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Philos Trans A Math Phys Eng Sci 2020 May 13;378(2171):20190540. Epub 2020 Apr 13.

Interdisciplinary Centre for Advanced Materials Simulation, Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum, Germany.

The thin interface limit of the phase-field model is extended to include transport via melt convection. A double-sided model (equal diffusivity in liquid and solid phases) is considered for the present analysis. For the coupling between phase-field and Navier-Stokes equations, two commonly used schemes are investigated using a matched asymptotic analysis: (i) variable viscosity and (ii) drag force model. Read More

Philos Trans A Math Phys Eng Sci 2020 May 13;378(2171):20190243. Epub 2020 Apr 13.

Department of Theoretical and Mathematical Physics, Laboratory of Multi-Scale Mathematical Modeling, Ural Federal University, Ekaterinburg 620000, Russian Federation.

The present article is focused on the shapes of dendritic tips occurring in undercooled binary systems in the absence of convection. A circular/globular shape appears in limiting cases of small and large Péclet numbers. A parabolic/paraboloidal shape describes the tip regions of dendrites whereas a fractional power law defines a shape behind their tips in the case of low/moderate Péclet number. Read More

Philos Trans A Math Phys Eng Sci 2020 May 13;378(2171):20190248. Epub 2020 Apr 13.

Department of Theoretical and Mathematical Physics, Laboratory of Multi-Scale Mathematical Modeling, Ural Federal University, Ekaterinburg, 620000, Russian Federation.

A nonlinear problem with two moving boundaries of the phase transition, which describes the process of directional crystallization in the presence of a quasi-equilibrium two-phase layer, is solved analytically for the steady-state process. The exact analytical solution in a two-phase layer is found in a parametric form (the solid phase fraction plays the role of this parameter) with allowance for possible changes in the density of the liquid phase accordingly to a linearized equation of state and arbitrary value of the solid fraction at the boundary between the two-phase and solid layers. Namely, the solute concentration, temperature, solid fraction in the mushy layer, liquid and solid phases, mushy layer thickness and its velocity are found analytically. Read More

Phys Rev E 2019 Nov;100(5-1):053203

Institut für Optik und Quantenelektronik, Physikalisch-Astronomische Fakultät, Friedrich-Schiller-Universität, Max-Wien Platz 1, D-07743 Jena, Germany.

Single-cycle pulses with multimillion volts per centimeter field strengths and spectra in the terahertz (THz) band have attracted great interest due to their ability to coherently manipulate molecular orientations and electron spins resonantly and nonresonantly. The tremendous progress made in the development of compact and powerful terahertz sources have identified intense laser-thin foil interaction as a potential candidate for high-power broadband terahertz radiation. They are micrometers in size and deliver radially polarized terahertz pulses with millijoule energy and gigawatt peak power. Read More

Philos Trans A Math Phys Eng Sci 2019 Apr;377(2143):20180214

2 Physikalisch-Astronomische Fakultät, Friedrich-Schiller-Universität Jena, 07743 Jena , Germany.

A generalized theory of nucleation and growth of crystals in a metastable (supercooled or supersaturated) liquid is developed taking into account two principal effects: the diffusion mechanism of the particle-size distribution function in the space of particle radii and the unsteady-state growth rates of individual crystals induced by fluctuations in external temperature or concentration field. A system of the Fokker-Planck and balance integro-differential equations is formulated and analytically solved in a parametric form for arbitrary nucleation kinetics and arbitrary growth rates of individual crystals. The particle-size distribution function and system metastability are found in an explicit form. Read More

Philos Trans A Math Phys Eng Sci 2018 Feb;376(2113)

Department of Theoretical and Mathematical Physics, Laboratory of Multi-Scale Mathematical Modeling, Ural Federal University, Ekaterinburg 620000, Russian Federation.

