99 research outputs found
Lattice Models of Ionic Systems
A theoretical analysis of Coulomb systems on lattices in general dimensions
is presented. The thermodynamics is developed using Debye-Huckel theory with
ion-pairing and dipole-ion solvation, specific calculations being performed for
3D lattices. As for continuum electrolytes, low-density results for sc, bcc and
fcc lattices indicate the existence of gas-liquid phase separation. The
predicted critical densities have values comparable to those of continuum ionic
systems, while the critical temperatures are 60-70% higher. However, when the
possibility of sublattice ordering as well as Debye screening is taken into
account systematically, order-disorder transitions and a tricritical point are
found on sc and bcc lattices, and gas-liquid coexistence is suppressed. Our
results agree with recent Monte Carlo simulations of lattice electrolytes.Comment: 25 pages, 3 figures, ReVTeX 4, Submitted to J. Chem. Phy
Lattice Models of Ionic Systems with Charge Asymmetry
The thermodynamics of a charge-asymmetric lattice gas of positive ions
carrying charge and negative ions with charge is investigated using
Debye-H\"uckel theory. Explicit analytic and numerical calculations, which take
into account the formation of neutral and charged clusters and cluster
solvation by the residual ions, are performed for , 3 and 4. As charge
asymmetry increases, the predicted critical point shifts to lower temperatures
and higher densities. This trend agrees well with the results from recent Monte
Carlo simulations for continuum charge-asymmetric hard-sphere ionic fluids and
with the corresponding predictions from continuum Debye-H\"uckel theory.Comment: submitted to J.Chem.Phy
Fermi-liquid theory of the surface impedance of a metal in a normal magnetic field
In this paper we present detailed theoretical analysis of the frequency
and/or magnetic field dependence of the surface impedance of a metal at the
anomalous skin effect. We calculate the surface impedance in the presence of a
magnetic field directed along the normal to the metal surface. The effects of
the Fermi-liquid interactions on the surface impedance are studied. It is shown
that the cyclotron resonance in a normal magnetic field may be revealed {\it
only and exclusively} in such metals whose Fermi surfaces include segments
where its Gaussian curvature turns zero. The results could be applied to
extract extra informations concerning local anomalies in the Fermi surface
curvature in conventional and quasi-two-dimensional metals.Comment: 10 pages, 1 figure, text added and rearranged, computational details
are moved into Appendice
Effect of the entropy on the shear viscosity of metallic glasses near the glass transition
We measured the shear viscosity of 14 metallic glasses differing with their
mixing entropy . It is found that the viscosity at the glass
transition temperature significantly increases with .
Using calorimetric data, we calculated the excess entropy of all glasses
with respect to their maternal crystalline states as a function of
temperature. It is shown that the excess entropy both at room
temperature and at \textit{decreases} with . It is
concluded that glasses with "high mixing entropy" correspond
to MGs with \textit{low} excess entropy . The origin of the increased
shear viscosity at of glasses with high is determined by
their reduced excess entropy .Comment: 12 pages, 4 Figure
Relation of the thermodynamic parameter of disordering with the width of structure factor and defect concentration in a metallic glass
In this work, we show that above the glass transition there exists a strong
unique interrelationship between the thermodynamic parameter of disorder of a
metallic glass derived using its excess entropy, diffraction measure of
disorder given by the width of the X-ray structure factor and defect
concentration derived from shear modulus measurements. Below the glass
transition, this relationship is more complicated and depends on both
temperature and thermal prehistory.Comment: 6 pages, 2 Figure
Thermodynamics of Electrolytes on Anisotropic Lattices
The phase behavior of ionic fluids on simple cubic and tetragonal
(anisotropic) lattices has been studied by grand canonical Monte Carlo
simulations. Systems with both the true lattice Coulombic potential and
continuous-space electrostatic interactions have been investigated. At
all degrees of anisotropy, only coexistence between a disordered low-density
phase and an ordered high-density phase with the structure similar to ionic
crystal was found, in contrast to recent theoretical predictions. Tricritical
parameters were determined to be monotonously increasing functions of
anisotropy parameters which is consistent with theoretical calculations based
on the Debye-H\"uckel approach. At large anisotropies a two-dimensional-like
behavior is observed, from which we estimated the dimensionless tricritical
temperature and density for the two-dimensional square lattice electrolyte to
be and .Comment: submitted to PR
Critical behavior of the fluctuation heat capacity near the glass transition of metallic glasses
The high-frequency shear modulus of five Zr-, Pd-, Cu-based conventional and
two high-entropy bulk metallic glasses was measured in a wide temperature range
up to the beginning of crystallization. Using these data and general
thermodynamic relations, the "fluctuation" heat capacity
