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Fernández, M. Laura, Marcelo Risk, Ramon Reigada, and P. Thomas Vernier. "Size-controlled nanopores in lipid membranes with stabilizing electric fields." Biochemical and Biophysical Research Communications 423, no. 2 (June 2012): 325–30. http://dx.doi.org/10.1016/j.bbrc.2012.05.122.
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El-Sayed, M. F., N. T. Eldabe, M. H. Haroun, and D. M. Mostafa. "Nonlinear Electrohydrodynamic Stability of Two Superposed Walters B′ Viscoelastic Fluids in Relative Motion Through Porous Medium." Journal of Mechanics 29, no. 4 (May 23, 2013): 569–82. http://dx.doi.org/10.1017/jmech.2013.36.
Повний текст джерелаАнотація:
ABSTRACTA nonlinear stability of two superposed semi-infinite Walters B′ viscoelastic dielectric fluids streaming through porous media in the presence of vertical electric fields in absence of surface charges at their interface is investigated in three dimensions. The method of multiple scales is used to obtain a Ginzburg-Landau equation with complex coefficients describing the behavior of the system. The stability of the system is discussed both analytically and numerically in linear and nonlinear cases, and the corresponding stability conditions are obtained. It is found, in the linear case, that the surface tension and medium permeability have stabilizing effects, and the fluid velocities, electric fields and kinematic viscoelastici-ties have destabilizing effects, while the porosity of porous medium and kinematic viscosities have dual role on the stability. In the nonlinear case, it is found that the fluid velocities, kinematic viscosities, kinematic viscoelasticities, surface tension and porosity of porous medium have stabilizing effects; while the electric fields and medium permeability have destabilizing effects.
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Papageorgiou, Demetrios T. "Film Flows in the Presence of Electric Fields." Annual Review of Fluid Mechanics 51, no. 1 (January 5, 2019): 155–87. http://dx.doi.org/10.1146/annurev-fluid-122316-044531.
Повний текст джерелаАнотація:
The presence of electric fields in immiscible multifluid flows induces Maxwell stresses at sharp interfaces that can produce electrohydrodynamic phenomena of practical importance. Electric fields can be stabilizing or destabilizing depending on their strength and orientation. In microfluidics, fields can be used to drive systems out of equilibrium to produce hierarchical patterning, mixing, and phase separation. We describe nonlinear theories of electrohydrodynamic instabilities in immiscible multilayer flows in several geometries, including flows over or inside planar or topographically structured substrates and channels and flows in cylinders and cylindrical annuli. Matched asymptotic techniques are developed for two- and three-dimensional flows, and reduced-dimension nonlinear models are derived and studied. When all regions are slender, electrostatic extensions to lubrication or shallow-wave theories are derived. In the presence of nonslender layers, nonlocal terms emerge naturally to modify the evolution equations. Analysis and computations provide a plethora of dynamics, including nonlinear traveling waves, spatiotemporal chaos, and singularity formation. Direct numerical simulations are used to evaluate the models and go beyond their range of validity to quantify phenomena such as electric field–induced directed patterning, suppression of Rayleigh–Taylor instabilities, and electrostatically induced pumping in microchannels. Comparisons of theory and simulations with available experiments are included throughout.
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Radwan, Ahmed E. "Electrogravitational instability of an annular fluid jet coaxial with a very dense fluid cylinder under radial varying fields." Journal of Plasma Physics 44, no. 3 (December 1990): 455–65. http://dx.doi.org/10.1017/s0022377800015300.
Повний текст джерелаАнотація:
The electrodynamic instability of a self-gravitating dielectric annular fluid jet possessing a very dense fluid (of negligible inertia) cylinder mantle surrounded by another dielectric self-gravitating medium pervaded by a radial varying electric field is investigated. A general eigenvalue relation valid for all possible symmetric m = 0 and asymmetric m ≠ 0 perturbation modes is derived and discussed. The electrodynamic force has a strong destabilizing influence not only to m = 0 but also to m ≠ 0 disturbance modes. The self-gravitational force is stabilizing to all pure m ≠ 0 modes, while to m = 0 it is stabilizing or destabilizing according to conditions. The destabilizing effects of the internal and exterior varying electric fields shrink the gravitationally stable states and simultaneously increase the unstable ones. The electrogravitodynamic instability character of the model can be minimized if the electrodynamic force effect is extremely small in comparison with that of the self-gravitational force, but the instability will never be suppressed.
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El-Sayed, Mohamed Fahmy. "Electrohydrodynamic Interfacial Stability Conditions in the Presence of Heat and Mass Transfer and Oblique Electric Fields." Zeitschrift für Naturforschung A 54, no. 8-9 (September 1, 1999): 470–76. http://dx.doi.org/10.1515/zna-1999-8-904.
