The Experts below are selected from a list of 146202 Experts worldwide ranked by ideXlab platform
Peter R C Gascoyne - One of the best experts on this subject based on the ideXlab platform.
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cell separation on microfabricated electrodes using dielectrophoretic Gravitational Field flow fractionation
1999Co-Authors: Jun Yang, Ying Huang, Xiaobo Wang, And Frederick F Becker, Peter R C GascoyneAbstract:Dielectrophoretic/Gravitational Field-flow fractionation (DEP/G-FFF) was used to separate cultured human breast cancer MDA-435 cells from normal blood cells mixed together in a sucrose/dextrose medium. An array of microfabricated, interdigitated electrodes of 50 μm widths and spacings, and lining the bottom surface of a thin chamber (0.42 mm H × 25 mm W × 300 mm L), was used to generate DEP forces that levitated the cells. A 10-μL cell mixture sample containing ∼50 000 cells was introduced into the chamber, and cancerous and normal blood cells were levitated to different heights according to the balance of DEP and Gravitational forces. The cells at different heights were transported at different velocities under the influence of a parabolic flow profile that was established in the chamber and were thereby separated. Separation performance depended on the frequency and voltage of the applied DEP Field and the fluid-flow rate. It took as little as 5 min to achieve cell separation. An analysis of the DEP/G-F...
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separation of polystyrene microbeads using dielectrophoretic Gravitational Field flow fractionation
1998Co-Authors: Xiaobo Wang, Jody Vykoukal, Frederick F Becker, Peter R C GascoyneAbstract:Abstract The characterization of a dielectrophoretic/Gravitational Field-flow-fractionation (DEP/G-FFF) system using model polystyrene (PS) microbeads is presented. Separations of PS beads of different surface functionalization (COOH and none) and different sizes (6, 10, and 15 μ m in diameter) are demonstrated. To investigate the factors influencing separation performance, particle elution times were determined as a function of particle suspension conductivity, fluid flow rate, and applied Field frequency and voltage. Experimental data were analyzed using a previously reported theoretical model and good agreement between theory and experiment was found. It was shown that separation of PS beads was based on the differences in their effective dielectric properties. Particles possessing different dielectric properties were positioned at different heights in a fluid-flow profile in a thin chamber by the balance of DEP and Gravitational forces, transported at different velocities under the influence of the fluid flow, and thereby separated. To explore hydrodynamic (HD) lift effects, velocities of PS beads were determined as a function of fluid flow rate in the separation chamber when no DEP Field was applied. In this case, particle equilibrium height positions were governed solely by the balance of HD lift and Gravitational forces. It was concluded that under the experimental conditions reported here, the DEP force was the dominant factor in controlling particle equilibrium height and that HD lift force played little role in DEP/G-FFF operation. Finally, the influence of various experimental parameters on separation performance was discussed for the optimization of DEP/G-FFF.
Luigi Rosa - One of the best experts on this subject based on the ideXlab platform.
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energy momentum tensor of a casimir apparatus in a weak Gravitational Field scalar case
2008Co-Authors: Giampiero Esposito, George M Napolitano, Luigi RosaAbstract:Recent work in the literature had evaluated the energy-momentum tensor of a Casimir apparatus in a weak Gravitational Field, for an electromagnetic Field subject to perfect conductor boundary conditions on parallel plates. The Casimir apparatus was then predicted to experience a tiny push in the upward direction, and the regularized energy-momentum tensor was evaluated to first order in the Gravitational acceleration. This analysis made it desirable to assess what happens in a simpler case. For this purpose, the present paper studies a free, real massless scalar Field subject to homogeneous Dirichlet conditions on the parallel plates. Working again to first order in the constant gravity acceleration, the resulting regularized and renormalized energy-momentum tensor is found to be covariantly conserved, while the trace anomaly vanishes if the massless scalar Field is conformally coupled to gravity. Conformal coupling also ensures a finite Casimir energy and finite values of the pressure upon parallel plates. (Less)
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relativistic mechanics of casimir apparatuses in a weak Gravitational Field
2007Co-Authors: Giuseppe Bimonte, E Calloni, Giampiero Esposito, Luigi RosaAbstract:This paper derives a set of general relativistic cardinal equations for the equilibrium of an extended body in a uniform Gravitational Field. These equations are essential for a proper understanding of the mechanics of suspended relativistic systems. As an example, the prototypical case of a suspended vessel filled with radiation is discussed. The mechanics of Casimir apparatuses at rest in the Gravitational Field of the Earth is then considered. Starting from an expression for the Casimir energy-momentum tensor in a weak Gravitational Field recently derived by the authors, it is shown here that, in the case of a rigid cavity supported by a stiff mount, the weight of the Casimir energy E c stored in the cavity corresponds to a Gravitational mass M = E c /c 2 , in agreement with the covariant conservation law of the regularized energy-momentum tensor. The case of a cavity consisting of two disconnected plates supported by separate mounts, where the two measured forces cannot be obtained by straightforward arguments, is also discussed.
