Deconstructing Voice-over-IP

Unified distributed configurations have led to many technical advances, including robots and flip-flop gates. In this work, authors show the synthesis of consistent hashing. We present new “fuzzy” archetypes, which we call ARGAS

Mutations in the TΨC Loop of E. coli tRNA(Lys,3 )Have Varied Effects on In Trans Complementation of HIV-1 Replication

BACKGROUND: Human immunodeficiency virus (HIV-1) exclusively selects and utilizes tRNA(Lys,3 )as the primer for initiation of reverse transcription. Several elements within the TΨC stem loop of tRNA(Lys,3 )are postulated to be important for selection and use in reverse transcription. The post-transcriptional modification at nucleotide 58 could play a role during plus-strand synthesis to stop reverse transcriptase from re-copying the tRNA primer. Nucleotides 53 and 54 within the TΨC stem loop of the tRNA have been shown to be important to form the complex between tRNA and the HIV-1 viral genome during initiation of reverse transcription. RESULTS: To further delineate the features of the TΨC stem loop of tRNA(Lys,3 )in reverse transcription, we have developed a complementation system in which E. coli tRNA(Lys,3 )is provided in trans to an HIV-1 genome in which the PBS is complementary to this tRNA. Successful selection and use of E. coli tRNA(Lys,3 )results in the production of infectious virus. We have used this single round infectious system to ascertain the effects that different mutants in the TΨC stem loop of tRNA(Lys,3 )have on complementation. Mutants were designed within the TΨC loop (nucleotide 58) and within the stem and loop of the TΨC loop (nucleotides 53 and 54). Analysis of the expression of E. coli tRNA(Lys,3 )mutants revealed differences in the capacity for aminoacylation, which is an indication of intracellular stability of the tRNA. Alteration of nucleotide 58 from A to U (A58U), T54G and TG5453CC all resulted in tRNA(Lys,3 )that was aminoacylated when expressed in cells, while a T54C mutation resulted in a tRNA(Lys,3 )that was not aminoacylated. Both the A58U and T54G mutated tRNA(Lys,3 )complemented HIV-1 replication similar to wild type E. coli tRNA(Lys,3). In contrast, the TG5453CC tRNA(Lys,3 )mutant did not complement replication. CONCLUSION: The results demonstrate that post-transcriptional modification of nucleotide 58 in tRNA(Lys,3 )is not essential for HIV-1 reverse transcription. In contrast, nucleotides 53 and 54 of tRNA(Lys,3 )are important for aminoacylation and selection and use of the tRNA(Lys,3 )in reverse transcription

Influence of the Neotyphodium--Tall Fescue Symbiosis on Belowground Processes

Much of the work to date on the relationships between cool season grasses and Neotyphodium fungal endophytes has focused on the physiological, biochemical, and genetic ramifications of the host-fungus relationship and the subsequent influence these effects have on ruminant nutrition, plant adaptation to environmental stresses, and aboveground ecological processes. Relatively little attention has been paid to effects on belowground parameters. In this paper, we review the research evaluating the impact of one endophyte-grass association, the Neotyphodium – tall fescue symbiosis, on underground ecological and biogeochemical processes. We also present some preliminary data showing that the quantity and nature of tall fescue root exudates are influenced by the plant cultivar and fungal genotype. This body of work clearly indicates that effects of the Neotyphodium-tall fescue symbiosis extend to belowground processes; however, additional research is needed to understand the mechanisms driving many of the observed root and soil endophyte effects

Does Fungal Endophyte Infection Improve Tall Fescue’s Growth Response to Fire and Water Limitation?

Invasive species may owe some of their success in competing and co-existing with native species to microbial symbioses they are capable of forming. Tall fescue is a cool-season, non-native, invasive grass capable of co-existing with native warm-season grasses in North American grasslands that frequently experience fire, drought, and cold winters, conditions to which the native species should be better-adapted than tall fescue. We hypothesized that tall fescue’s ability to form a symbiosis with Neotyphodium coenophialum, an aboveground fungal endophyte, may enhance its environmental stress tolerance and persistence in these environments. We used a greenhouse experiment to examine the effects of endophyte infection (E+ vs. E−), prescribed fire (1 burn vs. 2 burn vs. unburned control), and watering regime (dry vs. wet) on tall fescue growth. We assessed treatment effects for growth rates and the following response variables: total tiller length, number of tillers recruited during the experiment, number of reproductive tillers, tiller biomass, root biomass, and total biomass. Water regime significantly affected all response variables, with less growth and lower growth rates observed under the dry water regime compared to the wet. The burn treatments significantly affected total tiller length, number of reproductive tillers, total tiller biomass, and total biomass, but treatment differences were not consistent across parameters. Overall, fire seemed to enhance growth. Endophyte status significantly affected total tiller length and tiller biomass, but the effect was opposite what we predicted (E−\u3eE+). The results from our experiment indicated that tall fescue was relatively tolerant of fire, even when combined with dry conditions, and that the fungal endophyte symbiosis was not important in governing this ecological ability. The persistence of tall fescue in native grassland ecosystems may be linked to other endophyte-conferred abilities not measured here (e.g., herbivory release) or may not be related to this plant-microbial symbiosis

Performance of endophyte infected tall fescue in Europe and North America

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Photocurrent Quantum Yield in Suspended Carbon Nanotube p–n Junctions

We study photocurrent generation in individual suspended carbon nanotube pn junctions using spectrally-resolved scanning photocurrent microscopy. Spatial maps of the photocurrent allow us to determine the length of the pn junction intrinsic region, as well as the role of the n-type Schottky barrier. We show that reverse-bias operation eliminates complications caused by the n-type Schottky barrier and increases the length of the intrinsic region. The absorption cross-section of the CNT is calculated using an empirically verified model, and the effect of substrate reflection is determined using FDTD simulations. We find the room temperature photocurrent quantum yield is approximately 30% when exciting the carbon nanotube at the S₄₄ and S₅₅ excitonic transitions. The quantum yield value is an order of magnitude larger than previous estimates

A nanoscale pn junction in series with tunable Schottky barriers

PN junctions in nanoscale materials are of interest for a range of technologies including photodetectors, solar cells, and light-emitting diodes. However, Schottky barriers at the interface between metal contacts and the nanomaterial are often unavoidable. The effect of metal-semiconductor interfaces on the behavior of nanoscale diodes must be understood, both to extract the characteristics of the pn junction, and to understand the overall characteristics of the final device. Here, we study the current-voltage characteristics of diodes that are formed in fully suspended carbon nanotubes (CNTs). We utilize tunable Schottky barrier heights at the CNT-metal interface to elucidate the role of the Schottky barriers on the device characteristics. We develop a quantitative model to show how a variety of device characteristics can arise from apparently similar devices. Using our model we extract key parameters of the Schottky barriers and the pn junction, and predict the overall I-V characteristics of the device. Our equivalent circuit model is relevant to a variety of nanomaterial-based diode devices that are currently under investigation