285 research outputs found
Ab initio study on the magneto-structural properties of MnAs
The magnetic and structural properties of MnAs are studied with ab initio
methods, and by mapping total energies onto a Heisenberg model. The stability
of the different phases is found to depend mainly on the volume and on the
amount of magnetic order, confirming previous experimental findings and
phenomenological models. It is generally found that for large lattice constants
the ferromagnetic state is favored, whereas for small lattice constants
different antiferromagnetic states can be stabilized. In the ferromagnetic
state the structure with minimal energy is always hexagonal, whereas it becomes
orthorhombically distorted if there is an antiferromagnetic component in the
hexagonal plane. For the paramagnetic state the stable cell is found to be
orthorhombic up to a critical lattice constant of about 3.7 Angstrom, above
which it remains hexagonal. This leads to the second order structural phase
transition between paramagnetic states at about 400 K, where the lattice
parameter increases above this critical value with rising temperature due to
the thermal expansion. For the paramagnetic state an analytic approximation for
the magnitude of the orthorhombic distortion as a function of the lattice
constant is given. Within the mean field approximation the dependence of the
Curie temperature on the volume and on the orthorhombic distortion is
calculated. For orthorhombically distorted cells the Curie temperature is much
smaller than for hexagonal cells. This is mainly due to the fact that some of
the exchange coupling constants in the hexagonal plane become negative for
distorted cells. With these results a description of the susceptibility as
function of temperature is given
Mechanochemical, Sonochemical and Hydrothermal Activation of Niobium Pentoxide and its Catalytic Properties
Modification of niobium pentoxide with different dispersity via mechanochemical, ultrasound, hydrothermal
and microwave treatments (MChT, UST, HTT, and MWT, respectively) has been studied. All types
of treatment do not change of phase composition but leads to improvement (at HTT and MWT) or, on contrary,
breaking of crystal structure (at MChT and UST) and variation of crystallite size and specific surface
area. UV-Vis measurements display increase of absorption in visible region. As a result, modified samples
show higher photocatalytic activity at degradation of rhodamine B under visible irradiation. Similarly, initial
and modified Nb2O5 samples are catalysts for mechanochtmical and sonochemical destruction of the
same dye.
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Study of Standpipe and Loop Seal Behavior in a Circulating Fluidized Bed for Geldart B Particles
The loop seal aeration effect on the supply side has been studied through small scale CFB experimentation. Parameters affected include inventory allocation and entrainment. The gas velocity in the standpipe is influenced by loop seal aeration and riser velocity. Variation in slugging behavior above and below solid downflow velocity of 0.025 m/s is analyzed and discussed here
Effect of precursor and surfactant nature on geometrical characteristics of mesoporous silicas
Bimodal mesoporous silicas and materials MCM-41 type were synthesized with the use as a template cationic surfactants distinguished by a length of the alkyl chain. Fumed silica, tetraethyl orthosilicate as well as of mixture these compounds were applied as a silicate precursor. Obtained samples have been characterized by the powder X-ray diffraction technique and adsorption measurements. Specific surface area, pore diameter, pore size distribution was determined from nitrogen ad(de)sorption isotherms at 77 K for the silicas prepared. The products with bimodal pore distribution have not ordered structure and contain macropores and mesopores, whose sizes are typical for MCM-41 materials. Effect of surfactant and precursor nature on the geometrical features of the ordered structure of MCM-41 type and bimodal porous materials was studied
Giant magnetocaloric effect in Mn 1-t (Ti 0.5 V 0.5 ) t as compounds near room temperature
International audienceMn 1-t (Ti 0.5 V 0.5) t As compounds with t varying from 0 to 0.20 were synthesised by arc melting and subsequently annealed. The X-ray diffraction analysis reveals pure and fairly crystallised samples. Magnetisation measurements show that the Curie temperature decreases to room temperature with t the substitution rate. The sharp and abrupt character of the 1 st order transition of MnAs-type turns to a less marked variation of the magnetic entropy in the vicinity of the transition temperature, profit made to a wider temperature range of MCE efficiency
High-pressure cryogelation of nanosilica and surface properties of cryosilicas
Silica cryogels (cryosilicas) in a powder state were synthesized with different concentrations of fumed silica A-300 (CA-300 = 5-20 wt.%), sonicated in aqueous suspension, then frozen at -14 oC at different pressures in a high-pressure stainless steel reactor (a freezing bomb), and dried in air at room temperature. To analyze the effects of low temperature and high pressure, samples were also prepared at -14 oC or room temperature and standard pressure. The structural and adsorption properties of the powder materials were studied using nitrogen adsorption, high-resolution transmission electron microscopy, infrared spectroscopy, thermogravimetry, low-temperature 1H NMR spectroscopy and thermally stimulated depolarization current. The structural, textural, adsorption and relaxation characteristics of high-pressure cryogel hydrogels and related dried powders are strongly dependent on the silica content in aqueous suspensions frozen at 1, 450 or 1000 atmospheres and then dried. The largest changes are found with CA-300 = 20 wt.% which are analyzed with respect to the interfacial behavior of nonpolar, weakly polar and polar adsorbates using low temperature 1H NMR spectroscopy
Autosomal recessive LRP1-related syndrome featuring cardiopulmonary dysfunction, bone dysmorphology, and corneal clouding.
We provide the first study of two siblings with a novel autosomal recessive LRP1-related syndrome identified by rapid genome sequencing and overlapping multiple genetic models. The patients presented with respiratory distress, congenital heart defects, hypotonia, dysmorphology, and unique findings, including corneal clouding and ascites. Both siblings had compound heterozygous damaging variants, c.11420G \u3e C (p.Cys3807Ser) and c.12407T \u3e G (p.Val4136Gly) i
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