490 research outputs found
Physicochemical investigation of anodic processes involved in silver electrowinning in refining technology
During silver electrowinning in refining technology, irrespectively of the nature of electrolyte and anode material, an anode deposit is formed due to oxidation of singly charged silver ions to higher degrees of oxidation (+2 and +3) under polarization. Absorption spectra of Ag(II) have been obtained in solutions with various concentrations of silver ions and nitric acid using anodic polarization in combination with electronic absorption spectroscopy; silver ions of high oxidation degrees were found to be unstable in solutions. At anode potentials φa ≥ 1.15-1.22 V, Ag(I) ions in liquid phase are oxidized to Ag(II), which paint the anolyte; their content depends on silver and nitric acid concentrations in the electrolyte. The deposit crystallizes on anode at potential φa ≈ 1.5 V. Chemical analysis, X-ray powder diffraction, and a thermogravimetric study of the anode deposit have made it possible to identify its initial composition as Ag 7O8NO3. The deposit composition varies in time as a result of reduction of highly oxidized silver. © 2013 Pleiades Publishing, Ltd
Transition from damage to fragmentation in collision of solids
We investigate fracture and fragmentation of solids due to impact at low
energies using a two-dimensional dynamical model of granular solids. Simulating
collisions of two solid discs we show that, depending on the initial energy,
the outcome of a collision process can be classified into two states: a damaged
and a fragmented state with a sharp transition in between. We give numerical
evidence that the transition point between the two states behaves as a critical
point, and we discuss the possible mechanism of the transition.Comment: Revtex, 12 figures included. accepted by Phys. Rev.
Fragmentation of a Circular Disc by Impact on a Frictionless Plate
The break-up of a two-dimensional circular disc by normal and oblique impact
on a hard frictionless plate is investigated by molecular dynamics simulations.
The disc is composed of numerous unbreakable randomly shaped convex polygons
connected together by simple elastic beams that break when bent or stretched
beyond a certain limit. It is found that for both normal and oblique impacts
the crack patterns are the same and depend solely on the normal component of
the impact velocity. Analysing the pattern of breakage, amount of damage,
fragment masses and velocities, we show the existence of a critical velocity
which separates two regimes of the impact process: below the critical point
only a damage cone is formed at the impact site (damage), cleaving of the
particle occurs at the critical point, while above the critical velocity the
disc breaks into several pieces (fragmentation). In the limit of very high
impact velocities the disc suffers complete disintegration (shattering) into
many small fragments. In agreement with experimental results, fragment masses
are found to follow the Gates-Gaudin-Schuhmann distribution (power law) with an
exponent independent of the velocity and angle of impact. The velocity
distribution of fragments exhibit an interesting anomalous scaling behavior
when changing the impact velocity and the size of the disc.Comment: submitted to J. Phys: Condensed Matter special issue on Granular
Medi
National interests of the USA and Russia: comparative legal analysis
This article is devoted to the comparative analysis of doctrinal approaches concerning the determination of national interests in the USA and Russia, their legal consolidation and implementation practice in modern conditions. The features of the North American and Russian approaches to the issues of strategic planning and the development of program documents in the field of national interest provision are established and systematize
Skew-self-adjoint discrete and continuous Dirac type systems: inverse problems and Borg-Marchenko theorems
New formulas on the inverse problem for the continuous skew-self-adjoint
Dirac type system are obtained. For the discrete skew-self-adjoint Dirac type
system the solution of a general type inverse spectral problem is also derived
in terms of the Weyl functions. The description of the Weyl functions on the
interval is given. Borg-Marchenko type uniqueness theorems are derived for both
discrete and continuous non-self-adjoint systems too
Ring switching tricomponent synthesis of pyrano[2,3-b]pyridine multifunctional derivatives
New 3-acylamino-7-hydroxy-5-methyl-2-oxo-2H-pyrano[2,3-b]pyridine-6-carbonitriles were synthesized via a tricomponent condensation of 3-cyano-4-methyl-1,2,5,6-tetrahydropyridine- 2,6-dione, triethyl orthoformate and N-acylglycines under the Erlenmeyer-Plöchl reaction conditions. According to X-ray data, in the solid phase they exist as hydroxypyridine tautomer for
Force Distribution in a Granular Medium
We report on systematic measurements of the distribution of normal forces
exerted by granular material under uniaxial compression onto the interior
surfaces of a confining vessel. Our experiments on three-dimensional, random
packings of monodisperse glass beads show that this distribution is nearly
uniform for forces below the mean force and decays exponentially for forces
greater than the mean. The shape of the distribution and the value of the
exponential decay constant are unaffected by changes in the system preparation
history or in the boundary conditions. An empirical functional form for the
distribution is proposed that provides an excellent fit over the whole force
range measured and is also consistent with recent computer simulation data.Comment: 6 pages. For more information, see http://mrsec.uchicago.edu/granula
Infinite-dimensional -adic groups, semigroups of double cosets, and inner functions on Bruhat--Tits builldings
We construct -adic analogs of operator colligations and their
characteristic functions. Consider a -adic group , its subgroup , and the subgroup
embedded to diagonally. We show that double cosets
admit a structure of a semigroup, acts naturally in -fixed vectors
of unitary representations of . For each double coset we assign a
'characteristic function', which sends a certain Bruhat--Tits building to
another building (buildings are finite-dimensional); image of the distinguished
boundary is contained in the distinguished boundary. The latter building admits
a structure of (Nazarov) semigroup, the product in corresponds to a
point-wise product of characteristic functions.Comment: new version of the paper, 47pp, 3 figure
In Memoriam, Academician Prof. Dr. Osor Shagdarsuren (1929-2010)
Academician, Professor Osor Shagdarsuren passed away due to apoplexy on Tuesday, February 2, 2010, at the age of 81. He was one of the most respected Mongolian ornithologists, biologists, and educators. The Mongolian scientific community has lost one of its greatest members, the premier Mongolian ornithologist
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