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A novel mathematical formulation to deal with interfacial stability problems of the Kelvin-Helmholtz type with heat and mass transfer in the presence of oblique electric fields is presented. The perturbed system is composed of two homogeneous, inviscid, incompressible, dielectric, and streaming fluids sep-arated by a horizontal interface, and bounded by two rigid planes. The effect of a phase transition on the instability is considered, and the linear dispersion relations are obtained and discussed. It is found that the electric field has a major effect and can be chosen to stabilize or destabilize the flow. For Ray-leigh-Taylor instability problems of a liquid-vapor system it is found that the effect of mass and heat transfer enhances the stability of the system when the vapor is hotter than the liquid, although the clas-sical stability criterion is still valid. For Kelvin-Helmholtz instability problems, however, the classical stability criterion is found to be substantially modified due to the effects of the electric field, mass and heat transfer. A new stability condition relating the magnitude and orientation of the electric field and the dielectric constants is obtained. Oblique electric fields are found to have stabilizing effects which are reduced by the normal components of the electric fields. The effects of orientation of the electric fields and fluid depths on the stability configuration are also discussed.
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HOFFMAN, BRENDAN D., and ERIC S. G. SHAQFEH. "The effect of Brownian motion on the stability of sedimenting suspensions of polarizable rods in an electric field." Journal of Fluid Mechanics 624 (April 10, 2009): 361–88. http://dx.doi.org/10.1017/s0022112008005405.
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We examine the collective dynamics of polarizable, Brownian, sedimenting rods of high aspect ratio. Previous work of Koch and Shaqfeh (J. Fluids Mech., vol. 209, 1989 pp. 521–542) has shown that in the absence of Brownian motion, sedimenting suspensions of rods are unstable to concentration fluctuations and form dense streamers via interparticle hydrodynamic interactions. Recently, Saintillan, Shaqfeh & Darve (Phys. Fluids, vol. 18 (121701), 2006b p. 1) demonstrated that electric fields can act to stabilize these non-Brownian suspensions of polarizable rods through induced-charge electrokinetic rotation, which forces particle alignment. In this paper, we employ a mean-field linear stability analysis as well as Brownian dynamics simulations to study the effect of thermal motion on the onset of instability. We find that in the absence of electric fields, Brownian motion consistently suppresses instability formation through randomization of particle orientation. However, when electric fields are applied, thermal motion can act to induce instability by counteracting the stabilizing effect of induced-charge orientation.
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González, H., F. M. J. Mccluskey, A. Castellanos, and A. Barrero. "Stabilization of dielectric liquid bridges by electric fields in the absence of gravity." Journal of Fluid Mechanics 206 (September 1989): 545–61. http://dx.doi.org/10.1017/s0022112089002405.
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The stability of liquid bridges in zero gravity conditions under the influence of an a.c. electric field tangential to the interface is examined in this paper. For the theoretical study, a static analysis was carried out to find the bifurcation surfaces as a function of the three relevant non-dimensional parameters: Λ, the slenderness or ratio of height to diameter of the cylindrical bridge; β0, the ratio of dielectric constants of the two fluids used and Ξ, a non-dimensional quantity proportional to the applied voltage. Stable and unstable regions of Λ−βo−Ξ space were distinguished. Results indicate a strong stabilizing effect for higher values of β0. The experimental study, using silicone and ricinus oil to approximate zero gravity conditions fully confirmed quantitatively the theoretical results.
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Rochlin, M. W., and H. B. Peng. "Localization of intracellular proteins at acetylcholine receptor clusters induced by electric fields in Xenopus muscle cells." Journal of Cell Science 94, no. 1 (September 1, 1989): 73–83. http://dx.doi.org/10.1242/jcs.94.1.73.
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Electric fields cause acetylcholine receptor (AChR) patches to form on the cathodal sides of cultured muscle cells. These patches are stable for several hours following cessation of an electric field treatment, indicating that the receptors are anchored to the cluster sites. Furthermore, at the ultrastructural level, AChR patches induced by electric fields are marked by an accumulation of extracellular matrix material and a sarcolemmal density. Thus, these AChR patches are similar to those induced by other stimuli, including nerve, polycation-coated beads, and the tissue culture substratum. Proteins that may be involved in anchoring AChRs have been colocalized with AChR patches induced by the latter three stimuli, but not at AChR patches induced by electric fields. In this study, we demonstrate that three putative anchoring proteins, 43K (K = 10(3) Mr) protein, 58K protein and talin, are associated with field-induced AChR patches. We also show that these proteins persist at field-induced AChR patches following removal of the field, indicating that they are stabilized at the AChR patch. Our data are consistent with the possibility that these proteins contribute to the stabilization of AChRs at patches induced by the electric field. Since 43K, 58K and talin are intracellular proteins, and therefore could not undergo field-induced lateral electrophoresis, our observations support the notion that the electric field triggers the formation of an AChR-stabilizing specialization.
