9,515 research outputs found
Phonon Properties of Knbo3 and Ktao3 from First-Principles Calculations
The frequencies of transverse-optical phonons in KNbO and
KTaO are calculated in the frozen-phonon scheme making use of the
full-potential linearized muffin-tin orbital method. The calculated frequencies
in the cubic phase of KNbO and in the tetragonal ferroelectric phase are in
good agreement with experimental data. For KTaO, the effect of lattice
volume was found to be substantial on the frequency of the soft mode, but
rather small on the relative displacement patterns of atoms in all three modes
of the symmetry. The TO frequencies in KTaO are found to be of the
order of, but somehow higher than, the corresponding frequencies in cubic
KNbO.Comment: 8 pages + 1 LaTeX figure, Revtex 3.0, SISSA-CM-94-00
Some closure operations in Zariski-Riemann spaces of valuation domains: a survey
In this survey we present several results concerning various topologies that
were introduced in recent years on spaces of valuation domains
Evidences for Paleo-Gas Hydrate Occurrence: What We Can Infer for the Miocene of the Northern Apennines (Italy)
The occurrence of seep-carbonates associated with shallow gas hydrates is increasingly
documented in modern continental margins but in fossil sediments the recognition of gas hydrates
is still challenging for the lack of unequivocal proxies. Here, we combined multiple field and
geochemical indicators for paleo-gas hydrate occurrence based on present-day analogues to
investigate fossil seeps located in the northern Apennines. We recognized clathrite-like structures such
as thin-layered, spongy and vuggy textures and microbreccias. Non-gravitational cementation fabrics
and pinch-out terminations in cavities within the seep-carbonate deposits are ascribed to irregularly
oriented dissociation of gas hydrates. Additional evidences for paleo-gas hydrates are provided by
the large dimensions of seep-carbonate masses and by the association with sedimentary instability
in the host sediments. We report heavy oxygen isotopic values in the examined seep-carbonates up
to +6h that are indicative of a contribution of isotopically heavier fluids released by gas hydrate
decomposition. The calculation of the stability field of methane hydrates for the northern Apennine
wedge-foredeep system during the Miocene indicated the potential occurrence of shallow gas
hydrates in the upper few tens of meters of sedimentary column
New distinguished classes of spectral spaces: a survey
In the present survey paper, we present several new classes of Hochster's
spectral spaces "occurring in nature", actually in multiplicative ideal theory,
and not linked to or realized in an explicit way by prime spectra of rings. The
general setting is the space of the semistar operations (of finite type),
endowed with a Zariski-like topology, which turns out to be a natural
topological extension of the space of the overrings of an integral domain,
endowed with a topology introduced by Zariski. One of the key tool is a recent
characterization of spectral spaces, based on the ultrafilter topology, given
in a paper by C. Finocchiaro in Comm. Algebra 2014. Several applications are
also discussed
T-PHOT version 2.0: improved algorithms for background subtraction, local convolution, kernel registration, and new options
We present the new release v2.0 of T-PHOT, a publicly available software
package developed to perform PSF-matched, prior-based, multiwavelength
deconfusion photometry of extragalactic fields. New features included in the
code are presented and discussed: background estimation, fitting using position
dependent kernels, flux prioring, diagnostical statistics on the residual
image, exclusion of selected sources from the model and residual images,
individual registration of fitted objects. These new options improve on the
performance of the code, allowing for more accurate results and providing
useful aids for diagnostics.Comment: 7 pages, 8 figure
Thermodynamic Scaling of the Viscosity of Van Der Waals, H-Bonded, and Ionic Liquids
Viscosities and their temperature, T, and volume, V, dependences are reported
for 7 molecular liquids and polymers. In combination with literature viscosity
data for 5 other liquids, we show that the superpositioning of relaxation times
for various glass-forming materials when expressed as a function of TV^g, where
the exponent g is a material constant, can be extended to the viscosity. The
latter is usually measured to higher temperatures than the corresponding
relaxation times, demonstrating the validity of the thermodynamic scaling
throughout the supercooled and higher T regimes. The value of g for a given
liquid principally reflects the magnitude of the intermolecular forces (e.g.,
steepness of the repulsive potential); thus, we find decreasing g in going from
van der Waals fluids to ionic liquids. For strongly H-bonded materials, such as
low molecular weight polypropylene glycol and water, the superpositioning
fails, due to the non-trivial change of chemical structure (degree of
H-bonding) with thermodynamic conditions.Comment: 16 pages 7 figure
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