2,019 research outputs found
Acquisition of an Agrobacterium Ri Plasmid and Pathogenicity by Other -Proteobacteria in Cucumber and Tomato Crops Affected by Root Mat
Root mat of cucumbers and tomatoes has previously been shown to be caused by Agrobacterium radiobacter strains harboring a root-inducing Ri plasmid (pRi). Nine other pRi-harboring -Proteobacteria have subsequently been isolated from root mat-infected crops. Fatty acid profiling and partial 16S rRNA sequence analysis identified three of these strains as being in the genus Ochrobactrum, five as being in the genus Rhizobium, and one as being in the genus Sinorhizobium. An in vitro pathogenicity test involving inoculation of cucumber cotyledons was developed. All pRi-harboring -Proteobacteria induced typical root mat symptoms from the cotyledons. Average transformation rates for rhizogenic Ochrobactrum (46%) and Rhizobium (44%) strains were lower than those observed for rhizogenic A. radiobacter strains (64%). However, individual strains from these three genera all had transformation rates comparable to those observed from cotyledons inoculatedwith a rhizogenic Sinorhizobium strain (75%)
Phylogenies of atpD and recA support the small subunit rRNA-based classification of rhizobia
The current classification of the rhizobia (root-nodule symbionts) assigns them to six genera. It is strongly influenced by the small subunit (16S, SSU) rRNA molecular phylogeny, but such single-gene phylogenies may not reflect the evolution of the genome as a whole. To test this, parts of the atpD and recA genes have been sequenced for 25 type strains within the alpha -Proteobacteria, representing species in Rhizobium, Sinorhizobium, Mesorhizobium, Bradyrhizobium, Azorhizobium, Agrobacterium, Phyllobacterium, Mycoplana and Brevundimonas. The current genera Sinorhizobium and Mesorhizobium are well supported by these genes, each forming a distinct phylogenetic clade with unequivocal bootstrap support. There is good support for a Rhizobium clade that includes Agrobacterium tumefaciens, and the very close relationship between Agrobacterium rhizogenes and Rhizobium tropici is confirmed. There is evidence for recombination within the genera Mesorhizobium and Sinorhizobium, but the congruence of the phylogenies at higher levels indicates that the genera are genetically isolated. rRNA provides a reliable distinction between genera, but genetic relationships within a genus may be disturbed by recombination
Spin resonance of 2D electrons in a large-area silicon MOSFET
We report electron spin resonance (ESR) measurements on a large-area silicon
MOSFET. An ESR signal at g-factor 1.9999(1), and with a linewidth of 0.6 G, is
observed and found to arise from two-dimensional (2D) electrons at the Si/SiO2
interface. The signal and its intensity show a pronounced dependence on applied
gate voltage. At gate voltages below the threshold of the MOSFET, the signal is
from weakly confined, isolated electrons as evidenced by the Curie-like
temperature dependence of its intensity. The situation above threshold appears
more complicated. These large-area MOSFETs provide the capability to
controllably tune from insulating to conducting regimes by adjusting the gate
voltage while monitoring the state of the 2D electron spins spectroscopically.Comment: 7 pages, 3 figures, submitted to Physica E special edition for
EPS2DS-1
The importance of accounting for parameter uncertainty in SF-6D value sets and its impact on studies that use the SF-6D to measure health utility
Background: The parameter uncertainty in the six-dimensional health state short form (SF-6D) value sets is commonly ignored. There are two sources of parameter uncertainty: uncertainty around the estimated regression coefficients and uncertainty around the model’s specification. This study explores these two sources of parameter uncertainty in the value sets using probabilistic sensitivity analysis (PSA) and a Bayesian approach. Methods: We used data from the original UK/SF-6D valuation study to evaluate the extent of parameter uncertainty in the value set. First, we re-estimated the Brazier model to replicate the published estimated coefficients. Second, we estimated standard errors around the predicted utility of each SF-6D state to assess the impact of parameter uncertainty on these estimated utilities. Third, we used Monte Carlo simulation technique to account for the uncertainty on these estimates. Finally, we used a Bayesian approach