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Ponce-Torres, A., N. Rebollo-Muñoz, M. A. Herrada, A. M. Gañán-Calvo, and J. M. Montanero. "The steady cone-jet mode of electrospraying close to the minimum volume stability limit." Journal of Fluid Mechanics 857 (October 22, 2018): 142–72. http://dx.doi.org/10.1017/jfm.2018.737.
Повний текст джерелаАнотація:
We study both numerically and experimentally the steady cone-jet mode of electrospraying close to the stability limit of minimum flow rate. The leaky dielectric model is solved for arbitrary values of the relative permittivity and the electrohydrodynamic Reynolds number. The linear stability analysis of the base flows is conducted by calculating their global eigenmodes. The minimum flow rate is determined as that for which the growth factor of the dominant mode becomes positive. We find a good agreement between this theoretical prediction and experimental values. The analysis of the spatial structure of the dominant perturbation may suggest that instability originates in the cone-jet transition region, which shows the local character of the cone-jet mode. The electric relaxation time is considerably smaller than the residence time of a fluid particle in the cone-jet transition region (defined as the region where the surface and bulk intensities are of the same order of magnitude) except for the high-polarity case, where these characteristic times are commensurate with each other. The superficial charge is not relaxed within the cone-jet transition region except for the high-viscosity case, because significant inner electric fields arise in the cone-jet transition region. However, those electric fields are not large enough to invalidate the scaling laws that do not take them into account. Viscosity and polarization forces compete against the driving electric shear stress in the cone-jet transition region for small Reynolds numbers and large relative permittivities, respectively. Capillary forces may also play a significant role in the minimum flow rate stability limit. The experiments show the noticeable stabilizing effect of the feeding capillary for diameters even two orders of magnitude larger than that of the jet. Stable jets with electrification levels higher than the Rayleigh limit are produced. During the jet break-up, two consecutive liquid blobs may coalesce and form a bigger emitted droplet, probably due to the jet acceleration. The size of droplets exceeds Rayleigh’s prediction owing to the stabilizing effect of both the axial electric field and viscosity.
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Rudolph, P., and K. Kakimoto. "Crystal Growth from the Melt under External Force Fields." MRS Bulletin 34, no. 4 (April 2009): 251–58. http://dx.doi.org/10.1557/mrs2009.75.
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AbstractThe present and future demands of industrial bulk crystal growth from the melt are concentrated on improved crystal quality, increased yield, and reduced costs. To meet these challenges, the size of the melt volume must be markedly increased. As a result, violent convective perturbations appear within the melts due to turbulent heat and mass flows. They disturb the single crystal growth and give rise to compositional inhomogeneities. The application of external force fields is an effective method to dampen and control these flows. After introducing different stabilizing variants, such as constant and accelerated melt rotation, mechanical vibrations, and electric current, this article focuses on the use of magnetic fields. Nonsteady fields became very popular because, in this case, the needed strength of the magnetic induction is much lower than for steady fields. A new low-energy low-cost technology that combines heat and magnetic field generation in one module placed close to the melt crucible is introduced.
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Chen, Zheng, Hong Li, Adil Yolbarsop, Yuan Zhang, Wentan Yan, Xianhao Rao, Zhen Tao, et al. "Measurement of helicity flux density using the eddy-current diagnostic system in Keda Torus eXperiment device." Physics of Plasmas 29, no. 4 (April 2022): 042108. http://dx.doi.org/10.1063/5.0073486.
Повний текст джерелаАнотація:
The flux of magnetic helicity characterizes how the topology of a magnetic field changes and helicity and its transport play essential roles in plasma equilibrium and instabilities in the reversed-field pinch (RFP) device configuration. Used to suppress magnetohydrodynamic instabilities effectively, the stabilizing conducting shell located at the boundary of an RFP device is always characterized by an eddy-current distribution that evolves rapidly with time. After measuring and analyzing the eddy currents on this stabilizing shell during tokamak discharges in the Keda Torus eXperiment device, the distributions of multiple physical quantities on the shell are obtained, including the magnetic fields, eddy currents, and electric fields. An experimental technique for measuring helicity flux density is demonstrated, combined with eddy-current diagnosis and these physical vectors on the boundary. How the magnetic and current helicity flux densities evolve is given by a feasible mathematical analysis, and data suggest that the plasma mediates both the generation and transport of magnetic helicity during the discharge. The experimental results of the distribution of the magnetic helicity flux densities (MHFDs) due to the instability on the boundary are given, and the average of these MHFDs over the whole boundary surface is far less than the maximum value of the MHFDs. In addition, the results of current helicity flux densities on the boundary are also presented.
