The Phosphorns Sorption Potential of Selected Hawaiian Soils in Relation to Their Mineralogy and Chemistry

Eleven soils from Hawaii representing a wide range in properties that affect P sorption were used to quantify the effects of those factors on P sorption. The results were evaluated for a property's possible utility in predicting P sorption, which is important for improving P fertility management. Phosphorus buffering coefficients calculated from an incubation study and P sorbed at 0.2 mg P L’^ in solution from sorption isotherm data were correlated with soil properties. A prediction of the number of sorption sites per gram of soil was the property that best predicted P sorption. The number of sorption sites per gram were predicted from analysis of X-ray diffraction patterns that indicated the quantity and average size of crystallites for each mineral in a soil. The results indicate a strong dependency of P sorption on soil mineral type and content with less influence of other soil properties. Data from a 180 day incubation study were fit with a negative exponential equation, the parameters of which indicate the proportions of P sorbed instantaneously and sorbed with time. The parameter estimate associated in instantaneous P sorption was most closely related with the number of sorption sites. The parameter estimates did not correlate with other properties, indicating that other unmeasured -factors have an influence on the P sorption process

A Cytotoxic, Co-operative Interaction Between Energy Deprivation and Glutamate Release From System x\u3csub\u3ec\u3c/sub\u3e\u3csup\u3e−\u3c/sup\u3e Mediates Aglycemic Neuronal Cell Death

The astrocyte cystine/glutamate antiporter (system xc−) contributes substantially to the excitotoxic neuronal cell death facilitated by glucose deprivation. The purpose of this study was to determine the mechanism by which this occurred. Using pure astrocyte cultures, as well as, mixed cortical cell cultures containing both neurons and astrocytes, we found that neither an enhancement in system xc− expression nor activity underlies the excitotoxic effects of aglycemia. In addition, using three separate bioassays, we demonstrate no change in the ability of glucose-deprived astrocytes—either cultured alone or with neurons—to remove glutamate from the extracellular space. Instead, we demonstrate that glucose-deprived cultures are 2 to 3 times more sensitive to the killing effects of glutamate or N-methyl-D-aspartate when compared with their glucose-containing controls. Hence, our results are consistent with the weak excitotoxic hypothesis such that a bioenergetic deficiency, which is measureable in our mixed but not astrocyte cultures, allows normally innocuous concentrations of glutamate to become excitotoxic. Adding to the burgeoning literature detailing the contribution of astrocytes to neuronal injury, we conclude that under our experimental paradigm, a cytotoxic, co-operative interaction between energy deprivation and glutamate release from astrocyte system xc− mediates aglycemic neuronal cell death

Organizational Capacity and Progress Plateaus in the Flight Training Environment

Capacity is the ability of an organization to achieve its overall mission and satisfy stakeholder expectations. Stakeholders in a flight training organization include the owners and/or their representatives, flight school managers, instructor pilots, and the student pilots. This study was an examination of the organizational capacity of student pilots through a progress plateau theoretical lens using a mixed methodological approach and participants from a collegiate aviation program. Student pilot progress plateaus were found to have an adverse unrealized capacity consequence for the stakeholders in the organization. Recommendations to improve organizational capacity include the identification of progress plateaus utilizing flight training progress charts followed by the intervention of flight school leaders to resolve the plateau

Comparative Examination of Plasmoid Ejection at Mercury, Earth, Jupiter, and Saturn

The onset of magnetic reconnection in the near-tail of Earth, long known to herald the fast magnetospheric convection that leads to geomagnetic storms and substorms, is very closely associated with the formation and down-tail ejection of magnetic loops or flux ropes called plasmoids. Plasmoids form as a result of the fragmentation of preexisting cross-tail current sheet as a result of magnetic reconnection. Depending upon the number, location, and intensity of the individual reconnection X-lines and how they evolve, some of these loop-like or helical magnetic structures may also be carried sunward. At the inner edge of the tail they are expected to "re-reconnect' with the planetary magnetic field and dissipate. Plasmoid ejection has now been observed in the magnetotails of Mercury, Earth, Jupiter, and Saturn. These magnetic field and charged particle measurements have been taken by the MESSENGER, Voyager, Galileo, Cassini, and numerous Earth missions. Here we present a comparative examination of the structure and dynamics of plasmoids observed in the magnetotails of these 5 planets. The results are used to learn more about how these magnetic structures form and to assess similarities and differences in the nature of magnetotail reconnection at these planets

islet Reveals Segmentation in the Amphioxus Hindbrain Homolog

AbstractThe vertebrate embryonic hindbrain is segmented into rhombomeres. Gene expression studies suggest that amphioxus, the closest invertebrate relative of vertebrates, has a hindbrain homolog. However, this region is not overtly segmented in amphioxus, raising the question of how hindbrain segmentation arose in chordate evolution. Vertebrate hindbrain segmentation includes the patterning of cranial motor neurons, which can be identified by their expression of the LIM-homeodomain transcription factor islet1. To learn if the amphioxus hindbrain homolog is cryptically segmented, we cloned an amphioxus gene closely related to islet1, which we named simply islet. We report that amphioxus islet expression includes a domain of segmentally arranged cells in the ventral hindbrain homolog. We hypothesize that these cells are developing motor neurons and reveal a form of hindbrain segmentation in amphioxus. Hence, vertebrate rhombomeres may derive from a cryptically segmented brain present in the amphioxus/vertebrate ancestor. Other islet expression domains provide evidence for amphioxus homologs of the pineal gland, adenohypophysis, and endocrine pancreas. Surprisingly, homologs of vertebrate islet1-expressing spinal motor neurons and Rohon-Beard sensory neurons appear to be absent

