36 research outputs found
Structural changes in activated wood-based carbons: correlation between specific surface area and localization of molecular-sized pores
Samples of maple were pyrolyzed and subsequently activated by carbon dioxide at different temperatures for various dwell times. The changes in wood structure were characterized by nitrogen adsorption isotherms, transmission electron microscopy (TEM) with selected-area electron diffraction (SAED), and scanning electron microscopy (SEM). Increasing pyrolysis temperatures promoted increased crystallization of graphitic wood components and mineral-like phases. The average pore diameter derived from nitrogen adsorption isotherms approximately correlated with the results obtained by high-resolution SEM and TEM. The highest surface area was found for samples containing considerable amounts of nanoperforated pit membranes located in intervascular pitting. High-resolution TEM examinations of membrane regions showed foam-like clusters with an average size of 1.7nm, which are attributed to the selective influence of CO2 activation on pyrolyzed cellulose and ligni
Lingunite-a high-pressure plagioclase polymorph at mineral interfaces in doleritic rock of the Lockne impact structure (Sweden)
Lingunite nanocrystals and amorphous plagioclase (maskelynite) are identified at the contacts
between augite and labradorite wedge-shaped interfaces in the doleritic rocks of the Lockne impact
structure in Sweden. The occurrence of lingunite suggests that the local pressure was above 19 GPa
and the local temperature overwhelmed 1000 °C. These values are up to 10 times higher than previous
values estimated numerically for bulk pressure and temperature. High shock-induced temperatures
are manifested by maskelynite injections into microfractures in augite located next to the wedges.
We discuss a possible model of shock heterogeneity at mineral interfaces, which may lead to longer
duration of the same shock pressure and a concentration of high temperature thus triggering the
kinetics of labradorite transformation into lingunite and maskelynite
On the multi-orbital band structure and itinerant magnetism of iron-based superconductors
This paper explains the multi-orbital band structures and itinerant magnetism
of the iron-pnictide and chalcogenides. We first describe the generic band
structure of an isolated FeAs layer. Use of its Abelian glide-mirror group
allows us to reduce the primitive cell to one FeAs unit. From
density-functional theory, we generate the set of eight Fe and As
localized Wannier functions for LaOFeAs and their tight-binding (TB)
Hamiltonian, . We discuss the topology of the bands, i.e. allowed and
avoided crossings, the origin of the d6 pseudogap, as well as the role of the
As orbitals and the elongation of the FeAs tetrahedron. We then
couple the layers, mainly via interlayer hopping between As orbitals,
and give the formalism for simple and body-centered tetragonal stackings. This
allows us to explain the material-specific 3D band structures. Due to the high
symmetry, several level inversions take place as functions of or
pressure, resulting in linear band dispersions (Dirac cones). The underlying
symmetry elements are, however, easily broken, so that the Dirac points are not
protected, nor pinned to the Fermi level. From the paramagnetic TB Hamiltonian,
we form the band structures for spin spirals with wavevector by coupling
and . The band structure for stripe order is studied as a
function of the exchange potential, , using Stoner theory. Gapping of
the Fermi surface (FS) for small requires matching of FS dimensions
(nesting) and -orbital characters. The origin of the propeller-shaped FS is
explained. Finally, we express the magnetic energy as the sum over
band-structure energies, which enables us to understand to what extent the
magnetic energies might be described by a Heisenberg Hamiltonian, and the
interplay between the magnetic moment and the elongation of the FeAs4
tetrahedron
Induction of antitumor immunity through xenoplacental immunization
Historically cancer vaccines have yielded suboptimal clinical results. We have developed a novel strategy for eliciting antitumor immunity based upon homology between neoplastic tissue and the developing placenta. Placenta formation shares several key processes with neoplasia, namely: angiogenesis, activation of matrix metalloproteases, and active suppression of immune function. Immune responses against xenoantigens are well known to break self-tolerance. Utilizing xenogeneic placental protein extracts as a vaccine, we have successfully induced anti-tumor immunity against B16 melanoma in C57/BL6 mice, whereas control xenogeneic extracts and B16 tumor extracts where ineffective, or actually promoted tumor growth, respectively. Furthermore, dendritic cells were able to prime tumor immunity when pulsed with the placental xenoantigens. While vaccination-induced tumor regression was abolished in mice depleted of CD4 T cells, both CD4 and CD8 cells were needed to adoptively transfer immunity to naïve mice. Supporting the role of CD8 cells in controlling tumor growth are findings that only freshly isolated CD8 cells from immunized mice were capable of inducing tumor cell caspases-3 activation ex vivo. These data suggest feasibility of using xenogeneic placental preparations as a multivalent vaccine potently targeting not just tumor antigens, but processes that are essential for tumor maintenance of malignant potential
