We have used the time differential perturbed angular correlation (TDPAC) spectroscopy to measure the electric and magnetic hyperfine fields in RhGe crystallized in the B20 cubic lattice structure and ...weakly doped with Hf (0.5–2 atomic %) in the temperature range from 5 K to 295 K. Two most commonly used nuclei probes, 111In→111Cd and 181Hf→181Ta, have been used. The experimental results combined with theoretical density functional calculations indicate that the In/Cd impurities substitute into the Ge-site whereas the Ta/Hf probes substitute into the Rh-site. It has also been found that the Ta/Hf impurity strongly distorts the local crystal environment, whereas the effect from the In/Cd probe is weak. There are no reliable evidences of the magnetic order in the studied alloys at low temperatures.
•Novel high-pressure phases.•Local studies of both lattice sites in RhGe.•Study of the very weak magnetism in noncentrosymmetric superconductor.•TDPAC measurements on two most commonly used nuclei probes.•TDPAC measurements at low temperatures.•Digital TDPAC spectrometer.
The positron annihilation lifetimes were measured using a 48V positron source in noncentrosymmetric cubic single crystals of CoSi, FeSi and MnSi. The following lifetimes were determined from the ...positron annihilation time spectra: 168(1) ps for CoSi, 114(1) ps for FeSi and 111(1) ps for MnSi. For single-crystal CoSi, the positron annihilation lifetime was also determined with a 22Na positron source. For CoSi, the lifetimes obtained from different positron sources are consistent. The differences in the positron annihilation lifetimes in MnSi and FeSi, on the one hand, and in the Weyl semimetal CoSi, on the other hand, are possibly caused by the formation of a positron + electron bound state (positronium).
Numerical algorithm is developed for modelling non-linear mass transfer process in supercritical fluid extraction (SFE). The ground raw material is considered as polydisperse, characterized by ...discrete number of effective particle fractions. Two continuous interacting counterparts separated by permeable membrane are distinguished in plant material build-up. The apoplast plays role of transport channels during extraction, and symplast contains extractable oil. The complete SFE model is non-linear as a result of non-linearity of oil dissolution kinetics. The computational scheme is based on the finite-volume approximation method and Thomas elimination procedure. The resulting system of algebraic equations is solved iteratively. Special attention is paid to polydisperse substrates, when particle scale characteristics of all fractions interact with each other through pore phase concentration on the vessel scale. Stability of the developed algorithm is demonstrated in numerical tests. Special iterative procedure guarantees a monotonic decrease of oil content in individual particles of substrate. It is also shown that in the limit of the so-called shrinking core approach the number of mesh nodes on a particle scale should be increased.
Hyperfine interactions in the Bi
1−
x
La
x
FeO
3
ferrites (where
x
= 0.0225, 0.075, 0.9) have been studied by means of
57
Fe Mössbauer spectroscopy and
140
Ce time differential perturbed angular
γ
–
...γ
correlation methods. The information about the line shift
δ
, the lattice
ε
lat
and the magnetic
ε
mag
contributions to the quadrupole shift
ε
, isotropic
H
is
and anisotropic
H
an
contributions to the hyperfine magnetic field
H
hf
on
57
Fe nuclei, anharmonicity parameter
m
, distribution of the hyperfine magnetic field
p
(
H
hf
), and supertransferred hyperfine magnetic fields on
140
Ce probe nuclei were obtained. In all studied compounds, the Fe ions are in a high-spin trivalent state. In the compounds with
x
= 0.0225 and 0.075 spatially modulated cycloidal magnetic structures exist. It was found that the sign of the effective constant of magnetic anisotropy
K
eff
changes with the variation of
x
from 0.0225 to 0.075. The substitution of Bi by La increases the value of the hyperfine magnetic field on
57
Fe nuclei from 494 kOe in Bi
0.9775
La
0.0225
FeO
3
to 520 kOe in Bi
0.1
La
0.9
FeO
3
, i.e. by 26 kOe, while the corresponding supertransferred hyperfine magnetic field on
140
Ce probe nuclei decreases.
The boundary value problem of transient pressure field development around a horizontal well in a laterally infinite, inhomogeneous, anisotropic reservoir is formulated under assumption of slow ...spatial variation of the matrix permeability along the well axis. The well is represented as a linear fluid source/sink. The pressure distribution is expressed in the integral form on the basis of the instant point source perturbation function found explicitly. The inverse problem for fluid in/outflow density rates simulation is reduced to solution of the integral equation at a given pressure inside the well. A computational procedure is developed and implemented to predict the in/outflow rates along the well and estimate the impact of the permeability variations on the well performance. Series of calculations for constant, linear, and variable permeability cases are analyzed and compared. The difference of the obtained solution from the so-called “locally-constant” permeability approximation is demonstrated, accuracy and applicability of the latter approach are discussed.
Fluid-feeding insects have evolved a unique strategy to distribute the labor between a liquid-acquisition device (proboscis) and a sucking pump. We theoretically examined physical constraints ...associated with coupling of the proboscis and sucking pump into a united functional organ. Classification of fluid feeders with respect to the mechanism of energy dissipation is given by using only two dimensionless parameters that depend on the length and diameter of the proboscis food canal, maximum expansion of the sucking pump chamber, and chamber size. Five species of Lepidoptera - White-headed prominent moth (Symmerista albifrons), White-dotted prominent moth (Nadata gibosa), Monarch butterfly (Danaus plexippus), Carolina sphinx moth (Manduca sexta), and Death's head sphinx moth (Acherontia atropos) - were used to illustrate this classification. The results provide a rationale for categorizing fluid-feeding insects into two groups, depending on whether muscular energy is spent on moving fluid through the proboscis or through the pump. These findings are relevant to understanding energetic costs of evolutionary elaboration and reduction of the mouthparts and insect diversification through development of new habits by fluid-feeding insects in general and by Lepidoptera in particular.
The general hydrodynamic equations of a mathematical model for supercritical fluid extraction are derived within the framework of the continuum mechanics approach. The shrinking core concept is used ...to describe the mass transfer on the solid-liquid interface. The complete system of macroscopic differential mass-balance equations is reduced to a one-dimensional approximation and accounts for the axial dispersion effect. Correlation formulas available in the literature are used to calculate the axial dispersion coefficient for the conditions of supercritical CO
2
filtration. The effect of axial dispersion on the characteristics of the macroscopic process is analyzed for the typical laboratory-scale extraction conditions in the framework of the suggested model. The numerical simulations demonstrate that the difference between the values of the current mass of accumulated extract calculated in terms of the complete approach, which accounts for the axial dispersion, and the one related to the simplified model (in which the axial dispersion is neglected), is less than 10%. The same comparison is made for the outlet concentrations of the target compounds; the difference reaches 200%.
The problem of evaluation of model parameters for supercritical fluid extraction of oil from ground plant materials with high initial oil contents was studied. The information content of laboratory ...experimental data was analyzed by the Markov chain Monte Carlo method. The accuracy of evaluation of the main effective parameters of the model was determined for the apparent diffusion coefficient, saturation concentration of oil in the solvent, and the total content of target compounds in the raw material. Various parameterizations of the inverse problem were considered. Given the initial oil content, the diffusion coefficient can be evaluated from the individual overall extraction curve corresponding to coarse grinding. At the same time, simultaneous evaluation of all the three parameters is possible only with combined analysis of at least two curves corresponding to fine and coarse grinding. The experiment with fine grinding allows identification of only the total content of the target compounds and the saturation concentration, but cannot be used to evaluate the apparent diffusion coefficient.
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