4,666 research outputs found
Effective One-Dimensional Coupling in the Highly-Frustrated Square-Lattice Itinerant Magnet CaCoAs
Inelastic neutron scattering measurements on the itinerant antiferromagnet
(AFM) CaCoAs at a temperature of 8 K reveal two
orthogonal planes of scattering perpendicular to the Co square lattice in
reciprocal space, demonstrating the presence of effective one-dimensional spin
interactions. These results are shown to arise from near-perfect bond
frustration within the - Heisenberg model on a square lattice with
ferromagnetic , and hence indicate that the extensive previous
experimental and theoretical study of the - Heisenberg model on
local-moment square spin lattices should be expanded to include itinerant spin
systems
Self-Assembly of \u3cem\u3eEscherichia coli\u3c/em\u3e MutL and Its Complexes with DNA
The Escherichia coli MutL protein regulates the activity of several enzymes, including MutS, MutH, and UvrD, during methyl-directed mismatch repair of DNA. We have investigated the self-association properties of MutL and its binding to DNA using analytical sedimentation velocity and equilibrium. Self-association of MutL is quite sensitive to solution conditions. At 25 °C in Tris at pH 8.3, MutL assembles into a heterogeneous mixture of large multimers. In the presence of potassium phosphate at pH 7.4, MutL forms primarily stable dimers, with the higher-order assembly states suppressed. The weight-average sedimentation coefficient of the MutL dimer in this buffer (s̅20,w) is equal to 5.20 ± 0.08 S, suggesting a highly asymmetric dimer (f/fo = 1.58 ± 0.02). Upon binding the nonhydrolyzable ATP analogue, AMPPNP/Mg2+, the MutL dimer becomes more compact (s̅20,w = 5.71 ± 0.08 S; f/fo = 1.45 ± 0.02), probably reflecting reorganization of the N-terminal ATPase domains. A MutL dimer binds to an 18 bp duplex with a 3′-(dT20) single-stranded flanking region, with apparent affinity in the micromolar range. AMPPNP binding to MutL increases its affinity for DNA by a factor of ∼10. These results indicate that the presence of phosphate minimizes further MutL oligomerization beyond a dimer and that differences in solution conditions likely explain apparent discrepancies in previous studies of MutL assembly
Spin Excitations in BaFe1.84Co0.16As2 Superconductor Observed by Inelastic Neutron Scattering
Superconductivity appears to compete against the spin-density-wave in Fe
pnictides. However, optimally cobalt doped samples show a quasi-two-dimensional
spin excitation centered at the (0.5, 0.5, L) wavevector, "the spin resonance
peak", that is strongly tied to the onset of superconductivity. By inelastic
neutron scattering on single crystals we show the similarities and differences
of the spin excitations in BaFe1.84Co0.16As2, with respect to the spin
excitations in the high-temperature superconducting cuprates. As in the
cuprates the resonance occurs as an enhancement to a part of the spin
excitation spectrum which extends to higher energy transfer and higher
temperature. However, unlike in the cuprates, the resonance peak in this
compound is asymmetric in energy.Comment: 12 pages, 6 figures; PACS # 74.70.-b, 74.20.Mn, 78.70.Nx, 74.25.Ha;
corrected discussion of figures in tex
The role of septal perforators and "myocardial bridging effect" in atherosclerotic plaque distribution in the coronary artery disease
The distribution of atherosclerotic plaque burden in the human coronary arteries is not uniform. Plaques are located mostly in the left anterior descending artery (LAD), then in the right coronary artery (RCA), circumflex branch (LCx) and the left main coronary artery (LM) in a decreasing order of frequency. In the LAD and LCx, plaques tend to cluster within the proximal segment, while in the RCA their distribution is more uniform. Several factors have been involved in this phenomenon, particularly flow patterns in the left and right coronary artery. Nevertheless, it does not explain the difference in lesion frequency between the LAD and the LCx as these are both parts of the left coronary artery. Branching points are considered to be the risk points of atherosclerosis. In the LCx, the number of side branches is lower than in the LAD or RCA and there are no septal perforators with intramuscular courses like in the proximal third of the LAD and the posterior descending artery (PDA). We hypothesized that septal branches generate disturbed flow in the LAD and PDA in a similar fashion to the myocardial bridge (myocardial bridging effect). This coronary architecture determines the non-uniform plaque distribution in coronary arteries and LAD predisposition to plaque formation
Selective preservation of protein kinase C-ζ in the chemoprevention of azoxymethane-induced colonic tumors by piroxicam
AbstractWhile nonsteroidal anti-inflammatory drugs have been shown to exert preventive effects against the development of colonic tumors in humans and in chemically-induced tumors in animal models, the mechanism(s) involved in this phenomenon is unclear. We have recently demonstrated that one such agent, piroxicam, when supplemented (75 ppm) in the diets of rats administered azoxymethane, reduced the incidence of rats bearing tumors. To date, the effects of piroxicam on protein kinase C, a family of serine/threonine kinases which may be intimately involved in the colonic malignant transformation process, have not been examined. It was, therefore, of interest to determine whether piroxicam altered the expression of one or more isoforms of this kinase in these tumors. The present studies demonstrate that dietary piroxicam selectively preserved the expression of protein kinase C-ζ in azoxymethane-induced tumors; suggesting that this is at least one mechanism involved in this agent's chemopreventive actions in this organ
Design and operating characteristic of a vacuum furnace for time-of-flight inelastic neutron scattering measurements
We present the design and operating characteristics of a vacuum furnace used for inelastic neutron scattering experiments on a time-of-flight chopper spectrometer. The device is an actively water cooled radiant heating furnace capable of performing experiments up to 1873 K. Inelastic neutron scattering studies performed with this furnace include studies of phonon dynamics and metallic liquids. We describe the design, control, characterization, and limitations of the equipment. Further, we provide comparisons of the neutron performance of our device with commercially available options. Finally we consider upgrade paths to improve performance and reliability
Assessment of adipokines, adenine nucleotides and uric acid in the dynamics of coronary intervention
Introduction: The association of vaspin
and visfatin, with a myocardial infarction is still
not fully understood. Reduced levels of adenine
nucleotides are hallmarks of chronic heart failure.
There is little data concerning the relationship
between these markers and their changes over time.
Material/Methods: The concentration of adenine
nucleotides, vaspin and visfatinwere assessed in 41
consecutive patients with acute myocardial infarction one
before (day I) and four days after (day IV) percutaneous
coronary intervention (PCI) and a control group.
Results: Visfatin concentrations were higher before and
after PCI vs. control (visfatin I: median 25.55, 20.12 - 30.69
ng/ml; visfatin IV: median 20.79, 16.89 - 25.61 ng/ml vs.
control: median 14.94, 10.66 - 25.25 ng/ml; p < 0.0001).
Vaspin concentrations were lower before and after PCI vs.
control (vaspin I: median 0.18, 0.11 - 0.44 ng/ml; vaspin IV:
median 0.24, 0.15 - 0.58 ng/ml vs. control: median 1.303,
1.13 - 2.26 ng/ml, p < 0.00001). Concentrations of visfatin, day I, correlated well to vaspin concentrations (r2 = 0.201,
p = 0.011). ATP levels were significantly lower in patients
vs. controls (day I: p = 0.00012; day IV: p = 0.0001).
Conclusions: Changes in the analyzed visfatin and vaspin
concentrations can be used as potential MI markers.
Visfatin serum concentration may be considered a
potential marker to differentiate MI over time
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