@misc{BorciaMenzelBestehornetal., author = {Borcia, Rodica and Menzel, Stefan and Bestehorn, Michael and Karpitschka, Stefan and Riegler, Horst}, title = {Delayed coalescence of droplets with miscible liquids: Lubrication and phasefield theories}, series = {European Physical Journal E}, volume = {34}, journal = {European Physical Journal E}, number = {3}, issn = {1292-8941}, pages = {11024-9}, language = {en} } @misc{ReifVarlamovaVarlamovetal., author = {Reif, J{\"u}rgen and Varlamova, Olga and Varlamov, Sergej and Bestehorn, Michael}, title = {The role of asymmetric excitation in self-organized nanostructure formation upon femtosecond laser ablation}, series = {Applied Physics / A}, volume = {104}, journal = {Applied Physics / A}, number = {3}, issn = {1432-0630}, pages = {969 -- 973}, language = {en} } @misc{VarlamovaReifVarlamovetal., author = {Varlamova, Olga and Reif, J{\"u}rgen and Varlamov, Sergej and Bestehorn, Michael}, title = {The laser polarization as control parameter in the formation of laser-induced periodic surface structures: Comparison of numerical and experimental results}, series = {Applied Surface Science}, volume = {257}, journal = {Applied Surface Science}, number = {12}, issn = {0169-4332}, pages = {5465 -- 5469}, language = {en} } @misc{BorciaBestehorn, author = {Borcia, Rodica and Bestehorn, Michael}, title = {Numerical simulations on delayed coalescence of droplets in confinedgeometries}, language = {en} } @misc{BorciaBestehorn, author = {Borcia, Ion-Dan and Bestehorn, Michael}, title = {Simulation of pattern morphology in binary liquid mixtures}, language = {en} } @inproceedings{BorciaBestehornEgbers, author = {Borcia, Rodica and Bestehorn, Michael and Egbers, Christoph}, title = {Surface effects at the mixing of two perfectly miscible components in a thin liquid film}, series = {International Topical Team Workshop on Two-Phase Systems for Ground and Space Applications, ITTW 2013}, booktitle = {International Topical Team Workshop on Two-Phase Systems for Ground and Space Applications, ITTW 2013}, language = {en} } @inproceedings{BorciaBorciaBestehornetal., author = {Borcia, Ion-Dan and Borcia, Rodica and Bestehorn, Michael and Egbers, Christoph}, title = {Drops on cylindrical wires}, series = {International Topical Team Workshop on Two-Phase Systems for Ground and Space Applications, ITTW 2013}, booktitle = {International Topical Team Workshop on Two-Phase Systems for Ground and Space Applications, ITTW 2013}, language = {en} } @inproceedings{BorciaBorciaBestehornetal., author = {Borcia, Ion-Dan and Borcia, Rodica and Bestehorn, Michael and Borcia, C. and Dumitrascu, N. and Egbers, Christoph}, title = {Drops on cylindrical surfaces}, series = {7th Conference of the International Marangoni Association, Vienna (Austria), June 23-26, 2014}, booktitle = {7th Conference of the International Marangoni Association, Vienna (Austria), June 23-26, 2014}, publisher = {Techn. Univ.}, address = {Vienna}, pages = {S. 33}, language = {en} } @inproceedings{ReifVarlamovaVarlamovetal., author = {Reif, J{\"u}rgen and Varlamova, Olga and Varlamov, Sergej and Bestehorn, Michael}, title = {The role of asymmetric excitation in self-organized nanostructure formation upon femtosecondlaser ablation}, series = {International Symposium on High Power Laser Ablation 2012, Santa Fe, New Mexico, USA, 30 April - 3 May 2012}, booktitle = {International Symposium on High Power Laser Ablation 2012, Santa Fe, New Mexico, USA, 30 April - 3 May 2012}, editor = {Phipps, Claude R.}, publisher = {American Institute of Physics}, address = {Melville, NY}, isbn = {978-0-7354-1068-8}, pages = {428 -- 441}, language = {en} } @misc{VarlamovaReifVarlamovetal., author = {Varlamova, Olga and Reif, J{\"u}rgen and Varlamov, Sergej and Bestehorn, Michael}, title = {Modeling of the Laser Polarization as Control Parameter in Self-Organized Surface Pattern}, series = {Journal of Nanoscience and Nanotechnology}, volume = {11}, journal = {Journal of Nanoscience and Nanotechnology}, number = {10}, issn = {1533-4880}, pages = {9274 -- 9281}, language = {en} } @misc{VarlamovaCostacheReifetal., author = {Varlamova, Olga and Costache, Florenta Adriana and Reif, J{\"u}rgen and Bestehorn, Michael}, title = {Self-organized pattern formation upon femtosecond laser ablation by circular polarized light}, series = {Applied Surface Science}, volume = {252}, journal = {Applied Surface Science}, number = {13}, issn = {0169-4332}, pages = {4702 -- 4706}, language = {en} } @inproceedings{ReifCostacheEckertetal., author = {Reif, J{\"u}rgen and Costache, Florenta Adriana and Eckert, Sebastian and Kouteva-Arguirova, Simona and Bestehorn, Michael and Georgescu, Ionut and Semorek, A. F. and Martin, P. and Gobert, O. and Seifert, Winfried}, title = {Formation of self-organized regular nanostructures upon femtosecond laser ablation}, series = {Fifth International Symposium on Laser Precision Microfabrication, 11 - 14 May, 2004, Nara, Japan}, booktitle = {Fifth International Symposium on Laser Precision Microfabrication, 11 - 14 May, 2004, Nara, Japan}, publisher = {SPIE}, address = {Bellingham, Wash.