Sewanee: The University of the South

About: Sewanee: The University of the South is a education organization based out in Sewanee, Tennessee, United States. It is known for research contribution in the topics: Population & Species richness. The organization has 8995 authors who have published 14790 publications receiving 320138 citations. The organization is also known as: Sewanee & The University of the South.

Linear, non-linear optical susceptibilities and the hyperpolarizability of the mixed crystals Ag0.5Pb1.75Ge(S1−xSex)4: experiment and theory

Abstract: As the starting point for a comprehensive theoretical investigation of the linear and nonlinear optical susceptibilities, we have used our experimental crystallographic data for Ag05Pb175GeS3Se (Ag2Pb7Ge4S12Se4) reported The experimental crystallographic positions were optimized by minimizing the forces acting on each atom to get meaningful theoretical predictions of the optical properties The linear optical susceptibilities are calculated We find that the optical band gap shows very good agreement with our measured gap The second-order nonlinear optical (NLO) susceptibilities dispersion namely the optical second harmonic generation (SHG) is calculated and compared with our experimental measurements The microscopic first order hyperpolarizability, β123, vector component along the principal dipole moment directions for the χ(2)123(ω) component was obtained theoretically and compared with our measured values at different temperatures The dependence of the two-photon absorption (TPA) for the pump-probing at SHG of the microsecond CO2 laser was measured In addition we explored the linear electro-optical effect in these crystals This effect is described by the third rank polar tensors similarly to the SHG However, for the Pockels effect besides the electronic contribution, the phonon subsystem also begins to play a principal role As a consequence we study the dispersion of the linear electro-optical effects in the mentioned crystals

A unique pseudanabaenalean (cyanobacteria) genus nodosilinea gen. nov. based on morphological and molecular data(1).

Abstract: The cyanobacteria are a diverse, ancient lineage of oxygenic, phototrophic bacteria. Ubiquitous in nearly all ecosystems, the alpha-level diversity of these organisms lags behind other algal lineages due to a perceived dearth of phylogenetically useful characters. Recent phylogenetic studies of species within the genus Leptolyngbya have demonstrated that this is a polyphyletic assemblage. One group of strains that fits within the current circumscription of Leptolyngbya is genetically and phylogenetically distinct from Leptolyngbya sensu stricto. Members of this clade possess both a morphological synapomorphy and shared 16S-23S internal transcribed spacer (ITS) secondary structure, allowing the diagnosis of the new cyanobacterial genus Nodosilinea. Members of this genus are united by the unique ability to form nodules along the length of the filament. This trait has been previously observed only in the species Leptolyngbya nodulosa Z. Li et J. Brand, and we have chosen this species as the generitype of Nodosilinea. We currently recognize four species in the genus, N. nodulosa (Z. Li et J. Brand) comb. nov., N. bijugata (Kong.) comb. nov., N. conica sp. nov., and N. epilithica sp. nov.

Hyperprolinemic larvae of the drosophilid fly, Chymomyza costata, survive cryopreservation in liquid nitrogen

Abstract: The larva of the drosophilid fly, Chymomyza costata, is probably the most complex metazoan organism that can survive submergence in liquid nitrogen (-196 °C) in a fully hydrated state. We examined the associations between the physiological and biochemical parameters of differently acclimated larvae and their freeze tolerance. Entering diapause is an essential and sufficient prerequisite for attaining high levels of survival in liquid nitrogen (23% survival to adult stage), although cold acclimation further improves this capacity (62% survival). Profiling of 61 different metabolites identified proline as a prominent compound whose concentration increased from 20 to 147 mM during diapause transition and subsequent cold acclimation. This study provides direct evidence for the essential role of proline in high freeze tolerance. We increased the levels of proline in the larval tissues by feeding larvae proline-augmented diets and found that this simple treatment dramatically improved their freeze tolerance. Cell and tissue survival following exposure to liquid nitrogen was evident in proline-fed nondiapause larvae, and survival to adult stage increased from 0% to 36% in proline-fed diapause-destined larvae. A significant statistical correlation was found between the whole-body concentration of proline, either natural or artificial, and survival to the adult stage in liquid nitrogen for diapause larvae. Differential scanning calorimetry analysis suggested that high proline levels, in combination with a relatively low content of osmotically active water and freeze dehydration, increased the propensity of the remaining unfrozen water to undergo a glass-like transition (vitrification) and thus facilitated the prevention of cryoinjury.

Habitat preferences of oak-feeding xylophagous beetles in a temperate woodland: implications for forest history and management

Abstract: Oaks host the richest fauna of saproxylic insect in Europe. We studied habitat preferences of two beetle families, Buprestidae and Cerambycidae, by rearing the beetles from standardised oak timber baits. Species density was higher in the understorey than in the canopy; and in sun-exposed baits if within the understorey. Insolation was the most important factor affecting the composition of reared assemblages (explaining ca. 30% of variation in the data), followed by vertical stratum (ca. 10%). Local dead wood volume had no effect. The high preference for sun-exposed wood located near the ground suggests that: (i) open-canopy woodlands had to be rather common in temperate Europe; (ii) oak-utilising xylophages would benefit from restoration of management practices such as coppicing or woodland pasture; (iii) the policy of increasing dead wood volume in commercial forests is principally correct, but its success will depend on dead wood location within the forests.

Autophagy as a pro-death pathway

Abstract: The evolutionarily conserved catabolic process of autophagy involves the degradation of cytoplasmic components through lysosomal enzymes. Basal levels of autophagy maintain cellular homeostasis and under stress conditions high levels of autophagy are induced. It is often under such stress conditions that high levels of autophagy and cell death have been observed, leading to the idea that autophagy may act as an executioner of cell death. However the notion of autophagy as a cell death mechanism has been controversial and remains mechanistically undefined. There is now growing evidence that in specific contexts autophagy can indeed facilitate cell death. The pro-death role of autophagy is however complicated due to the extensive cross-talk between different signalling pathways. This review summarises the examples of where autophagy acts as a means of cell death and discusses the association of autophagy with the different cell death pathways.