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energy momentum tensor for a casimir apparatus in a weak Gravitational Field
2006Co-Authors: Giuseppe Bimonte, E Calloni, Giampiero Esposito, Luigi RosaAbstract:The influence of the gravity acceleration on the regularized energy-momentum tensor of the quantized electromagnetic Field between two plane-parallel conducting plates is derived. We use Fermi coordinates and work to first order in the constant acceleration parameter. A perturbative expansion, to this order, of the Green functions involved and of the energy-momentum tensor is derived by means of the covariant geodesic point-splitting procedure. In correspondence to the Green functions satisfying mixed and gauge-invariant boundary conditions, and Ward identities, the energy-momentum tensor is covariantly conserved and satisfies the expected relation between gauge-breaking and ghost parts, while a new simple formula for the trace anomaly is obtained to first order in the constant acceleration. A more systematic derivation is therefore obtained of the theoretical prediction according to which the Casimir device in a weak Gravitational Field will experience a tiny push in the upwards direction.
Alexander J Silenko - One of the best experts on this subject based on the ideXlab platform.
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quasi uniform Gravitational Field of a disk revisited
2019Co-Authors: Alexander J Silenko, Yury A TsalkouAbstract:We calculate the quasi-uniform Gravitational Field of a disk in the weak-Field approximation and demonstrate an inappropriateness of preceding results. The Riemann tensor of this Field is determine...
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quasi uniform Gravitational Field of a disk revisited
2018Co-Authors: Alexander J Silenko, Yury A TsalkouAbstract:We calculate the quasi-uniform Gravitational Field of a disk in the weak-Field approximation and demonstrate an inappropriateness of preceding results. The Riemann tensor of this Field is determined. The nonexistence of the uniform Gravitational Field is proven without the use of the weak-Field approximation. The previously found difference between equations of motion for the momentum and spin in the accelerated frame and in the quasi-uniform Gravitational Field also takes place for the disk. However, it does not violate the Einstein equivalence principle because of the nonexistence of the uniform Gravitational Field.
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spin in an arbitrary Gravitational Field
2013Co-Authors: Yuri N Obukhov, Alexander J Silenko, O V TeryaevAbstract:We study the quantum mechanics of a Dirac fermion on a curved spacetime manifold. The metric of the spacetime is completely arbitrary, allowing for the discussion of all possible inertial and Gravitational Field configurations. In this framework, we find the Hermitian Dirac Hamiltonian for an arbitrary classical external Field (including the Gravitational and electromagnetic ones). In order to discuss the physical content of the quantum-mechanical model, we further apply the Foldy-Wouthuysen transformation, and derive the quantum equations of motion for the spin and position operators. We analyze the semiclassical limit of these equations and compare the results with the dynamics of a classical particle with spin in the framework of the standard Mathisson-Papapetrou theory and in the classical canonical theory. The comparison of the quantum-mechanical and classical equations of motion of a spinning particle in an arbitrary Gravitational Field shows their complete agreement.