Inter-site pair superconductivity: origins and recent validation experiments
The challenge of understanding high-temperature superconductivity has led to
a plethora of ideas, but 30 years after its discovery in cuprates, very few
have achieved convincing experimental validation. While Hubbard and t-J models
were given a lot of attention, a number of recent experiments appear to give
decisive support to the model of real-space inter-site pairing and percolative
superconductivity in cuprates. Systematic measurements of the doping dependence
of the superfluid density show a linear dependence on superfluid density -
rather than doping - over the entire phase diagram, in accordance with the
model's predictions. The doping-dependence of the anomalous lattice dynamics of
in-plane Cu-O mode vibrations observed by inelastic neutron scattering, gives
remarkable reciprocal space signature of the inter-site pairing interaction
whose doping dependence closely follows the predicted pair density.
Symmetry-specific time-domain spectroscopy shows carrier localization, polaron
formation, pairing and superconductivity to be distinct processes occurring on
distinct timescales throughout the entire superconducting phase diagram. The
three diverse experimental results confirm non-trivial predictions made more
than a decade ago by the inter-site pairing model in the cuprates, remarkably
also confirming some of the fundamental notions mentioned in the seminal paper
on the discovery of high-temperature superconductivity in cuprates.Comment: Dedicated to Prof. K. A. Mueller on the Occasion of his 90th Birthda
Investigating the role of TTP in mRNA decay and pre-mRNA processing
The AU-rich element (ARE) is a cis-encoded determinant within mRNA 3' untranslated regions (UTRs) that contributes to mRNA translation and stability in the cell. Tristetraprolin (TTP) is an RNA binding protein that specifically binds to mRNAs containing AREs and activates their rapid decay. TTP is rapidly activated following external stimulus and modulates the gene expression program of the responding cell. To better understand TTP- mediated mRNA decay activity, I identified the RNA binding protein hnRNP F as an RNA-independent interactor of TTP. I further characterized this interaction and observed that hnRNP F stimulated the decay of a subset of TTP-associated mRNAs, thus implicating hnRNP F in mRNA decay activated by TTP. Several possible mechanisms were tested but it remains to be determined how hnRNP F stimulates the decay of TTP-associated mRNAs. In addition to mRNA degradation, TTP appears to regulate gene expression through non-mRNA decay activities. I observed that TTP expression stimulated the 3' end processing of ARE-containing reporter mRNAs, leading to alternatively polyadenylated mRNAs with shortened 3' UTRs. This resulted in stabilization and loss of regulation of these mRNAs by TTP. The 3' end processing required an ARE and an upstream polyadenylation signal, and RNA binding of TTP was necessary but not sufficient for this activity. Thus, TTP appears to be a multifunctional protein, which in addition to mRNA decay activity promotes the 3' end processing of mRNAs, altering the 3' UTR composition and mRNA regulation in cell
Formation of structure and properties of dielectric diamond-charged ceramics of the basis of aggregated powders
The aim of the work is to reveal salient features and to determine mechanisms of influence of diamond synthetic powders submicrometer aggregation upon structure and properties of diamond-charged ceramics. Ordered powder aggregate formation effect has been revealed for the first time and phenomenological description of this effect has been offered. An empirical problem set up of a diamond particle has been developed that allow to rationalize both dispersive interaction between particles and diamond-charged ceramics structure formation. Diamond particles optimal size for homogeneous diamond-charged ceramics construction has been developed theoretically and confirmed experimentally. Potentialities in principal to manufacture high-stability chip resistors on the basis of diamond-charged ceramics has been shown. A technique for high-stability chip resistors production with the usage of laser technology has been promoted. The introduced method allowed to improve a unit of the new secondary power sourceAvailable from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio