Browsing by Subject "Hydrodynamics"

Now showing 1 - 9 of 9

Open Access
Archimedes' principle as an application of the divergence theorem
(Institute of Electrical and Electronics Engineers, 1990) Altintas, A.
A derivation is provided that allows one to obtain Archimedes' principle as an application of the divergence theorem.
Open Access
Biocompatibility studies on lanthanum oxide nanoparticles
(Royal Society of Chemistry, 2015) Brabu, B.; Haribabu, S.; Revathy, M.; Anitha, S.; Thangapandiyan, M.; Navaneethakrishnan, K. R.; Gopalakrishnan, C.; Murugan, S. S.; Kumaravel, T. S.
Lanthanum oxide nanoparticles (LONP), a rare earth metal oxide, have unique properties that make them a suitable candidate for several biomedical applications. We investigated certain key in vitro and in vivo biocompatibility endpoints on LONP. LONP were cytotoxic in in vitro assays and predominantly exerted their action via release of reactive oxygen species. These nanoparticles were neither irritants nor sensitizers in a rabbit model. LONP extracts did not exert any acute systemic toxicity effects in mice. On the other hand LONP exerted toxicity to the liver following oral administration, suggesting that these particles are absorbed from the gastrointestinal (GI) tract and deposited in the hepatobiliary system. LONP did not induce any mutation in the Ames test both in the presence or absence of S-9. These observations provide a base line biocompatibility and toxicity data on LONP. The current findings will also be useful in defining standards for nanoparticle containing devices. © The Royal Society of Chemistry.
Open Access
Homogenization-based design of surface textures in hydrodynamic lubrication
(John Wiley and Sons Ltd, 2016) Waseem, A.; Temizer, İ.; Kato, J.; Terada, K.
An optimization framework is developed for surface texture design in hydrodynamic lubrication. The microscopic model of the lubrication interface is based on the Reynolds equation, and the macroscopic response is characterized through homogenization. The microscale setting assumes a unilateral periodic texture but implicitly accounts for the bilateral motion of the surfaces. The surface texture in a unit cell is described indirectly through the film thickness, which is allowed to vary between prescribed minimum and maximum values according to a morphology variable distribution that is obtained through the filtering of a design variable. The design and morphology variables are discretized using either element-wise constant values or through first-order elements. In addition to sharp textures, which are characterized by pillars and holes that induce sudden transitions between extreme film thickness values, the framework can also attain a variety of non-standard smoothly varying surface textures with a macroscopically isotropic or anisotropic response. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.
Open Access
Hydrodynamic approach for modelling transport in quantum well device structures
(Institute of Physics Publishing Ltd., 1998) Besikci, C.; Tanatar, Bilal; Sen, O.
A semiclassical approach for modelling electron transport in quantum well structures is presented. The model is based on the balance equations governing the conservation of particle density, momentum and energy with Monte Carlo (MC) generated transport parameters. Three valleys of the conduction band, size quantization in the Γ valley, and the lowest two subbands in the quantum well are considered by taking the detailed intersubband dynamics into account. The transport parameters of the model are extracted from steady-state MC simulations based on an improved formulation of two-dimensional polar optical phonon scattering including screening effects. The predictions of the proposed model have been found to be in excellent agreement with those of the ensemble MC simulations under both time varying and spatially nonuniform fields. The calculated transport parameters which are of interest for device modelling are presented as a function of the electron energy for the AIGaAs/GaAs quantum well. The model serves as an accurate semiclassical alternative to costly ensemble MC simulations for studying the transport in quantum well structures and for the modelling and optimization of submicron devices based on these structures, such as modulation doped field-effect transistors (MODFETs).
Open Access
Integrability and Poisson structures of three dimensional dynamical systems and equations of hydrodynamic type
(1992) Gümral, Hasan
We show that the Poisson structure of completely integrable 3 dimensional dynamical systems can be defined in terms of an integrable 1-form. We shall take advantage of this fact and use the theory of foliations in discussing the geometrical structure underlying complete and partial integrability. Techniques for finding Poisson structures are presented and applied to various examples such as the Halphen system which has been studied as the two monopole problem by Atiyah and Hitchin. We shall show that the Halphen system can be formulated in terms of a flat SL{2, /i)-valued connection and belongs to a non-trivial GodbillonVey class. On the other hand, for the Euler top and a special case of 3- species Lotka-Volterra equations which are contained in the Halphen system as limiting cases, this structure degenerates into the form of globally integrable biHamiltonian structures. The globally integrable bi-Hamiltonian case is a linear and the sb structure is a quadratic unfolding of an integrable 1-form in 3 -f 1 dimensions. We shall show that the existence of a vector field compatible with the flow is a powerful tool in the investigation of Poisson structure and present some new techniques for incorporating arbitrary constants into the Poisson 1- form. This leads to some extensions, analoguous to q-extensions, of Poisson structure. We shall find that the Kermack-McKendrick model and some of its generalizations describing the spread of epidemics as well as the integrable cases of the Lorenz, Lotka-Volterra, May-Leonard and Maxwell-Bloch systems admit globally integrable bi-Hamiltonian structure. In the second part, we complete the discussion of the Hamiltonian structure of 2-component equations of hydrodynamic type by presenting the Hamiltonian operators for Euler’s equation governing the motion of plane sound waves of finite amplitude and another quasi-linear second order wave equation. There exists a doubly infinite family of conserved Hamiltonians for the equations of gas dynamics which degenerate into one, namely the Benney sequence, for shallow water waves. We present further infinite sequences of conserved quantities for these equations. In the case of multi-component equations of hydrodynamic type, we show that Kodama’s generalization of the shallow water equations admits bi-Hamiltonian structure. We present a simple way of constructing the second Hamiltonian operators for N-component equations admitting some scaling properties. Using dimensional analysis we are led to an Ansatz for both the Hamiltonian operator as well as the conserved quantities in terms of ratios of polynomials. The coefficients of these polynomials are determined from the Jacobi identities. The resulting bi-Hamiltonian structure of Kodama equations consists of generalization of the Cavalcante-McKean’s work for the shallow water waves. The Kodama reduction of the dispersionless-Boussinesq equations and the Lax reduction of the Benney moment equations are shown to be equivalent by a symmetry transformation. They can be cast into the form of a triplet of conservation laws which enable us to recognize a non-trivial scaling symmetry. The choice of the Hamiltonian density lor the second Hamiltonian structure is a crucial step and the analysis of recursion relations becomes necessary. The resulting bi-Hamiltonian structure generates three infinite sequences of conserved densities.
