1,085 research outputs found
Conceptual aspects of line tensions
We analyze two representative systems containing a three-phase-contact line:
a liquid lens at a fluid--fluid interface and a liquid drop in contact with a
gas phase residing on a solid substrate. We discuss to which extent the
decomposition of the grand canonical free energy of such systems into volume,
surface, and line contributions is unique in spite of the freedom one has in
positioning the Gibbs dividing interfaces. In the case of a lens it is found
that the line tension is independent of arbitrary choices of the Gibbs dividing
interfaces. In the case of a drop, however, one arrives at two different
possible definitions of the line tension. One of them corresponds seamlessly to
that applicable to the lens. The line tension defined this way turns out to be
independent of choices of the Gibbs dividing interfaces. In the case of the
second definition,however, the line tension does depend on the choice of the
Gibbs dividing interfaces. We provide equations for the equilibrium contact
angles which are form-invariant with respect to notional shifts of dividing
interfaces which only change the description of the system. Conceptual
consistency requires to introduce additional stiffness constants attributed to
the line. We show how these constants transform as a function of the relative
displacements of the dividing interfaces. The dependences of the contact angles
on lens or drop volumes do not render the line tension alone but a combination
of the line tension, the Tolman length, and the stiffness constants of the
line.Comment: 34 pages, 9 figure
Grand potential in thermodynamics of solid bodies and surfaces
Using the chemical potential of a solid in a dissolved state or the
corresponding component of the chemical potential tensor at equilibrium with
the solution, a new concept of grand thermodynamic potential for solids has
been suggested. This allows generalizing the definition of Gibbs' quantity
(surface work often called the solid-fluid interfacial free energy) at
a planar surface as an excess grand thermodynamic potential per unit surface
area that (1) does not depend on the dividing surface location and (2) is
common for fluids and solids.Comment: 6 page
Towards a gauge-polyvalent Numerical Relativity code
The gauge polyvalence of a new numerical code is tested, both in
harmonic-coordinate simulations (gauge-waves testbed) and in
singularity-avoiding coordinates (simple Black-Hole simulations, either with or
without shift). The code is built upon an adjusted first-order
flux-conservative version of the Z4 formalism and a recently proposed family of
robust finite-difference high-resolution algorithms. An outstanding result is
the long-term evolution (up to 1000M) of a Black-Hole in normal coordinates
(zero shift) without excision.Comment: to appear in Physical Review
Enhancement of the superconducting transition temperature in Nb/Permalloy bilayers by controlling the domain state of the ferromagnet
In (S/F) hybrids the suppression of superconductivity by the exchange field
h_ex of the ferromagnet can be partially lifted when different directions of
h_ex are sampled simultaneously by the Cooper pair. In F/S/F trilayer
geometries where the magnetization directions of the two F-layers can be
controlled separately, this leads to the so-called spin switch. Here we show
that domain walls in a single F-layer yield a similar effect. We study the
transport properties of Ni_0.8Fe_0.2/Nb bilayers structured in strips of
different sizes. For large samples a clear enhancement of superconductivity
takes place in the resistive transition, in the very narrow field range (order
of 0.5 mT) where the magnetization of the Py layer switches and many domains
are present. This effect is absent in microstructured samples. Comparison of
domain wall width \delta_w to the temperature dependent superconductor
coherence length \xi_S(T) shows that \delta_w ~ \xi_S(T), which means that the
Cooper pairs sample a large range of different magnetization directions.Comment: 4 pages, 5 figure
Bis[2-(hydroxyiminomethyl)phenolato]nickel(II): a second monoclinic polymorph
The title compound, [Ni(C7H6NO2)2], (I), is a second monoclinic polymorph of the compound, (II), reported by Srivastava et al. [Acta Cryst. (1967), 22, 922] and Mereiter [Private communication (2002) CCDC refcode NISALO01]. The bond lengths and angles are similar in both structures. The molecule in both structures lies on a crystallographic inversion center and both have an internal hydrogen bond. The title compound crystallizes in the space group P21/c (Z = 2), whereas compound (II) is in the space group P21/n (Z = 2) with a similar cell volume but different cell parameters. In both polymorphs, molecules are arranged in the layers but in contrast to the previously published compound (II) where the dihedral angle between the layers is 86.3°, in the title polymorph the same dihedral angle is 29.4°. The structure of (I) is stabilized by strong intramolecular O—H⋯O hydrogen bonding between the O—H group and the phenolate O atom
Distribution of periphytic diatoms in the rivers of the Lake Ladoga basin (Northwestern Russia).
