4,234 research outputs found
Raman scattering from phonons and magnons in RFe3)BO3)4
Inelastic light scattering spectra of several members of the RFe3(BO3)4
family reveal a cascade of phase transitions as a function of temperature,
starting with a structural, weakly first order, phase transition followed by
two magnetic phase transitions. Those consist of the ordering of the Fe-spin
sublattice revealed by all the compound, and a subsequent spin-reorientational
transition for GdFe3(BO3)4. The Raman data evidence a strong coupling between
the lattice and magnetic degrees of freedom in these borates. The Fe-sublattice
ordering leads to a strong suppression of the low energy magnetic scattering,
and a multiple peaked two-magnon scattering continuum is observed. Evidence for
short-range correlations is found in the `paramagnetic' phase by the
observation of a broad magnetic continuum in the Raman data, which persists up
to surprisingly high temperatures.Comment: 17 pages, 13 figure
An Adaptive Mutation in Enterococcus faecium LiaR Associated with Antimicrobial Peptide Resistance Mimics Phosphorylation and Stabilizes LiaR in an Activated State
The cyclic antimicrobial lipopeptide daptomycin (DAP) triggers the LiaFSR membrane stress response pathway in enterococci and many other Gram-positive organisms. LiaR is the response regulator that, upon phosphorylation, binds in a sequence-specific manner to DNA to regulate transcription in response to membrane stress. In clinical settings, non-susceptibility to DAP by Enterococcus faecium is correlated frequently with a mutation in LiaR of Trp73 to Cys (LiaRW73C). We have determined the structure of the activated E. faecium LiaR protein at 3.2 Å resolution and, in combination with solution studies, show that the activation of LiaR induces the formation of a LiaR dimer that increases LiaR affinity at least 40-fold for the extended regulatory regions upstream of the liaFSR and liaXYZ operons. In vitro, LiaRW73C induces phosphorylation-independent dimerization of LiaR and provides a biochemical basis for non-susceptibility to DAP by the upregulation of the LiaFSR regulon. A comparison of the E. faecalis LiaR, E. faecium LiaR, and the LiaR homolog from Staphylococcus aureus (VraR) and the mutations associated with DAP resistance suggests that physicochemical properties such as oligomerization state and DNA specificity, although tuned to the biology of each organism, share some features that could be targeted for new antimicrobials
Advances in Alfalfa Variety Development and Testing
Alfalfa (Medicago sativa) is historically the highest yielding, highest quality forage legume grown in Kentucky. It forms the basis of Kentucky\u27s cash hay enterprise and is an important component in dairy, horse, beef and sheep diets. Over 300,000 acres of alfalfa are grown annually in Kentucky, with state yields averaging between 3 and 4 tons per acre.
The development and testing of alfalfa varieties is a dynamic process that impacts all Kentucky farmers. The Kentucky Alfalfa Variety Testing program was re-started in 1990 and is carried out through the efforts of several people, including Leonard Lauriault, Linda Brown (Western Kentucky University), Garry Lacefield, Paul Vincelli, and John Parr. Alfalfa varieties are being studied for yield in 6 plot studies over 3 locations (Lexington, Bowling Green, and Princeton). Other research being conducted include the effect of aphanomyces root rot on variety yield and persistence and the effect of variety on forage quality
Spectropolarimetry of SN 2011dh in M51: geometric insights on a Type IIb supernova progenitor and explosion
We present seven epochs of spectropolarimetry of the Type IIb supernova (SN)
2011dh in M51, spanning 86 days of its evolution. The first epoch was obtained
9 days after the explosion, when the photosphere was still in the depleted
hydrogen layer of the stripped-envelope progenitor. Continuum polarization is
securely detected at the level of P~0.5% through day 14 and appears to diminish
by day 30, which is different from the prevailing trends suggested by studies
of other core-collapse SNe. Time-variable modulations in P and position angle
are detected across P-Cygni line features. H-alpha and HeI polarization peak
after 30 days and exhibit position angles roughly aligned with the earlier
continuum, while OI and CaII appear to be geometrically distinct. We discuss
several possibilities to explain the evolution of the continuum and line
polarization, including the potential effects of a tidally deformed progenitor
star, aspherical radioactive heating by fast-rising plumes of Ni-56 from the
core, oblique shock breakout, or scattering by circumstellar material. While
these possibilities are plausible and guided by theoretical expectations, they
are not unique solutions to the data. The construction of more detailed
hydrodynamic and radiative-transfer models that incorporate complex aspherical
geometries will be required to further elucidate the nature of the polarized
radiation from SN 2011dh and other Type IIb supernovae.Comment: Post-proof edit. Accepted to MNRAS 2015 Aug 1
Multi-Epoch Spectropolarimetry for a Sample of Type IIn Supernovae: Persistent Asymmetry in Dusty Circumstellar Material
We present multi-epoch spectropolarimetry and spectra for a sample of 14 Type
IIn supernovae (SNe IIn). We find that after correcting for likely interstellar
polarization, SNe IIn commonly show intrinsic continuum polarization of 1--3%
at the time of peak optical luminosity, although a few show weaker or
negligible polarization. While some SNe IIn have even stronger polarization at
early times, their polarization tends to drop smoothly over several hundred
days after peak. We find a tendency for the intrinsic polarization to be
stronger at bluer wavelengths, especially at early times. While polarization
from an electron scattering region is expected to be grey, scattering of SN
light by dusty circumstellar material (CSM) may induce such a
wavelength-dependent polarization. For most SNe IIn, changes in polarization
degree and wavelength dependence are not accompanied by changes in the position
angle, requiring that asymmetric pre-SN mass loss had a persistent geometry.
