Concealed carry on college campuses

Suggests that handguns on college campuses would create problems for police and that concealed handgun training does not adequately prepare the license holder to interact during a crime in progress or a traffic stop

On the Origin of Fusiform Rust Resistance in Loblolly Pine

Studies of geographic variation in loblolly pine (Pinus taeda L.) have shown that seed sources from the western (generally west of the Mississippi River) and the northeastern part of the natural distribution are relatively resistant to fusiform rust, and those from elsewhere are susceptible. The greatest incidence of infection, on the other hand, is in the center of the distribution, exactly where the frequency of resistant genotypes is low. One might expect that the frequency of resistant genotypes would be higher where the disease is more prevalent, due to natural selection. It has been proposed that (1) fusiform rust resistance in loblolly pine in the west originates from hybridization with shortleaf pine. It is well known that shortleaf is resistant to fusiform rust, and it is also known that natural hybrids between the two species exist, and they seem to be more common in the west. (2) In the northeastern loblolly, it has been proposed that hybridization with pond pine is the source of resistance. Once again, natural hybridization between loblolly and pond pine is known to exist in the northeast, but not much is known about the relative resistance of pond pine to fusiform rust. Allozyme data was used to refute hypothesis (1) and cortical monoterpene data was used to refute hypothesis (2). A hypothesis is proposed involving selection during the Pleistocene to explain the present pattern of resistance and the development of a gene-for-gene pathosystem.Papers and abstracts from the 27th Southern Forest Tree Improvement Conference held at Oklahoma State University in Stillwater, Oklahoma on June 24-27, 2003

Evolution of Disease Response Genes in Loblolly Pine: Insights from Candidate Genes

BACKGROUND: Host-pathogen interactions that may lead to a competitive co-evolution of virulence and resistance mechanisms present an attractive system to study molecular evolution because strong, recent (or even current) selective pressure is expected at many genomic loci. However, it is unclear whether these selective forces would act to preserve existing diversity, promote novel diversity, or reduce linked neutral diversity during rapid fixation of advantageous alleles. In plants, the lack of adaptive immunity places a larger burden on genetic diversity to ensure survival of plant populations. This burden is even greater if the generation time of the plant is much longer than the generation time of the pathogen. METHODOLOGY/PRINCIPAL FINDINGS: Here, we present nucleotide polymorphism and substitution data for 41 candidate genes from the long-lived forest tree loblolly pine, selected primarily for their prospective influences on host-pathogen interactions. This dataset is analyzed together with 15 drought-tolerance and 13 wood-quality genes from previous studies. A wide range of neutrality tests were performed and tested against expectations from realistic demographic models. CONCLUSIONS/SIGNIFICANCE: Collectively, our analyses found that axr (auxin response factor), caf1 (chromatin assembly factor) and gatabp1 (gata binding protein 1) candidate genes carry patterns consistent with directional selection and erd3 (early response to drought 3) displays patterns suggestive of a selective sweep, both of which are consistent with the arm-race model of disease response evolution. Furthermore, we have identified patterns consistent with diversifying selection at erf1-like (ethylene responsive factor 1), ccoaoemt (caffeoyl-CoA-O-methyltransferase), cyp450-like (cytochrome p450-like) and pr4.3 (pathogen response 4.3), expected under the trench-warfare evolution model. Finally, a drought-tolerance candidate related to the plant cell wall, lp5, displayed patterns consistent with balancing selection. In conclusion, both arms-race and trench-warfare models seem compatible with patterns of polymorphism found in different disease-response candidate genes, indicating a mixed strategy of disease tolerance evolution for loblolly pine, a major tree crop in southeastern United States

MOVPE Wachstum und Charakterisierung von Gruppe-III Nitriden mit in situ spektroskopischer Ellipsometrie

