Comment on Repulsive Casimir Forces
Iannuzzi, D
2003-01-01
A recent theoretical calculation shows that the Casimir force between two parallel plates can be repulsive for plates with nontrivial magnetic properties (O. Kenneth et al., Phys. Rev. Lett. 89, 033001 (2002)). According to the authors, the effect may be observed with known materials, such as ferrites and garnets, and it might be possible to engineer micro- or nanoelectromechanical systems (MEMS or NEMS) that could take advantage of a short range repulsive force. Here we show that on the contrary the Casimir force between two parallel plates in vacuum at micron and submicron distance is always attractive.
Archimedes Force on Casimir Apparatus
Shevchenko, Vladimir
2016-01-01
We address a problem of Casimir apparatus in dense medium and weak gravitational field. The falling of the apparatus has to be governed by the equivalence principle, with proper account for contributions to the weight of the apparatus from its material part and from distorted quantum fields. We discuss general expression for the corresponding force in metric with cylindrical symmetry. By way of example we compute explicit expression for Archimedes force, acting on the Casimir apparatus of finite size, immersed into thermal bath of free scalar field. It is shown that besides universal term, proportional to the volume of the apparatus, there are non-universal quantum corrections, depending on the boundary conditions.
Nonadditivity of critical Casimir forces
Paladugu, Sathyanarayana; Callegari, Agnese; Tuna, Yazgan; Barth, Lukas; Dietrich, Siegfried; Gambassi, Andrea; Volpe, Giovanni
2016-04-01
In soft condensed matter physics, effective interactions often emerge due to the spatial confinement of fluctuating fields. For instance, microscopic particles dissolved in a binary liquid mixture are subject to critical Casimir forces whenever their surfaces confine the thermal fluctuations of the order parameter of the solvent close to its critical demixing point. These forces are theoretically predicted to be nonadditive on the scale set by the bulk correlation length of the fluctuations. Here we provide direct experimental evidence of this fact by reporting the measurement of the associated many-body forces. We consider three colloidal particles in optical traps and observe that the critical Casimir force exerted on one of them by the other two differs from the sum of the forces they exert separately. This three-body effect depends sensitively on the distance from the critical point and on the chemical functionalisation of the colloid surfaces.
Archimedes force on Casimir apparatus
Shevchenko, Vladimir; Shevrin, Efim
2016-08-01
This paper addresses a problem of Casimir apparatus in dense medium, put in weak gravitational field. The falling of the apparatus has to be governed by the equivalence principle with proper account for contributions to the weight of the apparatus from its material part and from distorted quantum fields. We discuss general expression for the corresponding force in metric with cylindrical symmetry. By way of example, we compute explicit expression for Archimedes force, acting on the Casimir apparatus of finite size, immersed into thermal bath of free scalar field. It is shown that besides universal term, proportional to the volume of the apparatus, there are non-universal quantum corrections, depending on the boundary conditions.
Controlling Casimir force via coherent driving field
Ahmad, Rashid; Abbas, Muqaddar; Ahmad, Iftikhar; Qamar, Sajid
2016-04-01
A four level atom-field configuration is used to investigate the coherent control of Casimir force between two identical plates made up of chiral atomic media and separated by vacuum of width d. The electromagnetic chirality-induced negative refraction is obtained via atomic coherence. The behavior of Casimir force is investigated using Casimir-Lifshitz formula. It is noticed that Casimir force can be switched from repulsive to attractive and vice versa via coherent control of the driving field. This switching feature provides new possibilities of using the repulsive Casimir force in the development of new emerging technologies, such as, micro-electro-mechanical and nano-electro-mechanical systems, i.e., MEMS and NEMS, respectively.
Repulsive Casimir Force using metamaterials
Pappakrishnan, Venkatesh K.; Mundru, Pattabhiraju C.; Genov, Dentcho A.
We investigate conditions for Casimir Force (CF) reversal between two parallel half-space metamaterial plates separated by air or vacuum at ambient temperatures. Practically, the Casimir effect can lead to stiction in nanoscale devices, degradation and decreased performance. While material realizations of repulsive CF has been proposed for high dielectric host materials, so far the CF reversal with air/vacuum as intermediate medium remain challenging. Here, we propose a two plate design based on artificial electromagnetic materials known as metamaterials. This configuration allows a simple analytical treatment that accurately describes the large and short distance asymptotics of CF and allows extraction of important parameters such as lower and upper cutoff gap distances that define the repulsive force window. A parametric study has been performed in terms of the plate's dielectric and magnetic plasma frequencies, plate separation distance and temperature. The parametric domain for achieving CF reversal is identified. If successfully implemented the proposed design could potentially result in frictionless bio-fluid transport devices, quantum levitation and coating for ultra-clean room environment.
Coupled surface polaritons and the Casimir force
Henkel, C; Mulet, J P; Greffet, J J; Henkel, Carsten; Joulain, Karl; Mulet, Jean-Philippe; Greffet, Jean-Jacques
2004-01-01
The Casimir force between metallic plates made of realistic materials is evaluated for distances in the nanometer range. A spectrum over real frequencies is introduced and shows narrow peaks due to surface resonances (plasmon polaritons or phonon polaritons) that are coupled across the vacuum gap. We demonstrate that the Casimir force originates from the attraction (repulsion) due to the corresponding symmetric (antisymmetric) eigenmodes, respectively. This picture is used to derive a simple analytical estimate of the Casimir force at short distances. We recover the result known for Drude metals without absorption and compute the correction for weakly absorbing materials.
Casimir Force Between Quantum Plasmas
International Nuclear Information System (INIS)
Field fluctuations are responsible for an attractive force - the Casimir force - between two parallel (globally neutral) metallic plates separated by a distance d. At high temperature, or equivalently large d, this force is known to exhibit a classical and universal character (independent of the material constitution of the plates). In a recent work, we have displayed the microscopic mechanisms responsible for this universality within a classical model. The plates consist of slabs containing classical charged particles in fluid phase and thermal equilibrium (plasmas). The universality of the force proves to originate from screening sum rules satisfied by the charge correlations. Here we show how this result is altered when the quantum-mechanical nature of the particles is taken into account. It turns out that in addition to the classical result, the asymptotic force for large d comprises a non-universal quantum correction, which is, however, small at high temperature. The method relies on an exact representation of the charge correlations by quantum Mayer graphs, based on the Feynman-Kac path integral formalism. (author)
Stability of suspended graphene under Casimir force
Chudnovsky, E. M.; Zarzuela, R.
2016-08-01
We consider a graphene sheet suspended above a conducting surface. Treating graphene as an elastic membrane subjected to Casimir force, we study its stability against sagging towards the conductor. There exists a critical elevation at the edges below which the central part of the suspended graphene nucleates a trunk that sinks under the action of the Casimir force. The dependence of the critical elevation on temperature, dimensions, and the elastic stress applied to the graphene sheet is computed.