While 2--3% polarization is typical, about 30% of SNe IIn have very low or
undetected polarization. Under the simplifying assumption that all SN IIn
progenitors have axisymmetric CSM (i.e. disk/torus/bipolar), then the
distribution of polarization values we observe is consistent with similarly
asymmetric CSM seen from a distribution of random viewing angles. This
asymmetry has very important implications for understanding the origin of
pre-SN mass loss in SNe IIn, suggesting that it was shaped by binary
interaction.Comment: 76 pages, 54 figures (13 in main text, 41 in appendix A
SN2012ab: A Peculiar Type IIn Supernova with Aspherical Circumstellar Material
We present photometry, spectra, and spectropolarimetry of supernova (SN)
2012ab, mostly obtained over the course of days after discovery. SN
2012ab was a Type IIn (SN IIn) event discovered near the nucleus of spiral
galaxy 2MASXJ12224762+0536247. While its light curve resembles that of SN
1998S, its spectral evolution does not. We see indications of CSM interaction
in the strong intermediate-width emission features, the high luminosity (peak
at absolute magnitude ), and the lack of broad absorption features in
the spectrum. The H emission undergoes a peculiar transition. At early
times it shows a broad blue emission wing out to km
and a truncated red wing. Then at late times (
100days) it shows a truncated blue wing and a very broad red emission wing
out to roughly km . This late-time broad red wing
probably arises in the reverse shock. Spectra also show an asymmetric
intermediate-width H component with stronger emission on the red side
at late times. The evolution of the asymmetric profiles requires a density
structure in the distant CSM that is highly aspherical. Our spectropolarimetric
data also suggest asphericity with a strong continuum polarization of % and depolarization in the H line, indicating asphericity in the
CSM at a level comparable to that in other SNe IIn. We estimate a mass-loss
rate of for km extending back at least 75yr prior to the
SN. The strong departure from axisymmetry in the CSM of SN 2012ab may suggest
that the progenitor was an eccentric binary system undergoing eruptive mass
loss.Comment: 18 pages, 12 figure
Potent and selective inhibition of SH3 domains with dirhodium metalloinhibitors
Src-family kinases (SFKs) play important roles in human biology and are key drug targets as well. However, achieving selective inhibition of individual Src-family kinases is challenging due to the high similarity within the protein family. We describe rhodium(II) conjugates that deliver both potent and selective inhibition of Src-family SH3 domains. Rhodium(II) conjugates offer dramatic affinity enhancements due to interactions with specific and unique Lewis-basic histidine residues near the SH3 binding interface, allowing predictable, structure-guided inhibition of SH3 targets that are recalcitrant to traditional inhibitors. In one example, a simple metallopeptide binds the Lyn SH3 domain with 6 nM affinity and exhibits functional activation of Lyn kinase under biologically relevant concentrations (EC50 ∼ 200 nM)
Influence of a Cyclonic Eddy on Microheterotroph Biomass and Carbon Export in the Lee of Hawaii
[1] A multi‐platform sampling strategy was used to investigate carbon cycling in a cold‐core eddy that formed in the lee of Hawaii during September 2000. Microheterotroph biomass and 234Th‐derived carbon export rates within the eddy were 2 to 3 times higher than those observed for adjacent waters. If this eddy is representative of other cyclonic eddies that are frequently formed in the lee of Hawaii, then eddy activity may significantly enhance the areal efficiency of the biological pump and facilitate the transfer of organic carbon to organisms inhabiting the mesopelagic and abyssal‐benthic zones of this subtropical ecosystem
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