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Welborn, V. Vaissier. "Beyond structural analysis of molecular enzyme-inhibitor interactions." Electronic Structure 4, no. 1 (February 14, 2022): 014006. http://dx.doi.org/10.1088/2516-1075/ac509f.
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Abstract Fast and effective drug discovery processes rely on rational drug design to circumvent the tedious and expensive trial and error approach. However, accurate predictions of new remedies, which are often enzyme inhibitors, require a clear understanding of the nature and function of the key players governing the interaction between the drug candidate and its target. Here, we propose to calculate electric fields to explicitly link structure to function in molecular dynamics simulations, a method that can easily be integrated within the rational drug discovery workflow. By projecting the electric fields onto specific bonds, we can identify the system components that are at the origin of stabilizing intermolecular interactions (covalent and non-covalent) in the active site. This helps to significantly narrow the exploration space when predicting new inhibitors. To illustrate this method, we characterize the binding of the non-covalent inhibitor X77 to the main protease of SARS-CoV-2, a particularly time-sensitive drug discovery problem. With electric field calculations, we were able to identify three key residues (Asn-142, Met-165 and Glu-166), that have functional consequences on X77. This contrasts with the nearly 20 residues reported in previous studies as being in close contact with inhibitors in the active site of the protease. As a result, the search for new non-covalent inhibitors can now be accelerated by techniques that look to optimize the interaction between candidate molecules and these residues.
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Oks, Eugene. "Review of Classical Analytical Results for the Motion of a Rydberg Electron around a Polar Molecule under Magnetic or Electric Fields of Arbitrary Strengths in Axially Symmetric Configurations." Symmetry 13, no. 11 (November 12, 2021): 2171. http://dx.doi.org/10.3390/sym13112171.
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We review classical studies of the oscillatory-precessional motion of an electron in the field of an electric dipole (the latter representing the polar molecule) with or without external magnetic or electric fields. The focus is on the most recent studies. In one study (at zero external field), it was shown that, generally, the oscillations being in the meridional direction and the precession being along parallels of latitude can take place on the same time scale—contrary to the statement from the previous literature. In another study, it was shown that a magnetic field enables new ranges of the bound oscillatory-precessional motion of the Rydberg electron and that in one of the new ranges, the period of the θ-oscillations has the non-monotonic dependence on primary parameter of the system. This is a counterintuitive result. In yet another study, it was shown that under the electric field there are two equilibrium circular states of a positive energy and one equilibrium state of a negative energy. The existence of the equilibrium state of the negative energy is a counterintuitive result since at the absence of the field, the bound state was possible only for the zero energy. Thus, it is a counterintuitive result that in this case the electric field can play the role of a stabilizing factor.
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Mitra-Delmotte, Gargi, and Asoke Nath Mitra. "Softening the “Crystal Scaffold” for Life’s Emergence." Physics Research International 2012 (February 21, 2012): 1–13. http://dx.doi.org/10.1155/2012/232864.
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Del Giudice’s group studies how water can organize on hydrophilic surfaces forming coherent domains (loaning energy from the quantum vacuum), plus quasifree electrons, whose excitations produce cold vortices, aligning to ambient fields. Their electric and magnetic dipolar modes can couple to oscillatory (electric-organic dipoles) and/or rotary (magnetic-mineral dipoles), besides responding to magnetic potentials. Thus, imprinted electromagnetic patterns of catalytic colloids—compared with Cairns-Smith’s “crystal scaffold”—on their structured water partners could have equipped the latter with a selection basis for “choosing” their context-based “soft-matter” (de Gennes) replacements. We consider the potential of the scenario of an external control on magnetic colloids forming in the Hadean hydrothermal setting (of Russell and coworkers)—via a magnetic rock field—conceptually enabling self-assembly, induction of asymmetries, response effects towards close-to-equilibrium dynamics, and associative networks, besides providing a coherent environment for stabilizing associated symmetry-broken quanta and their feedback interactions with those of coherent water domains, to address the emergence of metabolism and replication.
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Vitkova, Victoria, Vesela Yordanova, Galya Staneva, Ognyan Petkov, Angelina Stoyanova-Ivanova, Krassimira Antonova, and Georgi Popkirov. "Dielectric Properties of Phosphatidylcholine Membranes and the Effect of Sugars." Membranes 11, no. 11 (October 30, 2021): 847. http://dx.doi.org/10.3390/membranes11110847.
Повний текст джерелаАнотація:
Simple carbohydrates are associated with the enhanced risk of cardiovascular disease and adverse changes in lipoproteins in the organism. Conversely, sugars are known to exert a stabilizing effect on biological membranes, and this effect is widely exploited in medicine and industry for cryopreservation of tissues and materials. In view of elucidating molecular mechanisms involved in the interaction of mono- and disaccharides with biomimetic lipid systems, we study the alteration of dielectric properties, the degree of hydration, and the rotational order parameter and dipole potential of lipid bilayers in the presence of sugars. Frequency-dependent deformation of cell-size unilamellar lipid vesicles in alternating electric fields and fast Fourier transform electrochemical impedance spectroscopy are applied to measure the specific capacitance of phosphatidylcholine lipid bilayers in sucrose, glucose and fructose aqueous solutions. Alteration of membrane specific capacitance is reported in sucrose solutions, while preservation of membrane dielectric properties is established in the presence of glucose and fructose. We address the effect of sugars on the hydration and the rotational order parameter for 1-palmitoyl-2-oleoyl-sn-glycero-3- phosphocholine (POPC) and 1-stearoyl-2-oleoyl-sn-glycero-3- phosphocholine (SOPC). An increased degree of lipid packing is reported in sucrose solutions. The obtained results provide evidence that some small carbohydrates are able to change membrane dielectric properties, structure, and order related to membrane homeostasis. The reported data are also relevant to future developments based on the response of lipid bilayers to external physical stimuli such as electric fields and temperature changes.
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Tai, Jung-Shen B., Paul J. Ackerman, and Ivan I. Smalyukh. "Topological transformations of Hopf solitons in chiral ferromagnets and liquid crystals." Proceedings of the National Academy of Sciences 115, no. 5 (January 17, 2018): 921–26. http://dx.doi.org/10.1073/pnas.1716887115.
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Liquid crystals are widely known for their facile responses to external fields, which forms a basis of the modern information display technology. However, switching of molecular alignment field configurations typically involves topologically trivial structures, although singular line and point defects often appear as short-lived transient states. Here, we demonstrate electric and magnetic switching of nonsingular solitonic structures in chiral nematic and ferromagnetic liquid crystals. These topological soliton structures are characterized by Hopf indices, integers corresponding to the numbers of times that closed-loop-like spatial regions (dubbed “preimages”) of two different single orientations of rod-like molecules or magnetization are linked with each other. We show that both dielectric and ferromagnetic response of the studied material systems allow for stabilizing a host of topological solitons with different Hopf indices. The field transformations during such switching are continuous when Hopf indices remain unchanged, even when involving transformations of preimages, but discontinuous otherwise.
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Simitev, Radostin D., and Friedrich H. Busse. "Onset of Inertial Magnetoconvection in Rotating Fluid Spheres." Fluids 6, no. 1 (January 13, 2021): 41. http://dx.doi.org/10.3390/fluids6010041.
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The onset of convection in the form of magneto-inertial waves in a rotating fluid sphere permeated by a constant axial electric current is studied in this paper. Thermo-inertial convection is a distinctive flow regime on the border between rotating thermal convection and wave propagation. It occurs in astrophysical and geophysical contexts where self-sustained or external magnetic fields are commonly present. To investigate the onset of motion, a perturbation method is used here with an inviscid balance in the leading order and a buoyancy force acting against weak viscous dissipation in the next order of approximation. Analytical evaluation of constituent integral quantities is enabled by applying a Green’s function method for the exact solution of the heat equation following our earlier non-magnetic analysis. Results for the case of thermally infinitely conducting boundaries and for the case of nearly thermally insulating boundaries are obtained. In both cases, explicit expressions for the dependence of the Rayleigh number on the azimuthal wavenumber are derived in the limit of high thermal diffusivity. It is found that an imposed azimuthal magnetic field exerts a stabilizing influence on the onset of inertial convection and as a consequence magneto-inertial convection with azimuthal wave number of unity is generally preferred.
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Pathak, Sarthak, Alessandro Moro, Hiromitsu Fujii, Atsushi Yamashita, and Hajime Asama. "Spherical Video Stabilization by Estimating Rotation from Dense Optical Flow Fields." Journal of Robotics and Mechatronics 29, no. 3 (June 20, 2017): 566–79. http://dx.doi.org/10.20965/jrm.2017.p0566.