Casimir Forces between Nanoparticles and Substrates
Román-Velázquez, C E; Villarreal, C; Esquivel-Sirvent, R; Noguez, Cecilia
2002-01-01
We study the Casimir force between a nanoparticle and a substrate. We consider the interaction of metal nanoparticles with different substrates within the dipolar approximation. We study the force as a function of the distance for gold and potassium spheres, which are over a substrate of titanium dioxide, sapphire and a perfect conductor. We show that Casimir force is important in systems at the nanometer scale. We study the force as a function of the material properties, radii of the spheres, and the distance between the sphere and the substrate.
Casimir forces beyond the proximity approximation
Bimonte, G; Jaffe, R L; Kardar, M
2011-01-01
The proximity force approximation (PFA) relates the interaction between closely spaced, smoothly curved objects to the force between parallel plates. Precision experiments on Casimir forces necessitate, and spur research on, corrections to the PFA. We use a derivative expansion for gently curved surfaces to derive the leading curvature modifications to the PFA. Our methods apply to any homogeneous and isotropic materials; here we present results for Dirichlet and Neumann boundary conditions and for perfect conductors. A Pad\\'e extrapolation constrained by a multipole expansion at large distance and our improved expansion at short distances, provides an accurate expression for the sphere-plate Casimir force at all separations.
Scattering Theory Approach to Electrodynamic Casimir Forces
Rahi, Sahand Jamal; Graham, Noah; Jaffe, Robert L; Kardar, Mehran
2009-01-01
We give a comprehensive presentation of methods for calculating the Casimir force to arbitrary accuracy, for any number of objects, arbitrary shapes, susceptibility functions, and separations. The technique is applicable to objects immersed in media other than vacuum, nonzero temperatures, and spatial arrangements in which one object is enclosed in another. Our method combines each object's classical electromagnetic scattering amplitude with universal translation matrices, which convert between the bases used to calculate scattering for each object, but are otherwise independent of the details of the individual objects. The method is illustrated by re-deriving the Lifshitz formula for infinite half spaces, by demonstrating the Casimir-Polder to van der Waals cross-over, and by computing the Casimir interaction energy of two infinite, parallel, perfect metal cylinders either inside or outside one another. Furthermore, it is used to obtain new results, namely the Casimir energies of a sphere or a cylinder oppos...
Casimir force measurements from silicon carbide surfaces
Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.
2016-01-01
Using an atomic force microscope we performed measurements of the Casimir force between a gold-coated (Au) microsphere and doped silicon carbide (SiC) samples. The last of these is a promising material for devices operating under severe environments. The roughness of the interacting surfaces was mea
Observation of the thermal Casimir force
Sushkov, A O; Dalvit, D A R; Lamoreaux, S K
2010-01-01
Quantum theory predicts the existence of the Casimir force between macroscopic bodies, due to the zero-point energy of electromagnetic field modes around them. This quantum fluctuation-induced force has been experimentally observed for metallic and semiconducting bodies, although the measurements to date have been unable to clearly settle the question of the correct low-frequency form of the dielectric constant dispersion (the Drude model or the plasma model) to be used for calculating the Casimir forces. At finite temperature a thermal Casimir force, due to thermal, rather than quantum, fluctuations of the electromagnetic field, has been theoretically predicted long ago. Here we report the experimental observation of the thermal Casimir force between two gold plates. We measured the attractive force between a flat and a spherical plate for separations between 0.7 $\\mu$m and 7 $\\mu$m. An electrostatic force caused by potential patches on the plates' surfaces is included in the analysis. The experimental resul...
Probing the Casimir force with optical tweezers
Ether, D S; Umrath, S; Martinez, D; Ayala, Y; Pontes, B; Araújo, G R de S; Frases, S; Ingold, G -L; Rosa, F S S; Viana, N B; Nussenzveig, H M; Neto, P A Maia
2015-01-01
We propose to use optical tweezers to probe the Casimir interaction between microspheres inside a liquid medium for geometric aspect ratios far beyond the validity of the widely employed proximity force approximation. This setup has the potential for revealing unprecedented features associated to the non-trivial role of the spherical curvatures. For a proof of concept, we measure femtonewton double layer forces between polystyrene microspheres at distances above $400$ nm by employing very soft optical tweezers, with stiffness of the order of fractions of a fN/nm. As a future application, we propose to tune the Casimir interaction between a metallic and a polystyrene microsphere in saline solution from attraction to repulsion by varying the salt concentration. With those materials, the screened Casimir interaction may have a larger magnitude than the unscreened one. This line of investigation has the potential for bringing together different fields including classical and quantum optics, statistical physics an...
Matter-screened Casimir force and Casimir-Polder force in planar structures
Raabe, C; Raabe, Christian; Welsch, Dirk-Gunnar
2005-01-01
Using a recently developed theory of the Casimir force (Raabe C and Welsch D-G 2005 Phys. Rev. A 71 013814), we calculate the force that acts on a plate in front of a planar wall and the force that acts on the plate in the case where the plate is part of matter that fills the space in front of the wall. We show that in the limit of a dielectric plate whose permittivity is close to unity, the force obtained in the former case reduces to the ordinary, i.e., unscreened Casimir-Polder force acting on isolated atoms. In the latter case, the theory yields the Casimir-Polder force that is screened by the surrounding matter.
Casimir force measurements from silicon carbide surfaces
Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.
2016-02-01
Using an atomic force microscope we performed measurements of the Casimir force between a gold- coated (Au) microsphere and doped silicon carbide (SiC) samples. The last of these is a promising material for devices operating under severe environments. The roughness of the interacting surfaces was measured to obtain information for the minimum separation distance upon contact. Ellipsometry data for both systems were used to extract optical properties needed for the calculation of the Casimir force via the Lifshitz theory and for comparison to the experiment. Special attention is devoted to the separation of the electrostatic contribution to the measured total force. Our measurements demonstrate large contact potential V0(≈0.67 V ) , and a relatively small density of charges trapped in SiC. Knowledge of both Casimir and electrostatic forces between interacting materials is not only important from the fundamental point of view, but also for device applications involving actuating components at separations of less than 200 nm where surface forces play dominant role.
Critical Casimir forces for colloidal assembly
Nguyen, V. D.; Dang, M. T.; Nguyen, T. A.; Schall, P.
