanding of the dominant volcanic nature of Martian geology. However, the production of oxalic acid, by these lichendominated communities, and its weathering potential indicate that it could be an aid in rock colonization, enabling endoliths to inhabit a wider variety of rock types. Utilizing ICP-AES and scanning electron microscope techniques, this study investigates elemental and mineralogical compositions within colonized and uncolonized layers in individual sandstone samples. This is in order to determine if the weathering of mineral phases within the colonized layers causes an increase in the amount of pore space available for colonization. The results show that colonized layers are more weathered than uncolonized, deeper portions of the rock substrate. Layers within uncolonized samples have uniform compositions. Differences between the colonized and uncolonized layers also occur to varying extents within colonized rocks of different mineralogical maturities. The results confirm that cryptoendoliths modify their habitat through the production of oxalic acid and suggest that over time this directly increases the porosity of their inhabited layer, potentially increasing the biomass it can support

Identifying Best Practices for a Successful Study Abroad Program

The purpose of this study was to identify the best practices of study abroad programs before, during, and after the experience. The results of this study will add further to implementing quality educational programs in agricultural and life sciences. A qualitative methodology with participant observation was employed to provide a thick and rich examination of a study abroad experience conducted in Latin America. Results provided specific best practices for activities before, during, and after such an experience. Recommendations and implications are provided

The carbon and nitrogen stable isotope geochemistry of two lunar meteorites: ALHA-81005 and Y-86032

The carbon and nitrogen stable isotope geochemistry of two lunar meteorites, ALHA-81005 and Y-86032 has been compared with that of an Apollo 16 regolith breccia, 60016. Although much of the carbon present in all three samples is terrestrial organic contamination, the meteorites have higher carbon abundances and lighter isotopic compositions than 60016. The non-contaminant carbon in ALHA-81005 and Y-86032 occurs as two distinct components, combusting between 550-700℃ and 900-1100℃. Since these components are absent from the pristine lunar breccia, they must have been added (i) from the impactor which ejected the meteorites from the Moon; (ii) in the Antarctic or (iii) be representative of a lunar environment not sampled by Apollo missions. At temperatures over 1100℃, spallogenic carbon combusts, with elevated δ^C, greater than 0‰. Nitrogen systematics are less-well resolved than carbon, partly due to the lower amounts of nitrogen gas liberated by the meteorites. Nitrogen abundance of ALHA-81005 and Y-86032 fall in the range of values from lunar breccias and δ^N values follow the heavy-light-heavy pattern characteristic of such samples. Spallogenic carbon and nitrogen are more abundant in ALHA-81005 than Y-86032,in keeping with its longer exposure age. Nitrogen data are consistent with identification of ALHA-81005 and Y-86032 as lunar highland breccias compacted from immature regolithic material