Relationships between distribution of periphytic diatoms and environmental variables in 19 rivers of the Lake Ladoga basin (Northwestern Russia) were examined using gradient
analysis. On the basis of geology and river water chemistry, the Lake Ladoga basin could be separated into twomain parts, the northern and the southern sub-basin. The rivers in the northern sub-basin are slightly acidic and low in conductivity (mean value 53 mS cm–1); the rivers in the southern sub-basin have neutral to slightly alkaline waters with higher conductivities (mean value 168 mS cm–1). A detrended correspondence analysis (DCA)defined two groups of rivers generally corresponding to the two main parts of the Lake Ladoga basin. Fragilaria capucina var. rumpens, Frustulia saxonica and Tabellaria flocculosa were the typical species for the northern sub-basin, whereas Cocconeis placentula var. euglypta, Ulnaria ulna and Gomphonema parvulum were characteristic species
for the southern sub-basin. A canonical correspondence analysis (CCA) identified conductivity, pH, bicarbonate, total phosphorus and water colour as the most important
environmental variables related to changes in assemblage structure. Both DCA and CCA ordination showed that conductivity related to geology was the most important variable,while concentration of total phosphorus was the second most important variable.Weighted averaging was used to infer total phosphorus from relative biomass of diatoms. The predictive ability of the inference model was sufficiently strong with r2 = 0.71 and RMSEP =
1.9 mg L–1. These results strongly support the use of a diatom-based inference phosphorus model for indicating eutrophication in the rivers of the Lake Ladoga basin
Capillary pressure of van der Waals liquid nanodrops
The dependence of the surface tension on a nanodrop radius is important for
the new-phase formation process. It is demonstrated that the famous Tolman
formula is not unique and the size-dependence of the surface tension can
distinct for different systems. The analysis is based on a relationship between
the surface tension and disjoining pressure in nanodrops. It is shown that the
van der Waals interactions do not affect the new-phase formation thermodynamics
since the effect of the disjoining pressure and size-dependent component of the
surface tension cancel each other.Comment: The paper is dedicated to the 80th anniversary of A.I. Rusano
Development of the 500 kW and 1 MW ORC turbine flow parts
There paper presents two types of developed ORC turbines. The silica oil (MDM) is used as the working media. Proposed turbines are developed for electric power in 500 kW and 1 MW. For the designing of that turbines there were only one geometric constraint: the minimum height of the blade – 20 mm. The final 3D calculations of all turbine stages are provided with accounting the real properties of working media. Gasdynamic efficiency of the developed turbine flow parts is adequate for the such type of power machines.Рассмотрены несколько вариантов проточных частей осевых турбин мощностью 500 кВт и 1 МВт для когенерационной установки, использующей в качестве рабочего тела силиконовое масло (MDM). Единственным геометрическим ограничением для проектирования этих турбин было минимальная высота лопатки – 20 мм. Окончательные трехмерные расчеты всех ступеней турбины проведены с учетом реальных свойств рабочего тела на основе модифицированного уравнения состояния Бенедикта-Вебба-Рубина. Газодинамическая эффективность разработанных проточных частей турбин удовлетворяет требованиям, предъявляемым к энергетическим машинам подобного рода.Розглянуто декілька варіантів проточних частин осьових турбін потужністю 50 кВт та 1 МВт для когенераційної установки, що використовує як робоче тіло силіконове масло (MDM). Єдиним геометричним обмеженням для проектування цих турбін було мінімальна висота лопатки – 20 мм. Остаточні тривимірні розрахунки всіх ступенів турбіни проведено з урахуванням реальних властивостей робочого тіла на основі модифікованого рівняння стану Бенедикта-Вебба-Рубіна. Газодинамічна ефективність розроблених проточних частин турбін задовольняє вимоги, що ставляться до енергетичних машин подібного роду
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