2016-02-01
Critical Casimir forces attract increasing interest due to their opportunities for reversible particle assembly in soft matter and nano science. These forces provide a thermodynamic analogue of the celebrated quantum mechanical Casimir force that arises from the confinement of vacuum fluctuations of the electromagnetic field. In its thermodynamic analogue, solvent fluctuations, confined between suspended particles, give rise to an attractive or repulsive force between the particles. Due to its unique temperature dependence, this effect allows in situ control of reversible assembly. Both the force magnitude and range vary with the solvent correlation length in a universal manner, adjusting with temperature from fractions of the thermal energy, k B T, and nanometre range to several ten kT and micrometer length scale. Combined with recent breakthroughs in the synthesis of complex particles, critical Casimir forces promise the design and assembly of complex colloidal structures, for fundamental studies of equilibrium and out-of-equilibrium phase behaviour. This review highlights recent developments in this evolving field, with special emphasis on the dynamic interaction control to assemble colloidal structures, in and out of equilibrium.
Critical Casimir forces for colloidal assembly
International Nuclear Information System (INIS)
Critical Casimir forces attract increasing interest due to their opportunities for reversible particle assembly in soft matter and nano science. These forces provide a thermodynamic analogue of the celebrated quantum mechanical Casimir force that arises from the confinement of vacuum fluctuations of the electromagnetic field. In its thermodynamic analogue, solvent fluctuations, confined between suspended particles, give rise to an attractive or repulsive force between the particles. Due to its unique temperature dependence, this effect allows in situ control of reversible assembly. Both the force magnitude and range vary with the solvent correlation length in a universal manner, adjusting with temperature from fractions of the thermal energy, k B T, and nanometre range to several ten kT and micrometer length scale. Combined with recent breakthroughs in the synthesis of complex particles, critical Casimir forces promise the design and assembly of complex colloidal structures, for fundamental studies of equilibrium and out-of-equilibrium phase behaviour. This review highlights recent developments in this evolving field, with special emphasis on the dynamic interaction control to assemble colloidal structures, in and out of equilibrium. (topical review)
Critical Casimir forces for colloidal assembly.
Nguyen, V D; Dang, M T; Nguyen, T A; Schall, P
2016-02-01
Critical Casimir forces attract increasing interest due to their opportunities for reversible particle assembly in soft matter and nano science. These forces provide a thermodynamic analogue of the celebrated quantum mechanical Casimir force that arises from the confinement of vacuum fluctuations of the electromagnetic field. In its thermodynamic analogue, solvent fluctuations, confined between suspended particles, give rise to an attractive or repulsive force between the particles. Due to its unique temperature dependence, this effect allows in situ control of reversible assembly. Both the force magnitude and range vary with the solvent correlation length in a universal manner, adjusting with temperature from fractions of the thermal energy, k B T, and nanometre range to several ten kT and micrometer length scale. Combined with recent breakthroughs in the synthesis of complex particles, critical Casimir forces promise the design and assembly of complex colloidal structures, for fundamental studies of equilibrium and out-of-equilibrium phase behaviour. This review highlights recent developments in this evolving field, with special emphasis on the dynamic interaction control to assemble colloidal structures, in and out of equilibrium. PMID:26750980
Sample dependence of the Casimir forces
Pirozhenko, I; Svetovoy, V B
2006-01-01
We have analyzed available optical data for Au in the mid-infrared range which is important for a precise prediction of the Casimir force. Significant variation of the data demonstrates genuine sample dependence of the dielectric function. We demonstrate that the Casimir force is largely determined by the material properties in the low frequency domain and argue that therefore the precise values of the Drude parameters are crucial for an accurate evaluation of the force. These parameters can be estimated by two different methods, either by fitting real and imaginary parts of the dielectric function at low frequencies, or via a Kramers-Kronig analysis based on the imaginary part of the dielectric function in the extended frequency range. Both methods lead to very similar results. We show that the variation of the Casimir force calculated with the use of different optical data can be as large as 5% and at any rate cannot be ignored. To have a reliable prediction of the force with a precision of 1%, one has to m...
Finite difference computation of Casimir forces
Pinto, Fabrizio
2016-09-01
In this Invited paper, we begin by a historical introduction to provide a motivation for the classical problems of interatomic force computation and associated challenges. This analysis will lead us from early theoretical and experimental accomplishments to the integration of these fascinating interactions into the operation of realistic, next-generation micro- and nanodevices both for the advanced metrology of fundamental physical processes and in breakthrough industrial applications. Among several powerful strategies enabling vastly enhanced performance and entirely novel technological capabilities, we shall specifically consider Casimir force time-modulation and the adoption of non-trivial geometries. As to the former, the ability to alter the magnitude and sign of the Casimir force will be recognized as a crucial principle to implement thermodynamical nano-engines. As to the latter, we shall first briefly review various reported computational approaches. We shall then discuss the game-changing discovery, in the last decade, that standard methods of numerical classical electromagnetism can be retooled to formulate the problem of Casimir force computation in arbitrary geometries. This remarkable development will be practically illustrated by showing that such an apparently elementary method as standard finite-differencing can be successfully employed to numerically recover results known from the Lifshitz theory of dispersion forces in the case of interacting parallel-plane slabs. Other geometries will be also be explored and consideration given to the potential of non-standard finite-difference methods. Finally, we shall introduce problems at the computational frontier, such as those including membranes deformed by Casimir forces and the effects of anisotropic materials. Conclusions will highlight the dramatic transition from the enduring perception of this field as an exotic application of quantum electrodynamics to the recent demonstration of a human climbing
The role of magnetoplasmons in Casimir force calculations
Esquivel-Sirvent, R; Palomino-Ovando, M A; Cocoletzi, G H
2009-01-01
In this paper we review the role of magneto plasmon polaritons in the Casimir force calculations. By applying an external constant magnetic field a strong optical anisotropy is induced on two parallel slabs reducing the reflectivity and thus the Casimir force. As the external magnetic field increases, the Casimir force decreases. Thus, with an an external magnetic field the Casimir force can be controlled.The calculations are done in the Voigt configuration where the magnetic field is parallel to the slabs. In this configuration the reflection coefficients for TE and TM modes do not show mode conversion.
Probing the Casimir force with optical tweezers
Ether, D. S., Jr.; Pires, L. B.; Umrath, S.; Martinez, D.; Ayala, Y.; Pontes, B.; Araújo, G. R. de S.; Frases, S.; Ingold, G.-L.; Rosa, F. S. S.; Viana, N. B.; Nussenzveig, H. M.; Neto, P. A. Maia
2015-11-01
We propose to use optical tweezers to probe the Casimir interaction between microspheres inside a liquid medium for geometric aspect ratios far beyond the validity of the widely employed proximity force approximation. This setup has the potential for revealing unprecedented features associated to the non-trivial role of the spherical curvatures. For a proof of concept, we measure femtonewton double-layer forces between polystyrene microspheres at distances above 400 nm by employing very soft optical tweezers, with stiffness of the order of fractions of a fN/nm. As a future application, we propose to tune the Casimir interaction between a metallic and a polystyrene microsphere in saline solution from attraction to repulsion by varying the salt concentration. With those materials, the screened Casimir interaction may have a larger magnitude than the unscreened one. This line of investigation has the potential for bringing together different fields including classical and quantum optics, statistical physics and colloid science, while paving the way for novel quantitative applications of optical tweezers in cell and molecular biology.