Hedgehog signaling is required at multiple stages of zebrafish tooth development

Background. The accessibility of the developing zebrafish pharyngeal dentition makes it an advantageous system in which to study many aspects of tooth development from early initiation to late morphogenesis. In mammals, hedgehog signaling is known to be essential for multiple stages of odontogenesis; however, potential roles for the pathway during initiation of tooth development or in later morphogenesis are incompletely understood. Results. We have identified mRNA expression of the hedgehog ligands shha and the receptors ptc1 and ptc2 during zebrafish pharyngeal tooth development. We looked for, but did not detect, tooth germ expression of the other known zebrafish hedgehog ligands shhb, dhh, ihha, or ihhb, suggesting that as in mammals, only Shh participates in zebrafish tooth development. Supporting this idea, we found that morphological and gene expression evidence of tooth initiation is eliminated in shha mutant embryos, and that morpholino antisense oligonucleotide knockdown of shha, but not shhb, function prevents mature tooth formation. Hedgehog pathway inhibition with the antagonist compound cyclopamine affected tooth formation at each stage in which we applied it: arresting development at early stages and disrupting mature tooth morphology when applied later. These results suggest that hedgehog signaling is required continuously during odontogenesis. In contrast, over-expression of shha had no effect on the developing dentition, possibly because shha is normally extensively expressed in the zebrafish pharyngeal region. Conclusion. We have identified previously unknown requirements for hedgehog signaling for early tooth initiation and later morphogenesis. The similarity of our results with data from mouse and other vertebrates suggests that despite gene duplication and changes in the location of where teeth form, the roles of hedgehog signaling in tooth development have been largely conserved during evolution. © 2010 Jackman et al; licensee BioMed Central Ltd

NGTS-4b: A sub-Neptune transiting in the desert

We report the discovery of NGTS-4b, a sub-Neptune-sized planet transiting a 13th magnitude K-dwarf in a 1.34 d orbit. NGTS-4b has a mass M = 20.6 ± 3.0 M⊕ and radius R = 3.18 ± 0.26 R⊕, which places it well within the so-called ‘Neptunian Desert’. The mean density of the planet (3.45 ± 0.95 g cm−3) is consistent with a composition of 100  per cent H2O or a rocky core with a volatile envelope. NGTS-4b is likely to suffer significant mass loss due to relatively strong EUV/X-ray irradiation. Its survival in the Neptunian desert may be due to an unusually high-core mass, or it may have avoided the most intense X-ray irradiation by migrating after the initial activity of its host star had subsided. With a transit depth of 0.13 ± 0.02 per cent, NGTS-4b represents the shallowest transiting system ever discovered from the ground, and is the smallest planet discovered in a wide-field ground-based photometric survey

Detection of stellar flares and a transiting brown dwarf with the next generation transit survey

Stellar flares are explosive phenomena caused by reconnection events in the magnetic fields of stars. They emit across a wide range of wavelengths but notably in the optical, UV and in X-rays. They are some of the highest energy events seen from other stars and they regularly dwarf those seen from the Sun. They are regularly seen on low mass stars and provide a way of studying the magnetic activity of these systems. Their role in exoplanet habitability (in particular for low mass stars) has become increasingly relevant in recent years, necessitating studies of their energies and occurrence rates. In this thesis I present observations and analysis of stellar flares detected with the Next Generation Transit Survey (NGTS). These flares come from stars ranging from G to L spectral type. I also present the detection and analysis of the transiting brown dwarf NGTS-7Ab, discovered in part because of the multiple flares detected from the M dwarf host star. These flare detections include the first ground-based CCD detections of superflares from a G-type star, NGTS J030834.9-211322. I used the high cadence NGTS observations to apply a Solar inspired empirical flare model, one which does not require arbitrary break points between the flare rise and decay. I also present the detection of a giant flare from a pre-main sequence M star. This flare was one of the most energetic detected from an M star and displayed quasi-periodic pulsations in the flare peak. I apply solar techniques to analyse these oscillations and identify their cause. I present the first detection of a white-light flare from an L2.5 dwarf. This is the coolest star to ever show a white-light flare to date and shows strong tranxiii sient magnetic activity can persist to the brown dwarf boundary. I also show how full frame images in wide-field exoplanet surveys, provided they are a high enough cadence, can be used to detect flares from the faintest and coolest stars. I present the detection of NGTS-7Ab, an ultra-short period brown dwarf around a tidally locked and active M star. I analyse the entire system, showing through a kinematic and photometric analysis that it is likely a hierarchical triple system formed of two active M stars (NGTS-7A and NGTS-7B) and a transiting brown dwarf (NGTS-7Ab). This is the shortest period transiting brown dwarf discovered to date and it has spun up and tidally locked its host star, placing the system in a state of spin-orbit synchronisation. Finally, I discuss the detection of white-light flares from pre-main sequence stars associated with the Orion complex. These stars have an average age of 4 Myr. I measure the average flare occurrence rate for M0-M3 stars, finding a non-linear relationship between flare occurrence rate and cluster age. My work shows how the ground-based NGTS observations can rival those available from space for high energy white-light flare events. Throughout this work I also discuss the possible effects flares may have on nearby exoplanets, along with how the detected flare events relate to other signs of magnetic activity such as starspots