114 research outputs found
Field-theoretic description of ionic crystallization in the restricted primitive model
Effects of charge-density fluctuations on a phase behavior of the restricted
primitive model (RPM) are studied within a field-theoretic formalism. We focus
on a -line of continuous transitions between charge-ordered and
charge-disordered phases that is observed in several mean-field (MF) theories,
but is absent in simulation results. In our study the RPM is reduced to a
theory, and a fluctuation contribution to a grand thermodynamic
potential is obtained by generalizing the Brazovskii approach. We find that in
a presence of fluctuations the -line disappears. Instead, a
fluctuation-induced first-order transition to a charge-ordered phase appears in
the same region of a phase diagram, where the liquid -- ionic-crystal
transition is obtained in simulations. Our results indicate that the
charge-ordered phase should be identified with an ionic crystal.Comment: 31 pages, 10 figure
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
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
Observation of Magnetic Monopoles in Spin Ice
Excitations from a strongly frustrated system, the kagome ice state of the
spin ice Dy2Ti2O7 under magnetic fields along a [111] direction, have been
studied. They are theoretically proposed to be regarded as magnetic monopoles.
Neutron scattering measurements of spin correlations show that close to the
critical point the monopoles are fluctuating between high- and low-density
states, supporting that the magnetic Coulomb force acts between them. Specific
heat measurements show that monopole-pair creation obeys an Arrhenius law,
indicating that the density of monopoles can be controlled by temperature and
magnetic field.Comment: 5 pages, 4 figures; International Conference on Neutron Scattering
2009 (May 7); J. Phys. Soc. Jpn. 78, No.10 (2009) (Received Aug 11, 2009;
accepted Sept 8, 2009; published Oct 13, 2009
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
Quantitative imaging of concentrated suspensions under flow
We review recent advances in imaging the flow of concentrated suspensions,
focussing on the use of confocal microscopy to obtain time-resolved information
on the single-particle level in these systems. After motivating the need for
quantitative (confocal) imaging in suspension rheology, we briefly describe the
particles, sample environments, microscopy tools and analysis algorithms needed
to perform this kind of experiments. The second part of the review focusses on
microscopic aspects of the flow of concentrated model hard-sphere-like
suspensions, and the relation to non-linear rheological phenomena such as
yielding, shear localization, wall slip and shear-induced ordering. Both
Brownian and non-Brownian systems will be described. We show how quantitative
imaging can improve our understanding of the connection between microscopic
dynamics and bulk flow.Comment: Review on imaging hard-sphere suspensions, incl summary of
methodology. Submitted for special volume 'High Solid Dispersions' ed. M.
Cloitre, Vol. xx of 'Advances and Polymer Science' (Springer, Berlin, 2009);
22 pages, 16 fig
КОРА И МАНТИЯ БАЙКАЛЬСКОЙ РИФТОВОЙ ЗОНЫ ПО ДАННЫМ ПРИЕМНЫХ ФУНКЦИЙ ПРОДОЛЬНЫХ И ПОПЕРЕЧНЫХ ВОЛН
We have obtained P-wave and S-wave receiver functions for 10 broadband seismograph stations in the Baikal rift zone (BRZ) and inverted them for seismic velocity models of the crust and upper mantle. The thinnest crust (30–35 km) is found in the Baikal basin, the thickest in the East Sayan uplift (45–50 km). Intermediate values (40 km) are found in the BRZ at distances around 100 km from Lake Baikal. A high (at least 1.8) Vp/Vs ratio is observed in the middle and lower crust. It exceeds 2.0 at some stations. In our opinion, the highest Vp/Vs ratios are due to fluid-filled porosity with a high pore pressure. The seismic lithosphere – asthenosphere boundary (LAB) is manifested by a shear velocity drop from 4.5 km/s to 4.0–4.2 km/s. Beneath the Baikal basin, the LAB is located at a depth not more than 50 km, and the S velocity drop is maximal (10 %). A similar structure is found outside the basin, underneath a segment of the East Sayan uplift. At other locations in the BRZ, a typical depth of the LAB varies from 80 to 90 km. Having considered changes in the depth of the 410 km seismic discontinuity, we cannot find any