Towards a Casimir force measurement between micromachined parallel plate structures
Syed Nawazuddin, M.B.; Lammerink, Theo S.J.; Berenschot, Erwin; Boer, de Meint; Ma, Ke-Chun; Elwenspoek, Miko C.; Wiegerink, Remco J.
2012-01-01
Ever since its prediction, experimental investigation of the Casimir force has been of great scientific interest. Many research groups have successfully attempted quantifying the force with different device geometries; however, measurement of the Casimir force between parallel plates with sub-micron
Casimir Forces due to Matters in Compactified Six Dimensions
Ito, M
2003-01-01
We calculate the Casimir energies due to matters with various boundary conditions along two compact directions in six-dimensional $T^{2}$ compactification. We discuss whether the Casimir forces are attractive or repulsive forces. On the theories with extra dimensions, the Casimir energy plays a crucial role in the mechanism for stabilizing the size of extra dimensions. Finally we argue a procedure of the application to $Z_{2}$ orbifold.
New Challenges and Directions in Casimir Force Experiments
Iannuzzi, Davide; Gelfand, Ian; Lisanti, Mariangela; Capasso, Federico
2003-01-01
This article is divided in three sections. In the first section we briefly review some high precision experiments on the Casimir force, underlying an important aspect of the analysis of the data. In the second section we discuss our recent results in the measurement of the Casimir force using non-trivial materials. In the third section we present some original ideas for experiments on new phenomena related to the Casimir effects.
Casimir-Polder forces on moving atoms
Scheel, Stefan
2009-01-01
Polarisable atoms and molecules experience the Casimir-Polder force near magnetoelectric bodies, a force that is induced by quantum fluctuations of the electromagnetic field and the matter. Atoms and molecules in relative motion to a magnetoelectric surface experience an additional, velocity-dependent force. We present a full quantum-mechanical treatment of this force and identify a generalised Doppler effect, the time delay between photon emission and reabsorption, and the Roentgen interaction as its three sources. For ground-state atoms, the force is very small and always decelerating, hence commonly known as quantum friction. For atom and molecules in electronically excited states, on the contrary, both decelerating and accelerating forces can occur depending on the magnitude of the atomic transition frequency relative to the surface plasmon frequency.
Repulsive Casimir force at zero and finite temperature
Energy Technology Data Exchange (ETDEWEB)
Lim, S C [Faculty of Engineering, Multimedia University, Jalan Multimedia, Cyberjaya, 63100 Selangor Darul Ehsan (Malaysia); Teo, L P [Faculty of Information Technology, Multimedia University, Jalan Multimedia, Cyberjaya, 63100 Selangor Darul Ehsan (Malaysia)], E-mail: sclim@mmu.edu.my, E-mail: lpteo@mmu.edu.my
2009-01-15
We study the zero and finite temperature Casimir force acting on a perfectly conducting piston with arbitrary cross section moving inside a closed cylinder with infinitely permeable walls. We show that at any temperature, the Casimir force always tends to move the piston away from the walls and toward its equilibrium position. In the case of a rectangular piston, exact expressions for the Casimir force are derived. In the high-temperature regime, we show that the leading term of the Casimir force is linear in temperature and therefore the Casimir force has a classical limit. Due to duality, all these results also hold for an infinitely permeable piston moving inside a closed cylinder with perfectly conducting walls.
Casimir forces between cylinders at different temperatures
Golyk, Vladyslav A; Reid, M T Homer; Kardar, Mehran
2012-01-01
We study Casimir interactions between cylinders in thermal non-equilibrium, where the objects as well as the environment are held at different temperatures. We provide the general formula for the force, in a one reflection approximation, for cylinders of arbitrary radii and optical properties. As is the case for equilibrium, we find that the force for optically diluted cylinders can be obtained by appropriate summation of the corresponding result for spheres. We find that the non-equilibrium forces are generally larger than their equilibrium counterpart at separations greater than the thermal wavelength. They may also exhibit oscillations as function of separation, leading to stable points of zero net force. These effects are particularly pronounced for thin conducting cylinders (e.g. 40nm diameter nano-wires of tungsten) due to their large emissivity.
Casimir forces from conductive silicon carbide surfaces
Sedighi, M.; Svetovoy, V. B.; Broer, W. H.; Palasantzas, G.
2014-05-01
Samples of conductive silicon carbide (SiC), which is a promising material due to its excellent properties for devices operating in severe environments, were characterized with the atomic force microscope for roughness, and the optical properties were measured with ellipsometry in a wide range of frequencies. The samples show significant far-infrared absorption due to concentration of charge carriers and a sharp surface phonon-polariton peak. The Casimir interaction of SiC with different materials is calculated and discussed. As a result of the infrared structure and beyond to low frequencies, the Casimir force for SiC-SiC and SiC-Au approaches very slowly the limit of ideal metals, while it saturates significantly below this limit if interaction with insulators takes place (SiC-SiO2). At short separations (<10 nm) analysis of the van der Waals force yielded Hamaker constants for SiC-SiC interactions lower but comparable to those of metals, which is of significance to adhesion and surface assembly processes. Finally, bifurcation analysis of microelectromechanical system actuation indicated that SiC can enhance the regime of stable equilibria against stiction.
Casimir-Polder Force Reversal with Metamaterials
Pappakrishnan, Venkatesh; Genov, Dentcho
2010-10-01
A promising system design aiming to demonstrate Casimir-Polder force (CPF) reversal is proposed. The constraints when using naturally available materials in designing the system with air as an intermediate medium is resolved by using artificial electromagnetic materials. The parametric space in terms of the plate's magnetic and dielectric plasma frequencies, gap thickness and temperature is investigated. The parametric domain for achieving CPF reversal is obtained. Furthermore, a simple analytical expression for the CPF is derived. The analytical expression accurately describes the large and short distance asymptotics and allows extraction of important parameters such as lower and upper cutoff gap distances that define the repulsive force window. This study could possibly lead us to design of quantum levitation system, frictionless bio-fluid transport devices, etc.
Casimir Force at a Knife's Edge
Graham, Noah; Emig, Thorsten; Rahi, Sahand Jamal; Jaffe, Robert L; Kardar, Mehran
2009-01-01
The Casimir force has been computed exactly for only a few simple geometries, such as infinite plates, cylinders, and spheres. We show that a parabolic cylinder, for which analytic solutions to the Helmholtz equation are available, is another case where such a calculation is possible. We compute the interaction energy of a parabolic cylinder and an infinite plate (both perfect mirrors), as a function of their separation and inclination, $H$ and $\\theta$, and the cylinder's parabolic radius $R$. As $H/R\\to 0$, the proximity force approximation becomes exact. The opposite limit of $R/H\\to 0$ corresponds to the a semi-infinite plate, where the effects of edge and inclination can be probed.
