758 research outputs found
Stabilization of porous glass reverse-osmosis membranes
Application of porous glass in form of capillary tubes for low capacity ion exchange in hyperfiltration experiments is discussed. Efficiency of desalination by process of reverse osmosis is described. Stabilization of porous glass membrane by presence of aluminum chloride is analyzed
Propagation and Ghosts in the Classical Kagome Antiferromagnet
We investigate the classical spin dynamics of the kagome antiferromagnet by
combining Monte Carlo and spin dynamics simulations. We show that this model
has two distinct low temperature dynamical regimes, both sustaining propagative
modes. The expected gauge invariance type of the low energy low temperature out
of plane excitations is also evidenced in the non linear regime. A detailed
analysis of the excitations allows to identify ghosts in the dynamical
structure factor, i.e propagating excitations with a strongly reduced spectral
weight. We argue that these dynamical extinction rules are of geometrical
origin.Comment: 4+ pages, 4 figures. Accepted for publication in the Physical Review
Letter
Use of glow discharge in fluidized beds
Static charges and agglomerization of particles in a fluidized bed systems are minimized by maintaining in at least part of the bed a radio frequency glow discharge. This approach is eminently suitable for processes in which the conventional charge removing agents, i.e., moisture or conductive particle coatings, cannot be used. The technique is applied here to the disproportionation of calcium peroxide diperoxyhydrate to yield calcium superoxide, an exceptionally water and heat sensitive reaction
Mineral separation and recycle in a Controlled Ecological Life Support System (CELSS)
The background of the mineral nutrition needs of plants are examined along with the applicability of mineral control and separation to a controlled ecological life support system (CELSS). Steps that may be taken in a program to analytically define and experimentally test key mineral control concepts in the nutritional and waste processing loops of a CELSS are delineated
Process for the preparation of calcium superoxide
Calcium superoxide is prepared in high yields by spreading a quantity of calcium peroxide diperoxyhydrate on the surface of a container, positioning said container in a vacuum chamber on a support structure through which a coolant fluid can be circulated, partially evacuating said vacuum chamber, allowing the temperature of the diperoxyhydrate to reach the range of about 0 to about 40 C; maintaining the temperature selected for a period of time sufficient to complete the disproproriation of the diperoxyhydrate to calcium superoxide, calcium hydroxide, oxygen, and water; constantly and systematically removing the water as it is formed by sweeping the reacting material with a current of dry inert gas and/or by condensation of said water on a cold surface; backfilling the chamber with a dry inert gas; and finally, recovering the calcium superoxide produced
Magnetic excitations in a new anisotropic Kagom\'{e} antiferromagnet
The Nd-langasite compound contains planes of magnetic Nd3+ ions on a lattice
topologically equivalent to a kagom\'{e} net. The magnetic susceptibility does
not reveal any signature of long-range ordering down to 2 K but rather a
correlated paramagnetism with significant antiferromagnetic interactions
between the Nd and a single-ion anisotropy due to crystal field effect.
Inelastic neutron scattering on Nd-langasite powder and single-crystal allowed
to probe its very peculiar low temperature dynamical magnetic correlations.
They present unusual dispersive features and are broadly localized in
wave-vector Q revealing a structure factor associated to characteristics short
range-correlations between the magnetic atoms. From comparison with theoretical
calculations, these results are interpreted as a possible experimental
observation of a spin liquid state in an anisotropic kagom\'{e}
antiferromagnet.Comment: to appear in Physica
Inhomogeneous magnetism in the doped kagome lattice of LaCuO2.66
The hole-doped kagome lattice of Cu2+ ions in LaCuO2.66 was investigated by
nuclear quadrupole resonance (NQR), electron spin resonance (ESR), electrical
resistivity, bulk magnetization and specific heat measurements. For
temperatures above ~180 K, the spin and charge properties show an activated
behavior suggestive of a narrow-gap semiconductor. At lower temperatures, the
results indicate an insulating ground state which may or may not be charge
ordered. While the frustrated spins in remaining patches of the original kagome
lattice might not be directly detected here, the observation of coexisting
non-magnetic sites, free spins and frozen moments reveals an intrinsically
inhomogeneous magnetism. Numerical simulations of a 1/3-diluted kagome lattice
rationalize this magnetic state in terms of a heterogeneous distribution of
cluster sizes and morphologies near the site-percolation threshold
Single domain magnetic helicity and triangular chirality in structurally enantiopure Ba3NbFe3Si2O14
A novel doubly chiral magnetic order is found out in the structurally chiral
langasite compound BaNbFeSiO. The magnetic moments are
distributed over planar frustrated triangular lattices of triangle units. On
each of these they form the same triangular configuration. This ferro-chiral
arrangement is helically modulated from plane to plane. Unpolarized neutron
scattering on a single crystal associated with spherical neutron polarimetry
proved that a single triangular chirality together with a single helicity is
stabilized in an enantiopure crystal. A mean field analysis allows discerning
the relevance on this selection of a twist in the plane to plane
supersuperexchange paths
Crystal Symmetry Lowering in Chiral Multiferroic BaTaFeSiO observed by X-Ray Magnetic Scattering
Chiral multiferroic langasites have attracted attention due to their
doubly-chiral magnetic ground state within an enantiomorphic crystal. We report
on a detailed resonant soft X-ray diffraction study of the multiferroic
BaTaFeSiO at the Fe and oxygen edges. Below
() we observe the satellite reflections ,
, and where . The dependence of the scattering intensity on X-ray polarization and
azimuthal angle indicate that the odd harmonics are dominated by the
out-of-plane (-axis) magnetic dipole while the
originates from the electron density distortions accompanying magnetic order.
We observe dissimilar energy dependences of the diffraction intensity of the
purely magnetic odd-harmonic satellites at the Fe edge. Utilizing
first-principles calculations, we show that this is a consequence of the loss
of threefold crystal symmetry in the multiferroic phase
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