}, isbn = {0-8194-5623-3}, pages = {S. 737}, language = {en} } @incollection{VarlamovaReifVarlamovetal., author = {Varlamova, Olga and Reif, J{\"u}rgen and Varlamov, Sergej and Bestehorn, Michael}, title = {Self-organized Surface Patterns Originatin from Laser-Induced Instability}, series = {Progress in nonlinear nano-optics}, booktitle = {Progress in nonlinear nano-optics}, editor = {Sakabe, Shuji and Lienau, Christoph and Grunwald, R{\"u}diger}, publisher = {Springer}, address = {Cham [u.a.]}, isbn = {978-3-319-12216-8}, pages = {3 -- 29}, language = {en} } @misc{ChengBestehornFiroozabadi, author = {Cheng, Philip and Bestehorn, Michael and Firoozabadi, Abbas}, title = {Effect of permeability anisotropy on density-driven flow for CO2 sequestration in saline aquifers}, series = {Water Resources Research}, volume = {48}, journal = {Water Resources Research}, number = {9}, issn = {1944-7973}, doi = {10.1029/2012WR011939}, pages = {W09539}, abstract = {Solubility trapping of carbon dioxide (CO2) in deep saline aquifers is considered one of the most effective methods for carbon sequestration. Dissolution of CO2 into the brine may create gravitational instabilities that lead to the onset of convection, which greatly enhances the storage efficiency and reduces the possibilities of leakage. Convection appears in the form of downward traveling fingers of relatively dense, CO2-dissolved fluid. Many natural aquifer formations display considerable permeability anisotropy, where the horizontal permeability kh may be several times greater than the vertical permeability kz. It has been previously found that increasing kh for a fixed kz reduces the critical time tc at which onset occurs and the critical wavelength λc with which the fingers initially form. We extend earlier work by showing how and why this occurs. Our results reveal new insights about λc. We have studied the behavior for times greater than tc using high-resolution numerical simulations. We show that the enhanced dissolution from convection can become significant much earlier in anisotropic media. Furthermore, the effects of anisotropy may be sustained for a long period of time. Our results suggest that permeability anisotropy can allow a wider range of aquifer formations to be considered for effective sequestration.}, language = {en} } @misc{BestehornFiroozabadi, author = {Bestehorn, Michael and Firoozabadi, Abbas}, title = {Effect of fluctuations on the onset of density-driven convection in porous media}, series = {Physics of Fluids}, volume = {24}, journal = {Physics of Fluids}, number = {11}, issn = {1089-7666}, doi = {10.1063/1.4767467}, pages = {114102}, abstract = {We study the dissolution of CO2 in saline aquifers. The long diffusion times can be accelerated by orders of magnitude from mass transfer that origins from convection.Convection occurs at a critical time via a phase transition from the horizontally homogeneous diffusion state. To start the instability, perturbations that break the horizontal translation symmetry are necessary. We start with the basic equations and the boundary conditions, examine the linearized equations around the diffusive time and z-dependent base state and compare different definitions of the critical time found in the literature. Taking a simple model we show the role of fluctuations for delayed instabilities if the control parameter is slowly swept through the bifurcation point. Apart from the critical time we use a "visible" time where convection is manifested in the vertical CO2 transport. We specify the perturbations with respect to their strength and length scale, and compute the critical times for various cases by numerical integration of the basic equations in two spatial dimensions. Fluctuating concentration at the upper boundary, fluctuating porosity as well fluctuating permeability are studied in detail. For the permeability fluctuation, the compressibility of the fluid becomes important and the velocity field cannot be derived from a stream function. Our work also includes non-isothermal conditions with a prescribed vertical geothermal gradient and space dependent thermal conductivity. Temperature fields for different standard configurations are computed numerically and serve as starting condition for density-driven convection. Based on our work, we conclude that the visible time is much larger than the critical time. The visible time is a strong function of strength and length scale of the perturbations.