Oscillating Casimir force between two slabs in a Fermi sea
Institute of Scientific and Technical Information of China (English)
Chen Li-Weia; Su Guo-Zhen; Chen Jin-Can; Andresen Bjarne
2012-01-01
The Casimir effect for two parallel slabs immersed in an ideal Fermi sea is investigated at both zero and nonzero temperatures.It is found that the Casimir effect in a Fermi gas is distinctly different from that in an electromagnetic field or a massive Bose gas.In contrast to the familiar result that the Casimir force decreases monotonically with the increase of the separation L between two slabs in an electromagnetic field and a massive Bose gas,the Casimir force in a Fermi gas oscillates as a function of L.The Casimir force can be either attractive or repulsive,depending sensitively on the magnitude of L. In addition,it is found that the amplitude of the Casimir force in a Fermi gas decreases with the increase of the temperature,which also is contrary to the case in a Bose gas,since the bosonic Casimir force increases linearly with the increase of the temperature in the region T ＜ Tc,where Tc is the critical temperature of the Bose-Einstein condensation.
Strong Casimir force reduction through metallic surface nanostructuring
Intravaia, Francesco; Koev, Stephan; Jung, Il Woong; Talin, A. Alec; Davids, Paul S.; Decca, Ricardo S.; Aksyuk, Vladimir A.; Dalvit, Diego A. R.; López, Daniel
2013-09-01
The Casimir force between bodies in vacuum can be understood as arising from their interaction with an infinite number of fluctuating electromagnetic quantum vacuum modes, resulting in a complex dependence on the shape and material of the interacting objects. Becoming dominant at small separations, the force has a significant role in nanomechanics and object manipulation at the nanoscale, leading to a considerable interest in identifying structures where the Casimir interaction behaves significantly different from the well-known attractive force between parallel plates. Here we experimentally demonstrate that by nanostructuring one of the interacting metal surfaces at scales below the plasma wavelength, an unexpected regime in the Casimir force can be observed. Replacing a flat surface with a deep metallic lamellar grating with sub-100 nm features strongly suppresses the Casimir force and for large inter-surfaces separations reduces it beyond what would be expected by any existing theoretical prediction.
Collective behaviors of the Casimir force in microelectromechanical systems
Energy Technology Data Exchange (ETDEWEB)
Chan, H. B.; Yelton, J.
2013-01-23
Our goal was to explore the strong dependence of the Casimir force on the shape of the interacting bodies. We made significant progress and measured the Casimir force on silicon surface with rectangular corrugation and showed that the results agree with theoretical calculations, provided that the optical properties of silicon are taken into account. Furthermore, we performed measurement of the Casimir force within a single chip for the first time, between a doubly clamped beam and a movable, on-chip electrode at liquid helium temperature. This experiment represents a new way of studying the Casimir effect, a significant advance from the conventional approach of placing an external surface close to a force transducer.
Towards a Casimir Force Measurement between Micromachined Parallel Plate Structures
Directory of Open Access Journals (Sweden)
Remco J. Wiegerink
2012-11-01
Full Text Available Ever since its prediction, experimental investigation of the Casimir force has been of great scientific interest. Many research groups have successfully attempted quantifying the force with different device geometries; however, measurement of the Casimir force between parallel plates with sub-micron separation distance is still a challenging task, since it becomes extremely difficult to maintain sufficient parallelism between the plates. The Casimir force can significantly influence the operation of micro devices and to realize reliable and reproducible devices it is necessary to understand and experimentally verify the influence of the Casimir force at sub-micron scale. In this paper, we present the design principle, fabrication and characterization of micromachined parallel plate structures that could allow the measurement of the Casimir force with tunable separation distance in the range of 100 to 1000 nm. Initially, a gold coated parallel plate structure is explored to measure the Casimir force, but also other material combinations could be investigated. Using gold-silicon eutectic bonding, a reliable approach to bond chips with integrated suspended plates together with a well-defined separation distance in the order of 1–2 μm is developed.
Isoelectronic determination of the thermal Casimir force
Bimonte, G.; López, D.; Decca, R. S.
2016-05-01
Differential force measurements between spheres coated with either nickel or gold and rotating disks with periodic distributions of nickel and gold are reported. The rotating samples are covered by a thin layer of titanium and a layer of gold. While titanium is used for fabrication purposes, the gold layer (nominal thicknesses of 21, 37, 47, and 87 nm) provides an isoelectronic environment, and is used to nullify the electrostatic contribution but allow the passage of long wavelength Casimir photons. A direct comparison between the experimental results and predictions from Drude and plasma models for the electrical permittivity is carried out. In the models, the magnetic permeability of nickel is allowed to change to investigate its effects. Possible sources of errors, both in the experimental and theoretical sides, are taken into account. It is found that a Drude response with magnetic properties of nickel taken into account is unequivocally ruled out. The full analysis of the data indicates that a dielectric plasma response with the magnetic properties of Ni included shows good agreement with the data. Neither a Drude nor a plasma dielectric response provide a satisfactory description if the magnetic properties of nickel are disregarded.
Dynamics of thermal Casimir-Polder forces on polar molecules
Ellingsen, S. A.; Buhmann, S. Y.; Scheel, S.
2008-01-01
We study the influence of thermal Casimir-Polder forces on the near-surface trapping of cold polar molecules, with emphasis on LiH and YbF near an Au surface at room temperature. We show that for a molecule initially prepared in its electronic and rovibrational ground state, the Casimir-Polder force oscillates with the molecule-wall separation. The non-resonant force contribution and the evanescent part of the resonant force contribution almost exactly cancel at high temperature which results...
Repulsive Casimir force from fractional Neumann boundary conditions
Energy Technology Data Exchange (ETDEWEB)
Lim, S.C. [Faculty of Engineering, Multimedia University, Jalan Multimedia, 63100 Cyberjaya, Selangor (Malaysia)], E-mail: sclim@mmu.edu.my; Teo, L.P. [Faculty of Information Technology, Multimedia University, Jalan Multimedia, 63100 Cyberjaya, Selangor (Malaysia); Department of Applied Mathematics, Faculty of Engineering, University of Nottingham Malaysia Campus, Jalan Broga, 43500 Semenyih, Selangor Darul Ehsan (Malaysia)], E-mail: lpteo@mmu.edu.my
2009-08-17
This Letter studies the finite temperature Casimir force acting on a rectangular piston associated with a massless fractional Klein-Gordon field at finite temperature. Dirichlet boundary conditions are imposed on the walls of a d-dimensional rectangular cavity, and a fractional Neumann condition is imposed on the piston that moves freely inside the cavity. The fractional Neumann condition gives an interpolation between the Dirichlet and Neumann conditions, where the Casimir force is known to be always attractive and always repulsive respectively. For the fractional Neumann boundary condition, the attractive or repulsive nature of the Casimir force is governed by the fractional order which takes values from zero (Dirichlet) to one (Neumann). When the fractional order is larger than 1/2, the Casimir force is always repulsive. For some fractional orders that are less than but close to 1/2, it is shown that the Casimir force can be either attractive or repulsive depending on the aspect ratio of the cavity and the temperature.