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[abstFig src='/00290003/12.jpg' width='300' text='Spherical video stabilization' ] We propose a method for stabilizing spherical videos by estimating and removing the effect of camera rotation using dense optical flow fields. By derotating each frame in the video to the orientation of its previous frame in two dense approaches, we estimate the complete 3 DoF rotation of the camera and remove it to stabilize the spherical video. Following this, any chosen area on the spherical video (equivalent of a normal camera’s field of view) is unwarped to result in a ‘rotation-less virtual camera’ that can be oriented independent of the camera motion. This can help in perception of the environment and camera motion much better. In order to achieve this, we use dense optical flow, which can provide important information about camera motion in a static environment and can have several advantages over sparse feature-point based approaches. The spatial regularization property of dense optical flow provides more stable motion information as compared to tracking sparse points and negates the effect of feature point outliers. We show superior results as compared to using sparse feature points alone.
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Edelmann, Janis, Andrew J. Petruska, and Bradley J. Nelson. "Magnetic control of continuum devices." International Journal of Robotics Research 36, no. 1 (January 2017): 68–85. http://dx.doi.org/10.1177/0278364916683443.
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In this paper we apply Cosserat rod theory to catheters with permanent magnetic components that are subject to spatially varying magnetic fields. The resulting model formulation captures the magnetically coupled catheter behavior and provides numerical solutions for rod equilibrium configurations in real-time. The model is general, covering cases with different catheter geometries, multiple magnetic components, and various boundary constraints. The necessary Jacobians for quasi-static, closed-loop control using an electromagnetic coil system and a motorized advancer are derived and incorporated into a visual-feedback controller. We address the issue of solution bifurcations caused by the magnetic field by proposing an additional, stabilizing control method that makes use of system redundancies. We demonstrate the effectiveness of the model by performing 3D tip-position trajectories with root-mean-square distance errors of 2.7 mm in open-loop, 0.30 mm in closed-loop, and 0.42 mm in stabilizing closed-loop modes. The stabilizing controller achieved on average a factor of 1.6 increase in the restoring wrenches for the least stable direction.
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Grigore, Lucian Ștefăniță, Anton Soloi, Ovidiu Tiron, and Ciprianiulian Răcuciu. "Fundamentals of Autonomous Robot Classes with a System of Stabilization of the Gripping Mechanism." Advanced Materials Research 646 (January 2013): 164–70. http://dx.doi.org/10.4028/www.scientific.net/amr.646.164.
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The development of a family of autonomous robots with tracked propeller activated by electrical engines and equipped with very precise „human hand-likeˮgripping will allow their use in various fields. The precision is also ensured by the introduction into the driving system, more precisely into the basis of the driving system, of a stabilizing system of the operational platform. Providing a photovoltaic-type power supply will increase the autonomy of the robot. Finally, the installation of a GoPro Be a HERO s outdoor edition professional camera enables the viewing of an extended field and the transmission of the information to the user through Wi_FiBacPac + Remote compatible. There are many remote areas or whose medium is improper to a direct human intervention. That is why the development of such a family of autonomous robots is extremely useful.
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Melo, Aurelio G., Fabio A. A. Andrade, Ihannah P. Guedes, Guilherme F. Carvalho, Alessandro R. L. Zachi, and Milena F. Pinto. "Fuzzy Gain-Scheduling PID for UAV Position and Altitude Controllers." Sensors 22, no. 6 (March 10, 2022): 2173. http://dx.doi.org/10.3390/s22062173.
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Unmanned aerial vehicle (UAV) applications have evolved to a wide range of fields in the last decade. One of the main challenges in autonomous tasks is the UAV stability during maneuvers. Thus, attitude and position control play a crucial role in stabilizing the vehicle in the desired orientation and path. Many control techniques have been developed for this. However, proportional integral derivative (PID) controllers are often used due their structure and efficiency. Despite PID’s good performance, different requirements may be present at different mission stages. The main contribution of this research work is the development of a novel strategy based on a fuzzy-gain scheduling mechanism to adjust the PID controller to stabilize both position and altitude. This control strategy must be effective, simple, and robust to uncertainties and external disturbances. The Robot Operating System (ROS) integrates the proposed system and the flight control unit. The obtained results showed that the proposed approach was successfully applied to the trajectory tracking and revealed a good performance compared to conventional PID and in the presence of noises. In the tests, the position controller was only affected when the altitude error was higher, with an error of 2% lower.
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Purohit, Ayushi, Radheshyam Sharma, R. Shiv Ramakrishnan, Stuti Sharma, Ashish Kumar, Devendra Jain, Himmat S. Kushwaha, and Elina Maharjan. "Biogenic Synthesis of Silver Nanoparticles (AgNPs) Using Aqueous Leaf Extract of Buchanania lanzan Spreng and Evaluation of Their Antifungal Activity against Phytopathogenic Fungi." Bioinorganic Chemistry and Applications 2022 (March 10, 2022): 1–9. http://dx.doi.org/10.1155/2022/6825150.