}, language = {en} } @misc{ReifVarlamovaUhligetal., author = {Reif, J{\"u}rgen and Varlamova, Olga and Uhlig, Sebastian and Varlamov, Sergej and Bestehorn, Michael}, title = {On the physics of self-organized nanostructure formation upon femtosecond laser ablation}, series = {Applied Physics A}, volume = {117}, journal = {Applied Physics A}, number = {1}, issn = {0947-8396}, doi = {10.1007/s00339-014-8339-x}, pages = {179 -- 184}, abstract = {We present new results on femtosecond LIPSS on silicon, fostering the dynamic model of self-organized structure formation. The first set of experiments demonstrates LIPSS formation by irradiation with a femtosecond white light continuum. The ripples are, as usual, perpendicular to the light polarization with a fluence-dependent wavelength between 500 and 700 nm. At higher dose (fluence × number of shots), the LIPSS turn to much coarser structures. The second set of experiments displays the dose dependence of pattern evolution at about threshold fluence. In contrast to the general case of multi-pulse LIPSS, where a strong dependence of the structures on the laser polarization is observed, single-shot exposition of silicon at about the ablation threshold results in a concentric pattern of very regular sub-wavelength ripples following the oval shape of the irradiated spot, without any reference to the laser polarization. When increasing the number of pulses, the usual, typical ripples develop and then coalesce into broader perpendicular structures, interlaced with remnants of the first, finer ripples.}, language = {en} } @misc{Bestehorn, author = {Bestehorn, Michael}, title = {Laterally Extended Thin Liquid Films with inertia Under External Vibrations}, series = {Physics of Fluids}, volume = {25}, journal = {Physics of Fluids}, number = {11}, issn = {1089-7666}, doi = {10.1063/1.4830255}, pages = {114106}, abstract = {We consider thin liquid films on a horizontal, solid, and completely wetting substrate. The substrate is subjected to oscillatory accelerations in the normal direction and/or in the horizontal direction. A linear Floquet analysis shows that the planar film surface loses stability if amplitudes and frequencies of the harmonic oscillations meet certain criteria. Based on the long wave lubrication approximation, we present an integral boundary layer model where the z component is integrated out and the spatial dimension is reduced by one. The linear stability analysis of this model shows good agreement with the exact problem and with the linearized long wave equations. Pattern formation in the nonlinear regime is computed numerically from the long wave model in two and three spatial dimensions. Normal oscillations show the traditional Faraday patterns such as squares and hexagons. Lateral oscillations cause a pattern formation scenario similar to spinodal dewetting, namely coarsening and no rupture. For certain amplitude and frequency ranges, combined lateral and normal oscillations can give rise to one or more traveling drops. Finally, we discuss the control of a drop's motion in the horizontal plane.}, language = {en} } @misc{BestehornHanOron, author = {Bestehorn, Michael and Han, Qi and Oron, Alexander}, title = {Nonlinear Pattern Formation in Thin Liqiud Films Under External Vibrations}, series = {Physical Review E}, volume = {88}, journal = {Physical Review E}, number = {2}, issn = {2470-0053}, doi = {10.1103/PhysRevE.88.023025}, pages = {023025}, abstract = {We study a thin liquid film with a free surface on a planar horizontal substrate. The substrate is subjected to oscillatory accelerations in the normal and/or in the horizontal direction(s). The description is based on the longwave approximation including inertia effects, which are important due to the large velocities imparted by external vibrations. The linearized system is examined using the Floquet analysis. Pattern formation in the nonlinear regime is computed numerically from the longwave equations for the thickness and the flow rate of the fluid in two and in three spatial dimensions. For certain amplitude and frequency ranges, combined lateral and normal oscillations can give rise to one or more traveling drops, similar to recent experimental findings by Brunet et al. [Phys. Rev. Lett. 99, 144501 (2007)].