Casimir switch: steering optical transparency with vacuum forces
Liu, X -f; Jing, H
2016-01-01
The Casimir force, originating from vacuum zero-point energy, is one of the most intriguing purely quantum effects. It has attracted renewed interests in current field of nanomechanics, due to the rapid size decrease of on-chip devices. Here we study the optomechanically-induced transparency (OMIT) with a tunable Casimir force. We find that the optical output rate can be significantly altered by the vacuum force, even terminated and then restored, indicating a highly-controlled optical switch. Our result addresses the possibility of designing exotic optical nano-devices by harnessing the power of vacuum.
Casimir switch: steering optical transparency with vacuum forces
Liu, Xi-Fang; Li, Yong; Jing, H.
2016-06-01
The Casimir force, originating from vacuum zero-point energy, is one of the most intriguing purely quantum effects. It has attracted renewed interests in current field of nanomechanics, due to the rapid size decrease of on-chip devices. Here we study the optomechanically-induced transparency (OMIT) with a tunable Casimir force. We find that the optical output rate can be significantly altered by the vacuum force, even terminated and then restored, indicating a highly-controlled optical switch. Our result addresses the possibility of designing exotic optical nano-devices by harnessing the power of vacuum.
Quantum field theory of the Casimir force for graphene
Klimchitskaya, G. L.
2016-01-01
We present theoretical description of the Casimir interaction in graphene systems which is based on the Lifshitz theory of dispersion forces and the formalism of the polarization tensor in (2+1)-dimensional space-time. The representation for the polarization tensor of graphene allowing the analytic continuation to the whole plane of complex frequencies is given. This representation is used to obtain simple asymptotic expressions for the reflection coefficients at all Matsubara frequencies and to investigate the origin of large thermal effect in the Casimir force for graphene. The developed theory is shown to be in a good agreement with the experimental data on measuring the gradient of the Casimir force between a Au-coated sphere and a graphene-coated substrate. The possibility to observe the thermal effect for graphene due to a minor modification of the already existing experimental setup is demonstrated.
The Casimir force control in nano and micro electromechanical systems
Sedighi Ghozotkhar, Mehdi
2016-01-01
In this thesis we deal with the analysis and measurement of dispersive surface forces, specifically the Casimir force. Applying Lifshitz theory makes it possible to take into account the material optical property and consequently the obtained results are more realistic. We used contact mode atomic f
Casimir Force Phase Transitions in the Graphene Family
Rodriguez-Lopez, Pablo; Dalvit, Diego A R; Woods, Lilia M
2016-01-01
The Casimir force is a universal interaction induced by electromagnetic quantum fluctuations between any types of objects. The expansion of the graphene family by adding silicene, germanene, and stanene, 2D allotropes of Si, Ge, and Sn, lands itself as a platform to probe Dirac-like physics in honeycomb staggered systems in such a ubiquitous interaction. We discover Casimir force phase transitions between these staggered 2D materials induced by the complex interplay between Dirac physics, spin-orbit coupling, and externally applied fields. In particular, we find that the interaction energy experiences different power law distance decays, magnitudes, and dependences on characteristic physical constants. Furthermore, due to the topological properties of these materials, repulsive and quantized Casimir interactions become possible.
Engineering Casimir force reduction through metallic surface nanostructuring
Intravaia, Francesco; Jung, Il Woong; Talin, A Alec; Davids, Paul S; Decca, Ricardo S; Aksyuk, Vladimir A; Dalvit, Diego A R; Lopez, Daniel
2012-01-01
The Casimir force is an interaction arising from quantum-mechanical fluctuations of the electromagnetic (EM) field, and is technologically significant as it results in stiction in micro- and nano-electromechanical systems (MEMS and NEMS). Control of the Casimir force has remained elusive, as many complex EM modes over a broad range of energy and length scales contribute simultaneously. Here we engineer one of two interacting gold surfaces into a high aspect ratio lamellar grating with 100 nm features, and demonstrate for the first time a strong Casimir force reduction by metallic nanostructuring. For inter-surface separations d above \\approx 400 nm, the measured Casimir force in vacuum decreases faster than the usual d^{-4} power-law reaching a value more than 2 times smaller than the one predicted by the proximity force approximation for planar-like geometries. The observed force suppression is in agreement with our ab-initio numerical analysis, and cannot be explained by either perfect electrical conductor ...
Electromagnetic Casimir Forces in Elliptic Cylinder Geometries
Graham, Noah
2013-01-01
The scattering theory approach makes it possible to carry out exact calculations of Casimir energies in any geometry for which the scattering T-matrix and a partial wave expansion of the free Green's function are available. We implement this program for the case of a perfectly conducting elliptic cylinder, thereby completing the set of geometries where electromagnetic scattering is separable. Particular emphasis is placed on the case of zero radius, where the elliptic cylinder reduces to a st...
Three-dimensional Casimir force between absorbing multilayer dielectrics
Raabe, C; Welsch, D G; Raabe, Christian; Kn\\"{o}ll, Ludwig; Welsch, Dirk-Gunnar
2003-01-01
Recently the influence of dielectric and geometrical properties on the Casimir force between dispersing and absorbing multilayered plates in the zero-temperature limit has been studied within a 1D quantization scheme for the electromagnetic field in the presence of causal media [R. Esquivel-Sirvent, C. Villarreal, and G.H. Cocoletzi, Phys. Rev. Lett. 64, 052108 (2001)]. In the present paper a rigorous 3D analysis is given, which shows that for complex heterostructures the 1D theory only roughly reflects the dependence of the Casimir force on the plate separation in general. Further, an extension of the very recently derived formula for the Casimir force at zero temperature [M.S. Toma\\v{s}, Phys. Rev. A 66, 052103 (2002)] to finite temperatures is given, and analytical expressions for specific distance laws in the zero-temperature limit are derived. In particular, it is shown that the Casimir force between two single-slab plates behaves asymptotically like $d^{-6}$ in place of $d^{-4}$ ($d$, plate separation).
Non-equilibrium Casimir force between vibrating plates.
