579 research outputs found
Activated Carbon Produced from Agricultural Residues
A process for producing activated carbon from agricultural residues by heating the residues to a temperature in the range of about 250° C. to about 550° C. to volatilize organic compounds in the residues and to carbonize the residues and further heating to activate the carbonized residues. Activated carbon produced from agricultural residues
A Magnetic Transition Probed by the Ce Ion in Square-Lattice Antiferromagnet CeMnAsO
We examined the magnetic properties of the square-lattice antiferromagnets
CeMnAsO and LaMnAsO and their solid solutions La1-xCexMnAsO by resistivity,
magnetic susceptibility, and heat capacity measurements below room temperature.
A first-order phase transition is observed at 34.1 K, below which the
ground-state doublet of the Ce ion splits by 3.53 meV. It is likely that Mn
moments already ordered above room temperature are reoriented at the
transition, as reported for related compounds, such as NdMnAsO and PrMnSbO.
This transition generates a large internal magnetic field at the Ce site in
spite of the fact that simple Heisenberg interactions should be cancelled out
at the Ce site owing to geometrical frustration. The transition takes place at
nearly the same temperature with the substitution of La for Ce up to 90%. The
Ce moment does not undergo long-range order by itself, but is parasitically
induced at the transition, serving as a good probe for detecting the magnetism
of Mn spins in a square lattice.Comment: 11 pages, 5 figures, to be published in J. Phys. Soc. Jp
Lattice collapse and quenching of magnetism in CaFe2As2 under pressure: A single crystal neutron and x-ray diffraction investigation
Single crystal neutron and high-energy x-ray diffraction have identified the
phase lines corresponding to transitions between the ambient-pressure
tetragonal (T), the antiferromagnetic orthorhombic (O) and the non-magnetic
collapsed tetragonal (cT) phases of CaFe2As2. We find no evidence of additional
structures for pressures up to 2.5 GPa (at 300 K). Both the T-cT and O-cT
transitions exhibit significant hysteresis effects and we demonstrate that
coexistence of the O and cT phases can occur if a non-hydrostatic component of
pressure is present. Measurements of the magnetic diffraction peaks show no
change in the magnetic structure or ordered moment as a function of pressure in
the O phase and we find no evidence of magnetic ordering in the cT phase. Band
structure calculations show that the transition results in a strong decrease of
the iron 3d density of states at the Fermi energy, consistent with a loss of
the magnetic moment.Comment: List of authors in metadata and typos in labeling of inset in Fig.
1(a) corrected. One ref. added. No other change
Solution of the Kwiecinski evolution equations for unintegrated parton distributions using the Mellin transform
The Kwiecinski equations for the QCD evolution of the unintegrated parton
distributions in the transverse-coordinate space (b) are analyzed with the help
of the Mellin-transform method. The equations are solved numerically in the
general case, as well as in a small-b expansion which converges fast for b
Lambda_QCD sufficiently small. We also discuss the asymptotic limit of large bQ
and show that the distributions generated by the evolution decrease with b
according to a power law. Numerical results are presented for the pion
distributions with a simple valence-like initial condition at the low scale,
following from chiral large-N_c quark models. We use two models: the Spectral
Quark Model and the Nambu--Jona-Lasinio model. Formal aspects of the equations,
such as the analytic form of the b-dependent anomalous dimensions, their
analytic structure, as well as the limits of unintegrated parton densities at x
-> 0, x -> 1, and at large b, are discussed in detail. The effect of spreading
of the transverse momentum with the increasing scale is confirmed, with
growing asymptotically as Q^2 alpha(Q^2). Approximate formulas for
for each parton species is given, which may be used in practical
applications.Comment: 18 pages, 6 figures, RevTe
Comparison of -Factorization Approach and QCD Parton Model for Charm and Beauty Hadroproduction
We compare the numerical predictions for heavy quark production in high
energy hadron collisions of the conventional QCD parton model and the
-factorization approach (semihard theory). The total production cross
sections, one-particle rapidity and distributions as well as two-particle
correlations are considered. The difference in the predictions of the two