to quantifying parameter uncertainty in the value sets. The extent of parameter uncertainty in SF-6D value sets was assessed using data from the Hong Kong valuation study. Results: Including parameter uncertainty results in wider confidence/credible intervals and improved coverage probability using both approaches. Using PSA, the mean 95% confidence intervals widths for the mean utilities were 0.1394 (range: 0.0565–0.2239) and 0.0989 (0.0048–0.1252) with and without parameter uncertainty whilst, using the Bayesian approach, this was 0.1478 (0.053–0.1665). Upon evaluating the impact of parameter uncertainty on estimates of a population’s mean utility, the true standard error was underestimated by 79.1% (PSA) and 86.15% (Bayesian) when parameter uncertainty was ignored. Conclusions: Parameter uncertainty around the SF-6D value set has a large impact on the predicted utilities and estimated confidence intervals. This uncertainty should be accounted for when using SF-6D utilities in economic evaluations. Ignoring this additional information could impact misleadingly on policy decisions
Quasi-1D dynamics and nematic phases in the 2D Emery model
We consider the Emery model of a
Cu-O plane of the high temperature superconductors. We show that in a
strong-coupling limit, with strong Coulomb repulsions between electrons on
nearest-neighbor O sites, the electron-dynamics is strictly one dimensional,
and consequently a number of asymptotically exact results can be obtained
concerning the electronic structure. In particular, we show that a nematic
phase, which spontaneously breaks the point- group symmetry of the square
lattice, is stable at low enough temperatures and strong enough coupling.Comment: 8 pages, 5 eps figures; revised manuscript with more detailed
discussions; two new figures and three edited figuresedited figures; 14
references; new appendix with a detailed proof of the one-dimensional
dynamics of the system in the strong coupling limi
Sound Propagation in Nematic Fermi Liquid
We study the longitudinal sound propagation in the electronic nematic Fermi
liquid where the Fermi surface is distorted due to the spontaneously broken
rotational symmetry. The behavior of the sound wave in the nematic ordered
state is dramatically different from that in the isotropic Fermi liquid. The
collective modes associated with the fluctuations of the Fermi surface
distortion in the nematic Fermi liquid leads to the strong and anisotropic
damping of the sound wave. The relevance of the nematic Fermi liquid in doped
Mott insulator is discussed.Comment: 4 pages, no figur
Avoided Critical Behavior in a Uniformly Frustrated System
We study the effects of weak long-ranged antiferromagnetic interactions of
strength on a spin model with predominant short-ranged ferromagnetic
interactions. In three dimensions, this model exhibits an avoided critical
point in the sense that the critical temperature is strictly greater
than . The behavior of this system at temperatures less
than is controlled by the proximity to the avoided critical point.
We also quantize the model in a novel way to study the interplay between
charge-density wave and superconducting order.Comment: 32 page Latex file, figures available from authors by reques
Simultaneous identification of damping coefficient and initial value for PDEs from boundary measurement
Agronomic and silage quality traits of forage sorghum cultivars in 1995
Agronomic and silage quality traits were
measure d for 37 forage sorghum cultivars and
three grain sorghum hybrids. The 1995 growing
season was characterized by above average
rainfall in the spring and early summer, and a
hard freeze on September 22. At the time of
the freeze, 20 cultivars had reached the early-milk
to early-dough stage, 12 were in the
bloom stage, and the remaining eight were still
in the early- to late-boot stage . The late planting
date and low plant populations resulted in
below-normal whole-plant D M and grain yields.
Plant height s for the grain sorghums were near
normal, but the forage sorghums were well
below expected plant heights. The preensiled,
whole-plan t DM contents of the 37 forage
sorghums ranged from 23.0 to 39.9%. As
expected , the silage nutritive value traits of CP,
NDF, and ADF were most favorable for the
three grain sorghum hybrids and least favorable
for the eight forage sorghum hybrids that were
still in the boot stage when the freeze occurred
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