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Nanoparticles show the multidisciplinary versatile utility and are gaining the prime place in various fields, such as medicine, electronics, pharmaceuticals, electrical designing, cosmetics, food industries, and agriculture, due to their small size and large surface to volume ratio. Biogenic or green synthesis methods are environmentally friendly, economically feasible, rapid, free of organic solvents, and reliable over conventional methods. Plant extracts are of incredible potential in the biosynthesis of metal nanoparticles owing to their bountiful availability, stabilizing, and reducing ability. In the present study, the aqueous leaf extract of Buchanania lanzan Spreng was mixed with 0.5 mM silver nitrate and incubated at 70°C for 1 h and synthesized a good quantity of AgNPs. The synthesized AgNPs were characterized using UV-visible spectroscopy, X-ray diffractometry (XRD), dynamic light scattering (DLS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The maximum absorption of UV-visible spectra was obtained in the range of 420–430 nm. Furthermore, SEM and TEM results inferred that the size of the particles were 23–62 nm, spherical, crystalline, uniformly distributed, and negatively charged with the zeta potential of −27.6 mV. In addition, the antifungal activities of the AgNPs were evaluated against two phytopathogenic fungi Rhizoctonia solani and Fusarium oxysporum f. sp. lycopersici in vitro using poison food techniques on PDA media. The maximum rate of mycelia inhibition was found in 150 ppm concentration of AgNPs against both phytopathogenic fungi.
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Perito, Brunella, Emilia Giorgetti, Paolo Marsili, and Maurizio Muniz-Miranda. "Antibacterial activity of silver nanoparticles obtained by pulsed laser ablation in pure water and in chloride solution." Beilstein Journal of Nanotechnology 7 (March 18, 2016): 465–73. http://dx.doi.org/10.3762/bjnano.7.40.
Повний текст джерелаАнотація:
Silver nanoparticles (AgNPs) have increasingly gained importance as antibacterial agents with applications in several fields due to their strong, broad-range antimicrobial properties. AgNP synthesis by pulsed laser ablation in liquid (PLAL) permits the preparation of stable Ag colloids in pure solvents without capping or stabilizing agents, producing AgNPs more suitable for biomedical applications than those prepared with common, wet chemical preparation techniques. To date, only a few investigations into the antimicrobial effect of AgNPs produced by PLAL have been performed. These have mainly been performed by ablation in water with nanosecond pulse widths. We previously observed a strong surface-enhanced Raman scattering (SERS) signal from such AgNPs by “activating” the NP surface by the addition of a small quantity of LiCl to the colloid. Such surface effects could also influence the antimicrobial activity of the NPs. Their activity, on the other hand, could also be affected by other parameters linked to the ablation conditions, such as the pulse width. The antibacterial activity of AgNPs was evaluated for NPs obtained either by nanosecond (ns) or picosecond (ps) PLAL using a 1064 nm ablation wavelength, in pure water or in LiCl aqueous solution, withEscherichia coliandBacillus subtilisas references for Gram-negative and Gram-positive bacteria, respectively. In all cases, AgNPs with an average diameter less than 10 nm were obtained, which has been shown in previous works to be the most effective size for bactericidal activity. The measured zeta-potential values were very negative, indicating excellent long-term colloidal stability. Antibacterial activity was observed against both microorganisms for the four AgNP formulations, but the ps-ablated nanoparticles were shown to more effectively inhibit the growth of both microorganisms. Moreover, LiCl modified AgNPs were the most effective, showing minimum inhibitory concentration (MIC) values in a restricted range of 1.0–3.7 µg/mL. An explanation is proposed for this result based on the increased surface reactivity of the metal surface due to the presence of positively charged active sites.
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Fischer, Cameron Ivans. "Multi-Point Mapping of Thunderstorm Electrical Structures." Proceedings of the Wisconsin Space Conference 1, no. 1 (February 25, 2022). http://dx.doi.org/10.17307/wsc.v1i1.354.
Повний текст джерелаАнотація:
Electric field measurements are necessary to understand thunderstorm evolution and lightning initiation. However, most existing measurements are made with single instruments carried by weather balloons. It is difficult to interpret such data since a change in observed electric field could be due either to motion of the instrument or charging/discharging currents. In order to decouple these behaviors, it is necessary to make simultaneous measurements at multiple locations. To avoid the complexity of multiple balloon launches, we describe a single balloon instrument with multiple, independent dropsondes to be released at desired time intervals. The dropsondes are designed to rotate and be self-stabilizing, enabling them to measure electric fields as they fall. The dropsondes are lightweight, robust, and low-cost, and include a preamplifier, GPS receiver, search coil and accelerometer for orientation sensing, microcontroller, and a telemetry system to transmit data to a ground station. Prototype instruments have been drop-tested to demonstrate aerodynamic stability and rotation and have been calibrated for electric field measurement. A balloon payload set to release a set of such dropsondes via hot-wire release mechanisms can thus accomplish the goal of multi-point measurements of thunderstorm electrical structures.