approaches is not very large, while the shapes of the distributions are
slightly different.Comment: 16 pages, LaTeX, + 16 PostScript figure
Heavy Quark Hadroproduction in -Factorization Approach with Unintegrated Gluon Distributions
We consider the processes of compare the heavy quark production using the
unintegrated gluon distributions. The numerical predictions for high energy
nucleon-nucleon and photon-nucleon collisions of the -factorization
approach (semihard theory) are compared with the experimental data from
Tevatron-collider and HERA. The total production cross sections and
distributions are considered and they are in reasonable agreement with the data
for rather value of QCD scale.Comment: 21 pages, 10 figures, references adde
Structural and magnetic phase diagram of CeFeAsO1-xFx and its relationship to high-temperature superconductivity
We use neutron scattering to study the structural and magnetic phase
transitions in the iron pnictides CeFeAsO1-xFx as the system is tuned from a
semimetal to a high-transition-temperature (high-Tc) superconductor through
Fluorine (F) doping x. In the undoped state, CeFeAsO develops a structural
lattice distortion followed by a stripe like commensurate antiferromagnetic
order with decreasing temperature. With increasing Fluorine doping, the
structural phase transition decreases gradually while the antiferromagnetic
order is suppressed before the appearance of superconductivity, resulting an
electronic phase diagram remarkably similar to that of the high-Tc copper
oxides. Comparison of the structural evolution of CeFeAsO1-xFx with other
Fe-based superconductors reveals that the effective electronic band width
decreases systematically for materials with higher Tc. The results suggest that
electron correlation effects are important for the mechanism of high-Tc
superconductivity in these Fe pnictides.Comment: 19 pages, 5 figure
Pressure versus concentration tuning of the superconductivity in Ba(Fe(1-x)Cox)2As2
In the iron arsenide compound BaFe2As2, superconductivity can be induced
either by a variation of its chemical composition, e.g., by replacing Fe with
Co, or by a reduction of the unit-cell volume through the application of
hydrostatic pressure p. In contrast to chemical substitutions, pressure is
expected to introduce no additional disorder into the lattice. We compare the
two routes to superconductivity by measuring the p dependence of the
superconducting transition temperature Tc of Ba(Fe(1-x)Cox)2As2 single crystals
with different Co content x. We find that Tc(p) of underdoped and overdoped
samples increases and decreases, respectively, tracking quantitatively the
Tc(x) dependence. To clarify to which extent the superconductivity relies on
distinct structural features we analyze the crystal structure as a function of
x and compare the results with that of BaFe2As2 under pressure.Comment: 14 pages, 4 figures, to be published in JPSJ Vol. 79 No. 12. The
copyright is held by The Physical Society of Japa
Lipoprotein lipase is active as a monomer
Lipoprotein lipase (LPL), the enzyme that hydrolyzes triglycerides in plasma lipoproteins, is assumed to be active only as a homodimer. In support of this idea, several groups have reported that the size of LPL, as measured by density gradient ultracentrifugation, is ∼110 kDa, twice the size of LPL monomers (∼55 kDa). Of note, however, in those studies the LPL had been incubated with heparin, a polyanionic substance that binds and stabilizes LPL. Here we revisited the assumption that LPL is active only as a homodimer. When freshly secreted human LPL (or purified preparations of LPL) was subjected to density gradient ultracentrifugation (in the absence of heparin), LPL mass and activity peaks exhibited the size expected of monomers (near the 66-kDa albumin standard). GPIHBP1-bound LPL also exhibited the size expected for a monomer. In the presence of heparin, LPL size increased, overlapping with a 97.2-kDa standard. We also used density gradient ultracentrifugation to characterize the LPL within the high-salt and low-salt peaks from a heparin-Sepharose column. The catalytically active LPL within the high-salt peak exhibited the size of monomers, whereas most of the inactive LPL in the low-salt peak was at the bottom of the tube (in aggregates). Consistent with those findings, the LPL in the low-salt peak, but not that in the high-salt peak, was easily detectable with single mAb sandwich ELISAs, in which LPL is captured and detected with the same antibody. We conclude that catalytically active LPL can exist in a monomeric state
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