}, language = {en} } @misc{Bestehorn, author = {Bestehorn, Michael}, title = {Regular Hexagons and Stripes on Marangoni and Rayleigh-Taylor unstable volatile thin films}, series = {European Journal of Mechanics - B/Fluids}, volume = {47}, journal = {European Journal of Mechanics - B/Fluids}, doi = {10.1016/j.euromechflu.2013.12.005}, pages = {48 -- 56}, abstract = {Thin volatile Newtonian liquid films with a free surface on a cooled horizontal substrate are studied theoretically and numerically. We show that if the fluid is initially in equilibrium with its own vapor in the gas phase, regular surface deformation patterns in the form of long-wave hexagons or stripes having a well defined lateral length scale are observed, depending on the instability mechanism. This is different to the case without evaporation where rupture or coarsening to larger and larger spatially disordered patterns is seen in the long time limit. We propose to use such a system to create a regular structuring of the film's surface. Heat production by latent heat and the influence of a temperature dependent surface tension (Marangoni effect) are included as well. Special emphasis is laid on the so-called anomalous Marangoni effect. In this case a parameter region where stripes should occur already at threshold is found by means of a systematic weakly non-linear analysis.}, language = {en} } @misc{BorciaBorciaBestehorn, author = {Borcia, Rodica and Borcia, Ion-Dan and Bestehorn, Michael}, title = {Nonlinear dynamics of thin liqiud films consisting of two miscible components}, series = {Physical Review E}, volume = {86}, journal = {Physical Review E}, number = {5}, issn = {2470-0053}, doi = {10.1103/PhysRevE.86.056319}, pages = {056319}, abstract = {Recently, we systematically derived a system of two coupled conservation equations governing a thin liquid layer with a deformable surface composed of two completely miscible components [Phys. Fluids 22, 104102 (2010)]. One equation describes the location of the free surface and the second one the evolution of the mean concentration. This lubrication model was investigated previously in linearized form. The study is now extended to the fully nonlinear case of thin liquid films of a binary mixture (in one and two horizontal spatial dimensions) with and without heat transport. For an initially flat and motionless film heated from below, we analyze the component separation induced by the Soret effect. Nonlinear simulations show that the Soret effect can cause a multitude of interesting behaviors, such as oscillatory patterns and solitonlike structures (localized traveling drops or holes). A stronger component separation induced by stronger Soret effects favors faster-moving localized structures. For isothermal systems, we study the fusion and the mixing of two thin liquid films of different but perfectly miscible liquids. Marangoni-driven forces can cause delayed coalescence, ripple formation, and fingering patterns at the borderline between the two liquid layers. A systematic analysis for ripple pattern formation and finger instabilities at different diffusion constants shows that these phenomena appear more pronounced for lower diffusion in the system.}, language = {en} } @misc{BorciaBestehorn, author = {Borcia, Rodica and Bestehorn, Michael}, title = {Partial coalescence of sessile drops with different miscible liquids}, series = {Langmuir}, volume = {29}, journal = {Langmuir}, number = {14}, issn = {1520-5827}, doi = {10.1021/la3050835}, pages = {4426 -- 4429}, abstract = {Using computer simulations in three spatial dimensions, we examine the interaction between two deformable drops consisting of two perfectly miscible liquids sitting on a solid substrate under a given contact angle. Driven by capillarity and assisted by Marangoni effects at the droplet interfaces, several distinct coalescence regimes are achieved after the droplets' collision.