evidence of an elevated temperature of a hypothetical thermal plume beneath the BRZ. Для десяти широкополосных сейсмических станций в Байкальской рифтовой зоне получены приемные функции продольных и поперечных волн и выполнено их совместное обращение в скоростные разрезы. Самая тонкая кора (30–35 км) приурочена к Байкальской впадине, самая толстая – к Восточному Саяну (45–50 км). Промежуточные значения (около 40 км) получены в БРЗ на удалениях около 100 км от Байкала. В средней и нижней коре систематически наблюдается высокое (не менее 1.8) отношение скоростей Vp/Vs, которое на нескольких станциях превышает 2.0. Самые высокие значения мы объясняем присутствием флюида с высоким поровым давлением. Сейсмическая граница литосфера – астеносфера проявляется падением скорости поперечных волн с глубиной от 4.5 до 4.0–4.2 км/с. Под Байкальской впадиной эта граница находится на глубинах, не превышающих 50 км, и понижение скорости поперечных волн в астеносфере достигает максимальных значений (около 10 %). За пределами Байкальской впадины сходная структура наблюдается под частью Восточного Саяна. В остальных случаях характерное значение глубины границы литосфера – астеносфера составляет 80–90 км. Повышение температуры в гипотетическом мантийном плюме под БРЗ по изменению глубины 410-километровой сейсмической границы не обнаружено
Time-aging time-stress superposition in soft glass under tensile deformation field
We have studied the tensile deformation behaviour of thin films of aging
aqueous suspension of Laponite, a model soft glassy material, when subjected to
a creep flow field generated by a constant engineering normal stress. Aqueous
suspension of Laponite demonstrates aging behaviour wherein it undergoes time
dependent enhancement of its elastic modulus as well as its characteristic
relaxation time. However, under application of the normal stress, the rate of
aging decreases and in the limit of high stress, the aging stops with the
suspension now undergoing a plastic deformation. Overall, it is observed that
the aging that occurs over short creep times at small normal stresses is same
as the aging that occurs over long creep times at large normal stresses. This
observation allows us to suggest an aging time - process time - normal stress
superposition principle, which can predict rheological behaviour at longer
times by carrying out short time tests.Comment: 26 pages, 7 figures, To appear in Rheologica Act
On the polyamorphism of fullerite-based orientational glasses
The dilatometric investigation in the temperature range of 2-28K shows that a
first-order polyamorphous transition occurs in the orientational glasses based
on C60 doped with H2, D2 and Xe. A polyamorphous transition was also detected
in C60 doped with Kr and He. It is observed that the hysteresis of thermal
expansion caused by the polyamorphous transition (and, hence, the transition
temperature) is essentially dependent on the type of doping gas. Both positive
and negative contributions to the thermal expansion were observed in the low
temperature phase of the glasses. The relaxation time of the negative
contribution occurs to be much longer than that of the positive contribution.
The positive contribution is found to be due to phonon and libron modes, whilst
the negative contribution is attributed to tunneling states of the C60
molecules. The characteristic time of the phase transformation from the low-T
phase to the high-T phase has been found for the C60-H2 system at 12K. A
theoretical model is proposed to interpret these observed phenomena. The
theoretical model proposed, includes a consideration of the nature of
polyamorphism in glasses, as well as the thermodynamics and kinetics of the
transition. A model of non-interacting tunneling states is used to explain the
negative contribution to the thermal expansion. The experimental data obtained
is considered within the framework of the theoretical model. From the
theoretical model the order of magnitude of the polyamorphous transition
temperature has been estimated. It is found that the late stage of the
polyamorphous transformation is described well by the Kolmogorov law with an
exponent of n=1. At this stage of the transformation, the two-dimensional phase
boundary moves along the normal, and the nucleation is not important.Comment: 29 pages, 14 figures, added references, corrected typo
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