The boundary integral method for propagating solid/liquid interfaces is detailed with allowance for the thermo-solutal Stefan-type models. Two types of mass transfer mechanisms corresponding to the local equilibrium (parabolic-type equation) and local non-equilibrium (hyperbolic-type equation) solidification conditions are considered. A unified integro-differential equation for the curved interface is derived. Read More

Philos Trans A Math Phys Eng Sci 2018 Feb;376(2113)

Department of Theoretical and Mathematical Physics, Laboratory of Multi-Scale Mathematical Modelling, Ural Federal University, Ekaterinburg, 620000, Russian Federation.

Motivated by important applications in materials science and geophysics, we consider the steady-state growth of anisotropic needle-like dendrites in undercooled binary mixtures with a forced convective flow. We analyse the stable mode of dendritic evolution in the case of small anisotropies of growth kinetics and surface energy for arbitrary Péclet numbers and -fold symmetry of dendritic crystals. On the basis of solvability and stability theories, we formulate a selection criterion giving a stable combination between dendrite tip diameter and tip velocity. Read More

Philos Trans A Math Phys Eng Sci 2018 Feb;376(2113)

Department of Theoretical and Mathematical Physics, Laboratory of Multi-Scale Mathematical Modeling, Ural Federal University, Ekaterinburg 620000, Russian Federation.

Transport processes around phase interfaces, together with thermodynamic properties and kinetic phenomena, control the formation of dendritic patterns. Using the thermodynamic and kinetic data of phase interfaces obtained on the atomic scale, one can analyse the formation of a single dendrite and the growth of a dendritic ensemble. This is the result of recent progress in theoretical methods and computational algorithms calculated using powerful computer clusters. Read More

Philos Trans A Math Phys Eng Sci 2018 Feb;376(2113)

Otto-Schott-Institut für Materialforschung, Physikalisch-Astronomische Fakultät, Friedrich-Schiller-Universität Jena, 07743 Jena, Germany

Phase-field analysis for the kinetic transition in an ordered crystal structure growing from an undercooled liquid is carried out. The results are interpreted on the basis of analytical and numerical solutions of equations describing the dynamics of the phase field, the long-range order parameter as well as the atomic diffusion within the crystal/liquid interface and in the bulk crystal. As an example, the growth of a binary AB crystal is described, and critical undercoolings at characteristic changes of growth velocity and the long-range order parameter are defined. Read More

Philos Trans A Math Phys Eng Sci 2018 Feb;376(2113)

Physikalisch-Astronomische Fakultät, Friedrich-Schiller-Universität Jena, 07743 Jena, Germany.

In standard descriptions, the master equation can be obtained by coarse-graining with the application of the hypothesis of full local thermalization that is equivalent to the local thermodynamic equilibrium. By contrast, fast transformations proceed in the absence of local equilibrium and the master equation must be obtained with the absence of thermalization. In the present work, a non-Markovian master equation leading, in specific cases of relaxation to local thermodynamic equilibrium, to hyperbolic evolution equations for a binary alloy, is derived for a system with two order parameters. Read More

Philos Trans A Math Phys Eng Sci 2018 Feb;376(2113)

Department of Theoretical and Mathematical Physics, Laboratory of Multi-Scale Mathematical Modeling, Ural Federal University, Ekaterinburg, 620000, Russian Federation.

The dynamics of the diffuse interface between liquid and solid states is analysed. The diffuse interface is considered as an envelope of atomic density amplitudes as predicted by the phase-field crystal model (Elder 2004 , 051605 (doi:10.1103/PhysRevE. Read More

ChemMedChem 2016 Jan 1;11(2):154-65. Epub 2015 Jul 1.

Department of Chemistry and Biochemistry and BioFrontiers Institute, University of Colorado, Boulder, CO, 80309-0596, USA.

Toll-like receptors (TLRs) have been shown to play an important role in the immune system, which warrants study of their remarkable potential as pharmacological targets. Activation of TLRs requires participation from specific pathogen-associated molecular patterns (PAMPs) and accessory proteins such as myeloid differentiation protein 2 (MD2), lipopolysaccharide binding protein (LBP), and cluster differentiation antigen 14 (CD14). Assembly of the TLR4-MD2-LPS complex is essential in TLR4 activation. Read More

Zentralbl Chir 2015 Apr 17;140(2):170-8. Epub 2013 Dec 17.