Open Access
Ionic current inversion in pressure-driven polymer translocation through nanopores
(American Physical Society, 2015) Buyukdagli, S.; Blossey, R.; Ala-Nissila, T.
We predict streaming current inversion with multivalent counterions in hydrodynamically driven polymer translocation events from a correlation-corrected charge transport theory including charge fluctuations around mean-field electrostatics. In the presence of multivalent counterions, electrostatic many-body effects result in the reversal of the DNA charge. The attraction of anions to the charge-inverted DNA molecule reverses the sign of the ionic current through the pore. Our theory allows for a comprehensive understanding of the complex features of the resulting streaming currents. The underlying mechanism is an efficient way to detect DNA charge reversal in pressure-driven translocation experiments with multivalent cations. © 2015 American Physical Society.
Open Access
Sensing translocating polymers via induced magnetic fields
(TÜBİTAK, 2023) Büyükdağlı, Şahin
The requirement to boost the resolution of nanopore-based biosequencing devices necessitates the integration of novel biosensing techniques with reduced sensitivity to background noise. In this article, we probe the signatures of translocating polymers in magnetic fields induced by ionic currents through membrane nanopores. Within the framework of a previously introduced charge transport theory, we evaluate the magnetic field signals generated by voltage- and pressure-driven DNA translocation events in monovalent salt solutions. Our formalism reveals that in voltage-driven transport, the translocating polymer suppresses the induced magnetic field via the steric blockage of the ion current through the midpore. In the case of pressure-driven transport, the magnetic field reduction by translocation originates from the negative electrokinetic contribution of the anionic DNA surface charges to the streaming current predominantly composed of salt cations. The magnitude of the corresponding field signals is located in the nano-Tesla range covered by the resolution of the magnetoelectric sensors able to detect magnetic fields down to the pico-Tesla range. This suggests that the integration of magnetic field detection techniques into the current biosequencing approaches can complement efficiently the conventional biosensing strategies employing ionic current readouts with high susceptibility to background noise.
Open Access
A simple approach for the fabrication of 3D microelectrodes for impedimetric sensing
(Institute of Physics Publishing, 2015) Guler, M. T.; Bilican, I.; Agan, S.; Elbuken, C.
In this paper, we present a very simple method to fabricate three-dimensional (3D) microelectrodes integrated with microfluidic devices. We form the electrodes by etching a microwire placed across a microchannel. For precise control of the electrode spacing, we employ a hydrodynamic focusing microfluidic device and control the width of the etching solution stream. The focused widths of the etchant solution and the etching time determine the gap formed between the electrodes. Using the same microfluidic device, we can fabricate integrated 3D electrodes with different electrode gaps. We have demonstrated the functionality of these electrodes using an impedimetric particle counting setup. Using 3D microelectrodes with a diameter of 25 μm, we have detected 6 μm-diameter polystyrene beads in a buffer solution as well as erythrocytes in a PBS solution. We study the effect of electrode spacing on the signal-to-noise ratio of the impedance signal and we demonstrate that the smaller the electrode spacing the higher the signal obtained from a single microparticle. The sample stream is introduced to the system using the same hydrodynamic focusing device, which ensures the alignment of the sample in between the electrodes. Utilising a 3D hydrodynamic focusing approach, we force all the particles to go through the sensing region of the electrodes. This fabrication scheme not only provides a very low-cost and easy method for rapid prototyping, but which can also be used for applications requiring 3D electric field focused through a narrow section of the microchannel.
Open Access
Tkachenko modes of the square vortex lattice in a two-component Bose-Einstein condensate
(2006) Keçeli, Murat; Öktel, M. Özgür
We study Tkachenko modes of the square vortex lattice of a two-component Bose-Einstein condensate (BEC) in the mean-field quantum Hall regime, considering the coupling of these modes with density excitations. We derive the hydrodynamic equations and obtain the dispersion relations of the excitation modes. We find that there are two types of excitations, gapped inertial modes and gapless Tkachenko modes. These modes have two branches which we call acoustic and optical modes in analogy with phonons. The former has quadratic while the latter has linear wave-number dependence in both inertial and Tkachenko modes. Acoustic Tkachenko mode is found to be anisotropic while the other three modes are isotropic. The anisotropy of the acoustic Tkachenko mode reflects the four-fold symmetry of the square lattice.