Directory of Open Access Journals (Sweden)
Andreas Hanke
Full Text Available We study the fluctuation-induced, time-dependent force between two plates confining a correlated fluid which is driven out of equilibrium mechanically by harmonic vibrations of one of the plates. For a purely relaxational dynamics of the fluid we calculate the fluctuation-induced force generated by the vibrating plate on the plate at rest. The time-dependence of this force is characterized by a positive lag time with respect to the driving. We obtain two distinctive contributions to the force, one generated by diffusion of stress in the fluid and another related to resonant dissipation in the cavity. The relation to the dynamic Casimir effect of the electromagnetic field and possible experiments to measure the time-dependent Casimir force are discussed.
Non-equilibrium Casimir force between vibrating plates.
Hanke, Andreas
2013-01-01
We study the fluctuation-induced, time-dependent force between two plates confining a correlated fluid which is driven out of equilibrium mechanically by harmonic vibrations of one of the plates. For a purely relaxational dynamics of the fluid we calculate the fluctuation-induced force generated by the vibrating plate on the plate at rest. The time-dependence of this force is characterized by a positive lag time with respect to the driving. We obtain two distinctive contributions to the force, one generated by diffusion of stress in the fluid and another related to resonant dissipation in the cavity. The relation to the dynamic Casimir effect of the electromagnetic field and possible experiments to measure the time-dependent Casimir force are discussed. PMID:23326401
Long range Casimir force induced by transverse electromagnetic modes
Alvarez, Ezequiel
2009-01-01
We consider the interaction of two perfectly conducting plates of arbitrary shape that are inside a non-simply connected cylinder with transverse section of the same shape. We show that the existence of transverse electromagnetic (TEM) modes produces a Casimir force that decays only as $1/a^2$, where $a$ is the distance between plates. The TEM force does not depend on the area of the plates and dominates at large distances over the force produced by the transverse electric (TE) and transverse magnetic (TM) modes. These geometries provide a physical realization of the 1+1 dimensional Casimir effect. For the particular case of a coaxial circular cylindrical cavity, we compute the TE, TM and TEM contributions to the force, and find the critical distance for which the TEM modes dominate.
Proof that Casimir force does not originate from vacuum energy
Nikolic, H
2016-01-01
We present a simple general proof that Casimir force cannot originate from the vacuum energy of electromagnetic (EM) field. The full QED Hamiltonian consists of 3 terms: the pure electromagnetic term $H_{\\rm em}$, the pure matter term $H_{\\rm matt}$ and the interaction term $H_{\\rm int}$. The $H_{\\rm em}$-term commutes with all matter fields because it does not have any explicit dependence on matter fields. As a consequence, $H_{\\rm em}$ cannot generate any forces on matter. Since it is precisely this term that generates the vacuum energy of EM field, it follows that the vacuum energy does not generate the forces. The erroneous statements in the literature that vacuum energy generates Casimir force can be boiled down to the fact that $H_{\\rm em}$ attains an implicit dependence on matter fields by the use of the equations of motion and the erroneous treatment of the implicit dependence as if it was explicit. The true origin of the Casimir force is van der Waals force generated by $H_{\\rm int}$.
Casimir Force on Real Materials - the Slab and Cavity Geometry
Ellingsen, S A; Brevik, Iver; Ellingsen, Simen A.
2006-01-01
We analyse the potential of the geometry of a slab in a planar cavity for the purpose of Casimir force experiments. The force and its dependence on temperature, material properties and finite slab thickness are investigated both analytically and numerically for slab and walls made of aluminium and teflon FEP respectively. We conclude that such a setup is ideal for measurements of the temperature dependence of the Casimir force. By numerical calculation it is shown that temperature effects are dramatically larger for dielectrics, suggesting that a dielectric such as teflon FEP whose properties vary little within a moderate temperature range, should be considered for experimental purposes. We finally discuss the subtle but fundamental matter of the various Green's two-point function approaches present in the literature and show how they are different formulations describing the same phenomenon.
La force de Casimir et les plasmons de surface
Intravaia, F.; Lambrecht, A.; Reynaud, S.
2004-11-01
La présence de fluctuations irréductibles de champ dans le vide est une prédiction importante de la théorie quantique. Ces fluctuations ont de nombreux effets bien connus, dont l'archétype est la force de Casimir apparaîssant entre deux miroirs placés dans le vide par suite de la pression de radiation du vide. Elle a été récemment mesurée avec une précision de l'ordre du %. De nombreux travaux sont consacrés à l'évaluation théorique de cette force en visant une précision du même ordre. Ici nous étudions la force de Casimir dans la configuration de deux miroirs métalliques plans parallèles à température nulle. En supposant les miroirs décrits par un modèle plasma nous interprétons la force de Casimir comme le résultat de l'interaction entre les plasmons de surface des deux miroirs.
Casimir-like tunnelling-induced electronic forces
International Nuclear Information System (INIS)
We study the quantum forces that act between two nearby conductors due to electronic tunnelling. We derive an expression for these forces by calculating the flux of momentum arising from the overlap of evanescent electronic fields. Our result is written in terms of the electronic reflection amplitudes of the conductors and it has the same structure as Lifshitz's formula for the electromagnetically mediated Casimir forces. We evaluate the tunnelling force between two semiinfinite conductors and between two thin films separated by an insulating gap. We discuss some applications of our results
Material dependence of Casimir forces: gradient expansion beyond proximity
Bimonte, G; Kardar, M
2011-01-01
The widely used method for estimating Casimir interactions between gently curved material surfaces at short distances is the proximity force approximation (PFA). While this approximation is asymptotically exact at vanishing separations, quantifying corrections to PFA has been notoriously difficult. Here we use a derivative expansion to compute the leading curvature correction to PFA for metals (gold) and insulators (SiO$_2$) at room temperature. We derive an explicit expression for the amplitude $\\hat\\theta_1$ of the PFA correction to the force gradient for axially symmetric surfaces. In the non-retarded limit, the corrections to the Casimir free energy are found to scale logarithmically with distance. For gold, $\\hat\\theta_1$ has an unusually large temperature dependence.
Spatial dispersion in Casimir forces: a brief review
International Nuclear Information System (INIS)
We present the basic principles of non-local optics in connection with the calculation of the Casimir force between half-spaces and thin films. At currently accessible distances L, non-local corrections amount to about half a per cent, but they increase roughly as 1/L at smaller separations. Self-consistent models lead to corrections with the opposite sign as models with abrupt surfaces
An exact solution for the Casimir force in a spherically symmetric medium
Leonhardt, Ulf
2011-01-01
We calculated the force of the quantum vacuum, the Casimir force, in a spherically symmetric medium, Maxwell's fish eye, surrounded by a perfect mirror and derived an exact analytic solution. Our solution questions the idea that the Casimir force of a spherical mirror is repulsive - we found an attractive force that diverges at the mirror.