Das Ziel dieser Arbeit ist die Untersuchung der Wachstumsmechanismen der Gruppe III-Nitride GaN und InN in der metallorganischen Gasphasenepitaxie (MOVPE) mittels spektroskopischer Ellipsometrie (SE) in situ. Dabei ermöglicht SE einen direkten Zugang zu den Materialparametern wie Bandlückenenergie, Bandlückenverbreiterung, Schichtdicken- oder Rauhigkeitsentwicklung bereits während des Wachstumsprozesses. Das Verfolgen der Änderungen dieser Materialparameter in direkter Abhängigkeit der gewählten Wachstumsparameter erlaubt ein tieferes Verständnis der zugrunde liegenden Wachstumsmechanismen und eine gezielte Steuerung des Wachstumsprozesses. Beim Wachstum von GaN auf Saphir mit einer Gitterfehlanpassung von 16% hängt die Qualität der epitaktischen Schicht stark von der Präparation des Substrates und der Nukleationsschicht ab. Hier zeigt SE, daß der Nitridierungsprozeß des Saphirs unter Ammoniak bereits bei 800°C beginnt und sich nach etwa 10min bei 1060°C eine kristalline, 4nm dünne Schicht AlN gebildet hat. Das Nukleationsschichtwachstum selbst kann sehr sensitiv auf die kristalline Zusammensetzung in Abhängigkeit der Wachstumsrate und des V/III Verhältnisses gesteuert werden. Bei der thermischen Nachbehandlung der Nukleationsschicht zum Erreichen der Wachstumstemperatur für die Epitaxieschicht (annealing) wird mit SE eine Phasenumwandlung von kubischem zu hexagonalem GaN beobachtet. Diese ist allerdings mit Erreichen der Schichtwachstumstemperatur abgeschlossen. Eine Langzeitbehandlung verschlechtert die Qualität, die Nukleationsschicht desorbiert. Auch ermöglicht SE die Einflüsse von Umgebungsparametern wie z.B. der Reaktorbelegung zu quantifizieren und die dadurch veränderte Wachstumsrate der Nukleationsschicht zu korrigieren. GaN Epitaxieschichten, die auf so optimierten Nukleationsschichten gewachsen werden, zeigen niedrige Röntgen-Halbwertsbreiten, ausgeprägte Photolumineszenz gebundener und freier Exzitonen sowie atomar glatte Oberflächen. Sie sind von hoher Qualität. Der Vergleich von MOVPE Oberflächen während des Wachstums mit (PA)MBE präparierten Oberflächen mittels SE zeigt außerdem, daß das MOVPE Wachstum offensichtlich mit einer mit Stickstoff terminierten Oberfläche einhergeht. Schließlich ermöglicht SE die Optimierung des Wachstums von InN auf Saphir in der MOVPE. Die Bestimmung der dielektrischen Funktion des so hergestellten InN zeigt eine Bandlückenenergie von etwa 1eV sowie drei höhere Interbandübergänge bei 4,85eV, 5,40eV und 6,17eV in guter Übereinstimmung mit bereits veröffentlichten theoretischen Berechnungen.This work deals with the epitaxial growth and growth characterization of the binary group-III nitrides gallium-nitride (GaN) and indium-nitride (InN) using in situ Spectroscopic Ellipsometry (SE) for growth monitoring. The outstanding performances like a vast spectal range of their optical band gap energy from 3.4eV (360nm) for GaN down to may be 0.7eV (1770nm) for InN bring them into the focus of the researcher society all over the world. As epitaxial growth is usually performed in metal-organic vapor phase epitaxy (MOVPE) on highly lattice mismatched substrates, a detailed analysis of the growth mechanisms and the growth process requires in situ optical techniques. SE is the method of choice here which allows determination of epitaxial layer properties during growth from the sub-nm to micrometer scale. To completely understand the results attained in MOVPE, SE is used for comparison to other growth techniques such as plasma-assisted molecular beam epitaxy (PA)MBE in a vacuum environment to access to the structural properties of the sample surfaces during growth via electron based characterization methods. SE already reveals the fundamental processes of sapphire nitridation which can be used to reduce the high lattice mismatch between substrate and epilayer of 16%. Here nitridation begins already at 800°C in an ammonia atmosphere leading to a cristalline layer of 4nm thickness after 10min at 1060°C. Growth of the GaN nucleation layer (NL) can be controlled with respect to the cristalline stoichiometry in the NL depending on parameters such as growth rate and V/III ratio of the precursors. The subsequent annealing process of the NL to the growth temperature of the GaN epilayer reveals a phase transition inside the NL from cubic to hexagonal GaN. This transition is already finished when the high growth temperature is reached. Long term annealing leads to reduced material quality and the NL desorbs with a rate of 1.4nm/min at 1060°C. Furthermore SE allows to quantify influences like reactor coverage with GaN from former epitaxial runs and to correct the resulting changes in NL growth rates. GaN epilayer grown on such optimized NL are of high quality, showing low X-ray full width at half maximum (FWHM) of the (0002) reflex, pronounced photoluminescence of free and bound excitons and atomar flat surfaces. For analysis of the epitaxial growth conditions and to get insight into the surface termination at high temperatures additional (PA)MBE growth is performed. Here through preparation and analysis of different GaN surface states in (PA)MBE SE clearly reveals a nitrogen covered surface during MOVPE of GaN. Finally InN growth on sapphire is optimized by the aid of SE and thin InN layer are achieved again showing low X-ray FWHM, pronounced A1 and E2 Raman modes and a band edge of around 1eV from SE analysis. The InN dielectric function determined from these layers show three higher interband transitions positioned at 4.85eV, 5.40eV, and 6.17eV in agreement with theoretical calculations published previously

Evolutionary relationships of Slash Pine (Pinus elliottii) with its temperate and tropical relatives

llozymes in bud tissue and monoterpene contents in xylem oleoresin of slash pine (Pinus elliottii) were analyzed from populations across the natural distribution, as well as those from other species in the AUSTRALES pines. Allozyme diversity measures of slash pine were similar to those found in other southern pines. The two slash pine varieties, the slower-growing south Florida variety (var. densa) and the more commercial ";typical"; variety (var. elliottii), were not separated in the cluster analysis of allozymes. Variation was continuous from south to north in Florida in slash pine, with no distinct transition between the two varieties. The monoterpene data also showed continuous variation between the two slash pine varieties. Expected heterozygosity declined from south to north, supporting the hypothesis that slash pine resided in a Pleistocene refugium in south Florida or the Caribbean, migrating northward at the close of the ice age. Allozyme frequencies as well as monoterpene compositions of slash pine and its AUSTRALES relatives showed a very close relationship between slash pine and Bahamian Caribbean pine (P. caribaea Morelet var bahamensis). Southern African Forestry Journal No.190 2001: 73-7