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semiclassical limit for dirac particles interacting with a Gravitational Field
2005Co-Authors: Alexander J Silenko, O V TeryaevAbstract:The behavior of a spin-1/2 particle in a weak static Gravitational Field is considered. The Dirac Hamiltonian is diagonalized by the Foldy-Wouthuysen transformation providing also the simple form for the momentum and spin polarization operators. The operator equations of momentum and spin motion are derived for a first time. Their semiclassical limit is analyzed. The dipole spin-gravity coupling in the previously found (another) Hamiltonian does not lead to any observable effects. The general agreement between the quantum and classical approaches is established, contrary to several recent claims. The expression for the Gravitational Stern-Gerlach force is derived. The helicity evolution in the Gravitational Field and corresponding accelerated frame coincides, being the manifestation of the equivalence principle.
Xiaobo Wang - One of the best experts on this subject based on the ideXlab platform.
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cell separation on microfabricated electrodes using dielectrophoretic Gravitational Field flow fractionation
1999Co-Authors: Jun Yang, Ying Huang, Xiaobo Wang, And Frederick F Becker, Peter R C GascoyneAbstract:Dielectrophoretic/Gravitational Field-flow fractionation (DEP/G-FFF) was used to separate cultured human breast cancer MDA-435 cells from normal blood cells mixed together in a sucrose/dextrose medium. An array of microfabricated, interdigitated electrodes of 50 μm widths and spacings, and lining the bottom surface of a thin chamber (0.42 mm H × 25 mm W × 300 mm L), was used to generate DEP forces that levitated the cells. A 10-μL cell mixture sample containing ∼50 000 cells was introduced into the chamber, and cancerous and normal blood cells were levitated to different heights according to the balance of DEP and Gravitational forces. The cells at different heights were transported at different velocities under the influence of a parabolic flow profile that was established in the chamber and were thereby separated. Separation performance depended on the frequency and voltage of the applied DEP Field and the fluid-flow rate. It took as little as 5 min to achieve cell separation. An analysis of the DEP/G-F...
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separation of polystyrene microbeads using dielectrophoretic Gravitational Field flow fractionation
1998Co-Authors: Xiaobo Wang, Jody Vykoukal, Frederick F Becker, Peter R C GascoyneAbstract:Abstract The characterization of a dielectrophoretic/Gravitational Field-flow-fractionation (DEP/G-FFF) system using model polystyrene (PS) microbeads is presented. Separations of PS beads of different surface functionalization (COOH and none) and different sizes (6, 10, and 15 μ m in diameter) are demonstrated. To investigate the factors influencing separation performance, particle elution times were determined as a function of particle suspension conductivity, fluid flow rate, and applied Field frequency and voltage. Experimental data were analyzed using a previously reported theoretical model and good agreement between theory and experiment was found. It was shown that separation of PS beads was based on the differences in their effective dielectric properties. Particles possessing different dielectric properties were positioned at different heights in a fluid-flow profile in a thin chamber by the balance of DEP and Gravitational forces, transported at different velocities under the influence of the fluid flow, and thereby separated. To explore hydrodynamic (HD) lift effects, velocities of PS beads were determined as a function of fluid flow rate in the separation chamber when no DEP Field was applied. In this case, particle equilibrium height positions were governed solely by the balance of HD lift and Gravitational forces. It was concluded that under the experimental conditions reported here, the DEP force was the dominant factor in controlling particle equilibrium height and that HD lift force played little role in DEP/G-FFF operation. Finally, the influence of various experimental parameters on separation performance was discussed for the optimization of DEP/G-FFF.
Hendrik Ulbricht - One of the best experts on this subject based on the ideXlab platform.
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Testing the Gravitational Field generated by a quantum superposition
2019Co-Authors: Matteo Carlesso, Angelo Bassi, Mauro Paternostro, Hendrik UlbrichtAbstract:What Gravitational Field is generated by a massive quantum system in a spatial superposition? Despite decades of intensive theoretical and experimental research, we still do not know the answer. On the experimental side, the difficulty lies in the fact that gravity is weak and requires large masses to be detectable. However, it becomes increasingly difficult to generate spatial quantum superpositions for increasingly large masses, in light of the stronger environmental effects on such systems. Clearly, a delicate balance between the need for strong Gravitational effects and weak decoherence should be found. We show that such a trade off could be achieved in an optomechanics scenario that allows to determine whether the Gravitational Field generated by a quantum system in a spatial superposition is in a coherent superposition or not. We estimate the magnitude of the effect and show that it offers perspectives for observability.
