3,014 research outputs found
Colony-stimulating factor-1 suppresses responses to CpG DNA and expression of toll-like receptor 9 but enhances responses to lipopolysaccharide in murine macrophages
Fermi surface and quasiparticle dynamics of Na(x)CoO2 {x=0.7} investigated by Angle-Resolved Photoemission Spectroscopy
We present an angle-resolved photoemission study of Na0.7CoO2, the host
cobaltate of the NaxCoO2.yH2O series. Our results show a large hexagonal-like
hole-type Fermi surface, an extremely narrow strongly renormalized
quasiparticle band and a small Fermi velocity. Along the Gamma to M high
symmetry line, the quasiparticle band crosses the Fermi level from M toward
Gamma consistent with a negative sign of effective single-particle hopping (t
): t is estimated to be about 8 meV which is on the order of exchange coupling
J in this system. This suggests that t ~ J ~ 10 meV is an important energy
scale in the system. Quasiparticles are well defined only in the T-linear
resistivity regime. Small single particle hopping and unconventional
quasiparticle dynamics may have implications for understanding the unusual
behavior of this new class of compounds.Comment: Revised text, Added Figs, Submitted to PR
Structure and Dynamics of Superconducting NaxCoO(2) Hydrate and Its Unhydrated Analog
Neutron scattering has been used to investigate the crystal structure and
lattice dynamics of superconducting Na0.3CoO2 1.4(H/D)2O, and the parent
Na0.3CoO2 material. The structure of Na0.3CoO2 consists of alternate layers of
CoO2 and Na and is the same as the structure at higher Na concentrations. For
the superconductor, the water forms two additional layers between the Na and
CoO2, increasing the c-axis lattice parameter of the hexagonal P63/mmc space
group from 11.16 A to 19.5 A. The Na ions are found to occupy a different
configuration from the parent compound, while the water forms a structure that
replicates the structure of ice. Both types of sites are only partially
occupied. The CoO2 layer in these structures is robust, on the other hand, and
we find a strong inverse correlation between the CoO2 layer thickness and the
superconducting transition temperature (TC increases with decreasing
thickness). The phonon density-of-states for Na0.3CoO2 exhibits distinct
acoustic and optic bands, with a high-energy cutoff of ~100 meV. The lattice
dynamical scattering for the superconductor is dominated by the hydrogen modes,
with librational and bending modes that are quite similar to ice, supporting
the structural model that the water intercalates and forms ice-like layers in
the superconductor.Comment: 14 pages, 7 figures, Phys. Rev. B (in press). Minor changes + two
figures removed as requested by refere
Effect of Condensed Tannin in Lotus Corniculatus and Lotus Pedunculatus on Digestion of Rubisco in the Rumen
The in vitro precipitation of ribulose-1,5-bisphosphate carboxylase (Rubisco) by condensed tannin (CT) extracted from Lotus corniculatus and Lotus pedunculatus and the effect of these CT on the in vitro rumen degradation of Rubisco was used to compare the reactivity of these CT. The chemical structure of CT from Lotus corniculatus was homogenous with epicatechin stereochemistry and mostly procyanidin units. The CT from Lotus pedunculatus was heterogenous with mostly prodelphinidin units. The amount of CT required to precipitate all the Rubisco when total soluble leaf protein was incubated with CT from Lotus corniculatus and Lotus pedunculatus was similar. Although CT from both species were able to reduce the in vitro degradation of Rubisco, CT from Lotus corniculatus was less effective than CT from Lotus pedunculatus at reducing this degradation
Large enhancement of the thermopower in NaCoO at high Na doping
Research on the oxide perovskites has uncovered electronic properties that
are strikingly enhanced compared with those in conventional metals. Examples
are the high critical temperatures of the cuprate superconductors and the
colossal magnetoresistance in the manganites. The conducting layered cobaltate
displays several interesting electronic phases as is varied
including water-induced superconductivity and an insulating state that is
destroyed by field. Initial measurements showed that, in the as-grown
composition, displays moderately large thermopower and
conductivity . However, the prospects for thermoelectric cooling
applications faded when the figure of merit was found to be small at this
composition (0.60.7). Here we report that, in the poorly-explored
high-doping region 0.75, undergoes an even steeper enhancement. At the
critical doping 0.85, (at 80 K) reaches values 40 times
larger than in the as-grown crystals. We discuss prospects for low-temperature
thermoelectric applications.Comment: 6 pages, 7 figure
Modelling upper respiratory viral load dynamics of SARS-CoV-2
Relationships between viral load, severity of illness, and transmissibility of virus, are fundamental to understanding pathogenesis and devising better therapeutic and prevention strategies for COVID-19. Here we present within-host modelling of viral load dynamics observed in the upper respiratory tract (URT), drawing upon 2172 serial measurements from 605 subjects, collected from 17 different studies. We developed a mechanistic model to describe viral load dynamics and host response, and contrast this with simpler mixed-effects regression analysis of peak viral load and its subsequent decline. We observed wide variation in URT viral load between individuals, over 5 orders of magnitude, at any given point in time since symptom onset. This variation was not explained by age, sex, or severity of illness, and these variables were not associated with the modelled early or late phases of immune-mediated control of viral load. We explored the application of the mechanistic model to identify measured immune responses associated with control of viral load. Neutralizing antibody correlated strongly with modelled immune-mediated control of viral load amongst subjects who produced neutralizing antibody. Our models can be used to identify host and viral factors which control URT viral load dynamics, informing future treatment and transmission blocking interventions