Lehrstuhl für Materialwissenschaft, Physikalisch-Astronomische Fakultät, Jena, Germany.

Background: Certain coatings such as titanium may improve the biocompatibility of hernia meshes. The coating with biopolymers such as polyethylenimine (PEI) can also improve the material characteristics of implants. This approach has, however, not yet been explored. Read More

Phys Rev E Stat Nonlin Soft Matter Phys 2013 Jul 26;88(1):013310. Epub 2013 Jul 26.

Friedrich-Schiller-Universität Jena, Physikalisch-Astronomische Fakultät, D-07737 Jena, Germany.

The phase-field crystal model (PFC model) resolves systems on atomic length scales and diffusive time scales and lies in between standard phase-field modeling and atomistic methods. More recently a hyperbolic or modified PFC model was introduced to describe fast (propagative) and slow (diffusive) dynamics. We present a finite-element method for solving the hyperbolic PFC equation, introducing an unconditionally stable time integration algorithm. Read More

Opt Express 2012 Feb;20(5):5601-6

Institut für Optik und Quantenelektronik, Physikalisch-Astronomische Fakultät ,Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, D-07743 Jena, Germany.

In this work we show that it is possible to increase the high-order harmonic yield when using wavefront-shaped laser beams. The investigation of the beam profile near the interaction region shows that the optimized beam is asymmetric and has a larger diameter. Thus, the optimized beam leads to a higher yield even if the peak intensity is lower compared to an unoptimized beam. Read More

Phys Rev Lett 2010 Jun 2;104(22):226403. Epub 2010 Jun 2.

Friedrich-Schiller-Universität Jena, Physikalisch-Astronomische Fakultät, Institut für Festkörperphysik, Max-Wien-Platz 1, D-07743 Jena, Germany.

We observe variable-range hopping conduction in thermal admittance spectroscopy and develop a method to evaluate the signal under this condition. As a relevant example of demonstration we employ Cu(In,Ga)(Se,S)2 thin-film solar cells and show that the fundamental N1 signal, which has been discussed for more than a decade in terms of minority carrier traps, does not display trap parameters, but is generated by the freezing-out of carrier mobility with decreasing temperature when hopping conduction prevails. This effect offers a new approach to carrier hopping and to semiconductors suffering from small mobility. Read More

Opt Lett 2009 Oct;34(19):3020-2

Physikalische Astronomische Fakultät, Friedrich-Schiller-Universität, Max-Wien-Platz 1, D-07743, Jena, Germany.

By means of a time-resolved, shadowgraphic method we observed directly the development of the pulse-splitting dynamics of a femtosecond laser pulse propagating in the filamentary regime in water. For the first time to our knowledge, the relative splitting velocity was measured. We compare the experimental data with numerical simulations. Read More

Biosci Biotechnol Biochem 1995 Jun;59(6):1044-7

Physikalisch-Astronomische-Technikwissenschaftliche Fakultät, Institut für Optik und Quantenelektronik, Friedrich-Schiller-Universität, Jena, Germany.

Photothermal signals from some biological materials exposed to modulated CO2 laser radiation were detected using the concept of photothermal interferometry. The magnitude and a phase of the signals were found to contain qualitative information about subsurface structural changes and variations of moisture content. Read More

Solid State Nucl Magn Reson 1992 Dec;1(5):261-6

Friedrich-Schiller-Universität Jena, Physikalisch-Astronomische Fakultät, Institut für Optik und Quantenelektronik, Germany.

27Al NMR spectra of polycrystalline aluminum borate 9Al2O3.2B2O3 have been measured at 104, 130 and 156 MHz. The parameters of the quadrupole interaction and the isotropic chemical shifts have been obtained by fitting the CT/MAS pattern and consideration of the inner satellite transitions m = 3/2<-->1/2 and m = - 1/2<-->- 3/2. Read More