}, language = {en} } @misc{BorciaBestehorn, author = {Borcia, Rodica and Bestehorn, Michael}, title = {A phase field description of self-propulsion of twin sessile drops induced by surface tension gradients}, series = {Fluid Dynamics Research}, volume = {46}, journal = {Fluid Dynamics Research}, number = {4}, issn = {0169-5983}, doi = {10.1088/0169-5983/46/4/041405}, pages = {041405}, abstract = {We describe the self-propulsion of two sessile drops induced by surface tension gradients at the droplet interfaces using a three-dimensional phase field model. We study the problem for the low viscosity regime when the width of the connecting neck between the interacting drops increases linearly with increasing t1/2 and the merger is dominated by capillary forces. We investigate the dependence of the displacement achieved by self-propulsion on viscous shearing as well as the internal flow structure during the coalescence process.}, language = {en} } @misc{BorciaBestehorn, author = {Borcia, Rodica and Bestehorn, Michael}, title = {Phase field modelling of non-equilibrium patterns on the surface of a liquid film under lateral oscillations at the substrate}, series = {International Journal of Bifurcation and Chaos}, volume = {24}, journal = {International Journal of Bifurcation and Chaos}, number = {9}, issn = {0218-1274}, doi = {10.1142/S0218127414501107}, pages = {1450110}, abstract = {We use a phase field model which couples the generalized Navier-Stokes equation (including the Korteweg stress tensor) with the continuity equation for studying nonlinear pattern formation on the surface of a liquid film under (linear and circular) lateral harmonic vibrations at the solid substrate. First, we prove the thermodynamic consistency of our phase field model. Next, we present computer simulations in three spatial dimensions. We illustrate nonequilibrium patterns at the instability onset, confirming in this way the results recently reported in Phys. Rev. E 88, 023025 (2013). The lateral profiles of the deflected surface are compared with those reported in J. Fluid Mech. 686, 409 (2011) for Faraday instability excited by vertical harmonic vibrations at the bottom plate.}, language = {en} } @misc{BorciaBorciaBestehorn, author = {Borcia, Rodica and Borcia, Ion-Dan and Bestehorn, Michael}, title = {Can vibrations control drop motion?}, series = {Langmuir}, volume = {30}, journal = {Langmuir}, number = {47}, issn = {1520-5827}, doi = {10.1021/la503415r}, pages = {14113 -- 14117}, abstract = {We discuss a mechanism for controlled motion of drops with applications for microfluidics and microgravity. The mechanism is the following: a solid plate supporting a liquid droplet is simultaneously subject to lateral and vertical harmonic oscillations. In this way the symmetry of the back-and-forth droplet movement along the substrate under inertial effects is broken and thus will induce a net driven motion of the drop. We study the dependency of the traveled distance on the oscillation parameters (forcing amplitude, frequency, and phase shift between the two perpendicular oscillations) via phase field simulations. The internal flow structure inside the droplet is also investigated. We make predictions on resonance frequencies for drops on a substrate with a varying wettability.}, language = {en} } @misc{PototskyBestehorn, author = {Pototsky, Andrey and Bestehorn, Michael}, title = {Faraday instability of a two-layer liquid film with a free upper surface}, series = {Physical Review Fluids}, volume = {1}, journal = {Physical Review Fluids}, number = {2}, issn = {2469-990X}, doi = {10.1103/PhysRevFluids.1.023901}, pages = {023901-1 -- 023901-18}, abstract = {We study the linear stability of a laterally extended flat two-layer liquid film under the influence of external vertical vibration. The first liquid layer rests on a vibrating solid plate and is overlaid by a second layer of immiscible fluid with deformable upper surface. Surface waves, excited as the result of the Faraday instability, can be characterized by a time-dependent relative amplitude of the displacements of the liquid-liquid and the liquid-gas interfaces. The in-phase displacements are associated with a zigzag (barotropic) mode and the antiphase displacement corresponds to the varicose thinning mode. We numerically determine the stability threshold in the vibrated two-layer film and compute the dispersion relation together with the decay rates of the surface waves in the absence of vibration. The in-phase and the antiphase displacements are strongly coupled in the vibrated system. The interplay between the Faraday and the Rayleigh-Taylor instabilities in the system with heavier fluid on top of a lighter fluid is analyzed.}, language = {en} }