81 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
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
A thermodynamic unification of jamming
Fragile materials ranging from sand to fire-retardant to toothpaste are able
to exhibit both solid and fluid-like properties across the jamming transition.
Unlike ordinary fusion, systems of grains, foams and colloids jam and cease to
flow under conditions that still remain unknown. Here we quantify jamming via a
thermodynamic approach by accounting for the structural ageing and the
shear-induced compressibility of dry sand. Specifically, the jamming threshold
is defined using a non-thermal temperature that measures the 'fluffiness' of a
granular mixture. The thermodynamic model, casted in terms of pressure,
temperature and free-volume, also successfully predicts the entropic data of
five molecular glasses. Notably, the predicted configurational entropy avoids
the Kauzmann paradox entirely. Without any free parameters, the proposed
equation-of-state also governs the mechanism of shear-banding and the
associated features of shear-softening and thickness-invariance.Comment: 16 pgs double spaced. 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.
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
ГЛУБИННОЕ СТРОЕНИЕ ПЕРЕХОДНОЙ ЗОНЫ СИБИРСКАЯ ПЛАТФОРМА – ЦЕНТРАЛЬНО-АЗИАТСКИЙ ПОДВИЖНЫЙ ПОЯС ПО ТЕЛЕСЕЙСМИЧЕСКИМ ДАННЫМ
Deep velocity sections of the transition zone from the Siberian platform to the Central Asian mobile belt are constructed by teleseismic tomography and P-receiver function techniques. An array of the dense ancient Siberian craton is identified in the velocity sections with areas of high seismic velocity. In the SSW section MOBAL_2003, the surface boundary of the craton corresponds to the southern margin of the Siberian platform and is nearly vertical to a depth of 120 km. At larger depths, the craton slides almost horizontally underneath the Tunka rift area. At depths from 150 to 250 km, it is in contact with the area under the Khamar-Daban mountain range. In the southeast, according to the SE velocity section PASSCAL_1992 across the South Baikal basin and the Khamar-Daban mountain range, the Siberian craton thickness is reduced from 270 to 150 km at the contact of the Siberian platform with the Baikal folded area. In this contact zone, the upper part of the craton is wedge-shaped and has an angle of about 45° with the ground surface; it completely tapers off at a depth of 150 km to the east of Lake Baikal. The vertical configuration of the southern segment of the Siberian craton, which evolved with time, may determine the nature of the Baikal rifting in the Cenozoic. По скоростным разрезам, построенным методами телесейсмической томографии и продольной приемной функции, найдены особенности вертикальной конфигурации юга Сибирского кратона, влияющие на Байкальский рифтогенез. Кратон ассоциируется с выявленными на моделях областями повышенной сейсмической скорости. На юго-юго-западном разрезе MOBAL_2003 граница кратона на поверхности соответствует южной окраине Сибирской платформы и до глубины 120 км близка к вертикали. Глубже кратон почти горизонтально уходит под Тункинский рифт, достигая подножия Хамар-Дабана в интервале глубин 150–250 км. На юго-востоке вертикальная конфигурация границы кратона выявляется по форме высокоскоростной аномалии разреза PASSCAL_1992, пересекающего Южнобайкальскую впадину и Хамар-Дабан. Мощность аномалии, свидетельствующей о более высокоскоростной и плотной среде, на контакте Сибирской платформы с Байкальской складчатой областью уменьшается от 270 до 150 км. В районе контакта высокоскоростная аномалия принимает форму клина, который под углом около 45° задвигается от дневной поверхности под озеро Байкал и на глубине 150 км выклинивается восточнее озера.
Реакция ледников Полярного Урала на современные изменения климата
Monitoring of glacier mass balance is usually focused on analysis of middle and large glaciers, so small glaciers on the verge of extinction remain out of the attention of researchers. Studies of glaciers of the Polar Urals, begun in the mid-twentieth century, present in this respect interesting information. The series of observations of them is the longest among other glaciers of the mountainous regions of the Russian mainland in the polar latitudes. New results of quantitative assessment of changes in the size and mass balance of glaciers in this region are presented. To estimate the geodetic balance of the IGAN Glacier, data from photogeodetic surveys of 1963, data of ground-based DGPS surveys of 2008 and 2018 together with a fragment of the digital elevation model (DEM) of the ArcticDEM v3.0 of 2016 were used. Using these data, the DEM of its surface was calculated as of 1963, 2008, and 2018, and the changes in the glacier volume were estimated for the period from 1963 to 2018, during which the glacier had lost 19.7 million m3 of ice, of which 3.2 million m3 were lost in the last decade. The average decrease in the surface height was 18.94±3.22 m, and the maximum – 53.5±1.0 m. In 1963–2008, the specific massbalance was equal to −317±59 mm w.e./year, while in 2008–2018 −336±61 mm/year. Estimation of changes in the size of 30 glaciers of the Polar Urals made from images of the Sentinel-2 satellite had shown that in 2000– 2018 the glaciers lost 2.02 km2 (about 28%) of the area. In comparison with the period of 1953–2000, the average annual rate of reduction of their area doubled and amounted to 0.112 km2/year (1.54%/year). Magnitudes of the reduction of individual glaciers are not identical. Within the selection of 30 glaciers, they vary from 7.1% (the Terentyev Glacier) to 61.1% (the Oleniy Glacier). The analysis of changes in temperature and precipitation in 2000–2018 allows us making the conclusion that the reason for the accelerated reduction of glaciers in the Polar Urals in these years is the rise of summer air temperature since beginning of the twentieth century by 1.5 °C, to which the lowering of winter precipitation was added in the last decade.По данным фотогеодезических съёмок 1963 г., наземных DGPS‐съёмок 2008 и 2018 гг. и космических снимков оценены изменения геодезического баланса ледника ИГАН и размеров 30 ледников Полярного Урала с 1953 по 2018 г. По сравнению с 1953 г. площадь ледников продолжает сокращаться с возрастающей скоростью; с начала ХХI в. она увеличилась в 2 раза. С 1953 г. ледник ИГАН потерял 19,7 млн м3 льда, его высота в среднем понизилась на 19 м
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
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
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