Coupling between electronic and structural degrees of freedom in the triangular lattice conductor NaxCoO2
The determination by powder neutron diffraction of the ambient temperature
crystal structures of compounds in the NaxCoO2 family, for 0.3 < x <= 1.0, is
reported. The structures consist of triangular CoO2 layers with Na ions
distributed in intervening charge reservoir layers. The shapes of the CoO6
octahedra that make up the CoO2 layers are found to be critically dependent on
the electron count and on the distribution of the Na ions in the intervening
layers, where two types of Na sites are available. Correlation of the shapes of
cobalt-oxygen octahedra, the Na ion positions, and the electronic phase diagram
in NaxCoO2 is made, showing how structural and electronic degrees of freedom
can be coupled in electrically conducting triangular lattice systems.Comment: 15 pages, 1 tables, 6 figures Submitted to Physical Review
Macrophages exposed continuously to lipopolysaccharide and other agonists that act via toll-like receptors exhibit a sustained and additive activation state
BACKGROUND: Macrophages sense microorganisms through activation of members of the Toll-like receptor family, which initiate signals linked to transcription of many inflammation associated genes. In this paper we examine whether the signal from Toll-like receptors [TLRs] is sustained for as long as the ligand is present, and whether responses to different TLR agonists are additive. RESULTS: RAW264 macrophage cells were doubly-transfected with reporter genes in which the IL-12p40, ELAM or IL-6 promoter controls firefly luciferase, and the human IL-1Ξ² promoter drives renilla luciferase. The resultant stable lines provide robust assays of macrophage activation by TLR stimuli including LPS [TLR4], lipopeptide [TLR2], and bacterial DNA [TLR9], with each promoter demonstrating its own intrinsic characteristics. With each of the promoters, luciferase activity was induced over an 8 hr period, and thereafter reached a new steady state. Elevated expression required the continued presence of agonist. Sustained responses to different classes of agonist were perfectly additive. This pattern was confirmed by measuring inducible cytokine production in the same cells. While homodimerization of TLR4 mediates responses to LPS, TLR2 appears to require heterodimerization with another receptor such as TLR6. Transient expression of constitutively active forms of TLR4 or TLR2 plus TLR6 stimulated IL-12 promoter activity. The effect of LPS, a TLR4 agonist, was additive with that of TLR2/6 but not TLR4, whilst that of lipopeptide, a TLR2 agonist, was additive with TLR4 but not TLR2/6. Actions of bacterial DNA were additive with either TLR4 or TLR2/6. CONCLUSIONS: These findings indicate that maximal activation by any one TLR pathway does not preclude further activation by another, suggesting that common downstream regulatory components are not limiting. Upon exposure to a TLR agonist, macrophages enter a state of sustained activation in which they continuously sense the presence of a microbial challenge
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Photoplethysmography for an independent measure of pulsatile pressure under controlled flow conditions
Noninvasive continuous blood pressure measurements are desirable for patients and clinicians. This work proposes and validates a method for transmural pressure measurement using photoplethysmography (PPG) in an in vitro setup that allows control of pressure and flow conditions. The optimum pulsatile volume measure is obtained by comparing parameters extracted from the photoplethysmographic signal (AC amplitude, normalized pulse volume (NPV) and adjusted pulse volume (APV)). Pulsatile volume can then provide pressure measurements using the exponential pressure-volume (P-V) relationship and validated using the gold standard catheter pressure measurement. Pressure, red (R) and infrared (IR) PPG signals were recorded continuously in two arterial models with different cross-sectional areas (Model 1 and Model 2) utilising a pulsatile pump. Flow rates were controlled by varying pumping frequencies at low and high stroke volumes. The optimum method for estimation of the pulsatile volume is through APV, which had a highly significant correlation (r (2)ββ=ββ0.99, pββ<ββ0.001) for Model 1 and (r (2)ββ=ββ0.98, pββ<ββ0.001) for Model 2. APV obtained a significantly better fit when compared to NPVIR (r (2)ββ=ββ0.73, zββ=ββ25.85, pββ<ββ0.001), NPVR (r (2)ββ=ββ0.95, zββ=ββ12.26, pββ<ββ0.001), IRAC (r (2)ββ=ββ0.52, zββ=ββ28.29, pββ<ββ0.0001) and RAC (r (2)ββ=ββ0.92, zββ=ββ15.27, pββ<ββ0.0001) in Model 1, and when compared to NPVIR (r (2)ββ=ββ0.92, zββ=ββ10.23, pββ<ββ0.0001), NPVR (r (2)ββ=ββ0.96, zββ=ββ5.08, pββ<ββ0.001) IRAC (r (2)ββ=ββ0.63, zββ=ββ22.47, pββ<ββ0.0001) and RAC (r (2)ββ=ββ0.92, zββ=ββ17.70, pββ<ββ0.0001) in Model 2. These preliminary findings suggest that APV could be used as a potential non-invasive continuous method of blood pressure measurement at different flow conditions
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