determined by local structural fluctuations in the defect regions is introduced
and calculated. It is found that temperature dependence for all
metallic glasses has a large peak located slightly below or above the glass
transition temperature but clearly lower than the crystallization onset
temperature. The form of this peak resembles the characteristic -peak
typical for order-disorder phase transitions. It is suggested that this -peak reflects certain underlying critical phenomenon. The critical
temperature (peak temperature) and corresponding critical index
are determined. Averaged over all seven metallic glasses under investigation in
the initial and relaxed states, the critical index . The results
obtained indicate that the fluctuations of thermal energy near the glass
transition bear the marks of a continuous phase transition. However, the
derived critical index is between those corresponding to a second-order phase
transition () and a critical transition characterized by a
tricritical point ().Comment: 18 pages, 4 figure
Origin of elemental carbon in snow from western Siberia and northwestern European Russia during winter-spring 2014, 2015 and 2016
Short-lived climate forcers have been proven important both for the climate and human health. In particular, black carbon (BC) is an important climate forcer both as an aerosol and when deposited on snow and ice surface because of its strong light absorption. This paper presents measurements of elemental carbon (EC; a measurement-based definition of BC) in snow collected from western Siberia and northwestern European Russia during 2014, 2015 and 2016. The Russian Arctic is of great interest to the scientific community due to the large uncertainty of emission sources there. We have determined the major contributing sources of BC in snow in western Siberia and northwestern European Russia using a Lagrangian atmospheric transport model. For the first time, we use a recently developed feature that calculates deposition in backward (so-called retroplume) simulations allowing estimation of the specific locations of sources that contribute to the deposited mass
Intermolecular Photocatalytic Chemo‐, Stereo‐ and Regioselective Thiol–Yne–Ene Coupling Reaction
The first example of an intermolecular thiol–yne–ene coupling reaction is reported for the one-pot construction of C−S and C−C bonds. Thiol–yne–ene coupling opens a new dimension in building molecular complexity to access densely functionalized products. The employment of Eosin Y/DBU/MeOH photocatalytic system suppresses hydrogen atom transfer (HAT) and associative reductant upconversion (via C−S three-electron σ-bond formation). Investigation of the reaction mechanism by combining online ESI-UHRMS, EPR spectroscopy, isotope labeling, determination of quantum yield, cyclic voltammetry, Stern–Volmer measurements and computational modeling revealed a unique photoredox cycle with four radical-involving stages. As a result, previously unavailable products of the thiol–yne–ene reaction were obtained in good yields with high selectivity. They can serve as stable precursors for synthesizing synthetically demanding activated 1,3-dienes
Origin of elemental carbon in snow from western Siberia and northwestern European Russia during winter–spring 2014, 2015 and 2016
Short-lived climate forcers have been proven important both for the climate
and human health. In particular, black carbon (BC) is an important climate
forcer both as an aerosol and when deposited on snow and ice surface because
of its strong light absorption. This paper presents measurements of elemental
carbon (EC; a measurement-based definition of BC) in snow collected from
western Siberia and northwestern European Russia during 2014, 2015 and 2016.
The Russian Arctic is of great interest to the scientific community due to
the large uncertainty of emission sources there. We have determined the major
contributing sources of BC in snow in western Siberia and northwestern
European Russia using a Lagrangian atmospheric transport model. For the first
time, we use a recently developed feature that calculates deposition in
backward (so-called retroplume) simulations allowing estimation of the
specific locations of sources that contribute to the deposited mass.
EC concentrations in snow from western Siberia and northwestern European
Russia were highly variable depending on the sampling location. Modelled BC
and measured EC were moderately correlated (R = 0.53–0.83) and a systematic
region-specific model underestimation was found. The model underestimated
observations by 42 % (RMSE = 49 ng g−1) in 2014, 48 % (RMSE = 37 ng g−1)
in 2015 and 27 % (RMSE = 43 ng g−1) in 2016. For EC
sampled in northwestern European Russia the underestimation by the model was
smaller (fractional bias, FB > −100 %). In this region, the
major sources were transportation activities and domestic combustion in
Finland. When sampling shifted to western Siberia, the model underestimation
was more significant (FB < −100 %). There, the sources included
emissions from gas flaring as a major contributor to snow BC. The accuracy
of the model calculations was also evaluated using two independent datasets
of BC measurements in snow covering the entire Arctic. The model
underestimated BC concentrations in snow especially for samples collected in
springtime
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