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Zhang, Ke, Anatoliy Glushchenko, and John L. West. "Ordered Micro-Particle Structures in a Liquid Crystal: Formation and Physical Properties." MRS Proceedings 817 (2004). http://dx.doi.org/10.1557/proc-817-l6.27.
Повний текст джерелаАнотація:
AbstractOrdered colloids are of great scientific and practical interests. Liquid crystals offer enhanced ways of producing and stabilizing these complex structures. We therefore studied the rheological and electro-rheological properties of the structured colloids as a means of probing this stabilization. We found that the mechanical properties of the colloids and stability of their 3D structures can be controlled by the particles size and distribution. In addition, when an electric field is applied, we observed an increase in the apparent viscosity with saturation at high electric fields. This effect depends on the shear rate and temperature. The results are also compared with the published data for the viscosity measurements of pure liquid crystals and isotropic colloids. While we are only beginning to understand the details of these complex colloids we expect they will find a wide variety of applications.
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Galeski, S., X. Zhao, R. Wawrzyńczak, T. Meng, T. Förster, P. M. Lozano, S. Honnali, et al. "Unconventional Hall response in the quantum limit of HfTe5." Nature Communications 11, no. 1 (November 23, 2020). http://dx.doi.org/10.1038/s41467-020-19773-y.
Повний текст джерелаАнотація:
AbstractInteracting electrons confined to their lowest Landau level in a high magnetic field can form a variety of correlated states, some of which manifest themselves in a Hall effect. Although such states have been predicted to occur in three-dimensional semimetals, a corresponding Hall response has not yet been experimentally observed. Here, we report the observation of an unconventional Hall response in the quantum limit of the bulk semimetal HfTe5, adjacent to the three-dimensional quantum Hall effect of a single electron band at low magnetic fields. The additional plateau-like feature in the Hall conductivity of the lowest Landau level is accompanied by a Shubnikov-de Haas minimum in the longitudinal electrical resistivity and its magnitude relates as 3/5 to the height of the last plateau of the three-dimensional quantum Hall effect. Our findings are consistent with strong electron-electron interactions, stabilizing an unconventional variant of the Hall effect in a three-dimensional material in the quantum limit.
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Thakur, Sneha, Krishna Mohan G., and Sandhya Rani M. "Plant-Mediated Synthesis of Silver Nanoparticles – A Critical Review." International Journal of Pharmacognosy and Phytochemical Research 9, no. 07 (January 1, 2018). http://dx.doi.org/10.25258/phyto.v9i07.11161.
Повний текст джерелаАнотація:
Nanomedicine is a revolutionary science nanoparticles of size 1 - 100nm designed for the utilization in disease diagnostics and therapeutics, targeted drug delivery of drugs which have difficulty in solubility and bioavailability and also to be applied in numerous fields. The present critical review aims at enumerating the advantages, synthesis and characterization methods, as well as diversified applications of green silver nanoparticles. Silver nanoparticles is an attractive proposition due to their distinctive physical, chemical and biological properties including a high electrical as well as thermal conductivity, surface-enhanced Raman scattering, chemical stability, catalytic activity and non linear optical behavior which enables them of potential value in inks, microelectronics, and medical imaging. Plant mediated synthesis of silver nanoparticles (AgNPs) is now-a-day’s gaining enormous interest as it is cost effective, ecofriendly and has less side effects since there is no addition of external stabilizing or capping agents as the plant itself acts as stabilizing or capping agent. The secondary metabolites and other plant products like proteins, metabolites like alkaloids, terpinoids, saponins, glycosides etc are known to act as external stabilizing or capping agents. The plant mediated silver nanoparticles are known to show uniform particles characteristics and morphology. The bottom to top end approach of synthesis is effective to achieve desired particles size, shape and morphology. The synthesized green silver nanoparticles are characterized by UVVis spectroscopy, SEM/TEM analysis, EDAX/EDS, FTIR and other methods zeta potential measurement, thermo gravimetric analysis, Raman scattering. The plant mediated synthesized silver nanoparticles (green silver nanoparticles) are effective in delivering pharmacological activities like antimicrobial, anticancer, larvicidal etc. Also green Silver nanoparticles have diverse applications acting as biosensors, as targeted drug delivery candidates, in diagnostics and therapeutics, in medical and consumer products, as anti pollutant and in agriculture. The future perspective holds promising results in green synthesis of silver nanoparticles involving plants. This review projects a collective sequence of information for synthesizing and evaluation of green silver nanoparticles and scope of its pharmacological actions.