A veriﬁcation of quantum ﬁeld theory – measurement of Casimir force
Indian Academy of Sciences (India)
Anushree Roy; U Mohideen
2001-02-01
Here we review our work on measurement of the Casimir force between a large aluminum coated a sphere and ﬂat plate using an atomic force microscope. The average statistical precision is 1% of the force measured at the closest separation. We have also shown nontrival boundary dependence of the Casimir force.
Halving the Casimir force with conductive oxides: experimental details
de Man, Sven; Iannuzzi, Davide
2010-01-01
This work is an extended version of a paper published last year in Physical Review Letters [S. de Man et al., Phys. Rev. Lett. 103, 040402 (2009)], where we presented measurements of the Casimir force between a gold coated sphere and a plate coated with either gold or an indium-tin-oxide (ITO) layer. The experiment, which was performed in air, showed that ITO is sufficiently conducting to prevent charge accumulation, but still transparent enough to halve the Casimir attraction when compared to gold. Here, we report all the experimental details that, due to the limited space available, were omitted in the previous article. We discuss the performance of our setup in terms of stability of the calibration procedure and reproducibility of the Casimir force measurement. We also introduce and demonstrate a new technique to obtain the spring constant of our force sensor. Furthermore, we present a thorough description of the experimental method, a comprehensive explanation of data elaboration and error analysis, and a...
Energy Technology Data Exchange (ETDEWEB)
Ellingsen, Simen Andreas Aadnoey
2011-01-15
The present thesis focuses on several topics within three separate but related branches of the overall field of dispersion forces. The three branches are: temperature corrections to the Casimir force between real materials (Part 1), explicit calculation of Casimir energy in wedge geometries (Part 2), and Casimir-Polder forces on particles out of thermal equilibrium (Part 3). Part 1 deals primarily with analysis of a previously purported thermodynamic inconsistency in the Casimir-Lifshitz free energy of the interaction of two plane mirrors - violation of the third law of thermodynamics - when the latter's dielectric response is described with dissipative models. It is shown analytically and numerically that the Casimir entropy of the interaction between two metallic mirrors described by the Drude model does tend to zero at zero temperature, provided electronic relaxation does not vanish. The leading order terms at low temperature are found. A similar calculation is carried out for the interaction of semiconductors with small but non-zero DC conductivity. In a generalisation, it is shown that a violation of the third law can only occur for permittivities whose low-frequency behaviour is temperature dependent near zero temperature. A calculation using path integral methods shows that the low temperature behaviour of the interaction of fluctuating Foucault currents in two mirrors of Drude metal is identical to that of the full Casimir-Lifshitz free energy, reasserting a previous finding by Intravaia and Henkel that such fluctuating bulk currents are the physical reason for the anomalous entropy behaviour. In a related effort, an analysis of the frequency dependence of the Casimir force by Ford is generalised to imperfectly reflecting mirrors. A paradox is pointed out, in that the effects of a perturbation of the reflecting properties of the mirrors in a finite frequency window can be calculated in two ways giving different results. It is concluded that optimistic
The Casimir Forces in a Single Conducting Cylindrical Cavity
Razmi, H
2013-01-01
We want to study the Casimir effect for a single conducting microscopic cylindrical cavity. The mathematical technique is based on the Green function of the geometry of the inside of the cavity, and the integral regularization is based on the plasma frequency cutoff for real conductors. Using the symmetric electromagnetic energy-momentum tensor, in terms of four potential, the total Casimir energy for the inside of the Cavity is calculated. Considering the fundamental cutoff applied by the uncertainty relations' limit on virtual particles' frequency in the quantum vacuum, it is shown that the contribution of the external (outside of the cavity) Casimir energy is negligible. Finally, the forces experienced by the lateral surface of the cavity and its circular bases are calculated. The resulting expressions show that these forces are repulsive. The numerical computation is done for the real problem of a cavity with a basis of a radius in the same order of its height at the scale of 100 nanometers made of the be...
What is credible and what is incredible in the measurements of the Casimir force
Klimchitskaya, G L
2010-01-01
We comment on progress in measurements of the Casimir force and discuss what is the actual reliability of different experiments. In this connection a more rigorous approach to the usage of such concepts as accuracy, precision, and measure of agreement between experiment and theory, is presented. We demonstrate that all measurements of the Casimir force employing spherical lenses with centimeter-size curvature radii are fundamentally flawed due to the presence of bubbles and pits on their surfaces. The commonly used formulation of the proximity force approximation is shown to be inapplicable for centimeter-size lenses. New expressions for the Casimir force are derived taking into account surface imperfections. Uncontrollable deviations of the Casimir force from the values predicted using the assumption of perfect sphericity vary by a few tens of percent within the separation region from 1 to $3\\,\\mu$m. This makes impractical further use of centimeter-size lenses in experiments on measuring the Casimir force.
Precision measurement of the Casimir-Lifshitz force in a fluid
Munday, Jeremy N
2007-01-01
The Casimir force, which results from the confinement of the quantum mechanical zero-point fluctuations of the electromagnetic fields, has received significant attention in recent years for its effect on micro- and nano-scale mechanical systems. With few exceptions, experimental observations have been limited to conductive bodies interacting separated by vacuum or air. However, interesting phenomena including repulsive forces are expected to exist in certain circumstances between metals and dielectrics when the intervening medium is not vacuum. In order to better understand the effect of the Casimir force in such situations and to test the robustness of the generalized Casimir-Lifshitz theory, we have performed the first precision measurements of the Casimir force between two metals immersed in a fluid. For this situation, the measured force is attractive and is approximately 80% smaller than the force predicted by Casimir for ideal metals in vacuum. We present experimental results and find them to be consist...
Influence of materials' optical response on actuation dynamics by Casimir forces
Sedighi Ghozotkhar, Mehdi; Broer, W. H.; Van der Veeke, S.; Svetovoy, V. B.; Palasantzas, G.
2015-01-01
The dependence of the Casimir force on the frequency-dependent dielectric functions of interacting materials makes it possible to tailor the actuation dynamics of microactuators. The Casimir force is largest for metallic interacting systems due to the high absorption of conduction electrons in the f
Casimir forces from conductive silicon carbide surfaces
Sedighi Ghozotkhar, Mehdi; Svetovoy, V. B.; Broer, W. H.; Palasantzas, G.
2014-01-01
Samples of conductive silicon carbide (SiC), which is a promising material due to its excellent properties for devices operating in severe environments, were characterized with the atomic force microscope for roughness, and the optical properties were measured with ellipsometry in a wide range of fr
The role of the "Casimir force analogue" at the microscopic processes of crystallization and melting
Chuvildeev, V. N.; Semenycheva, A. V.
2016-10-01
Melting (crystallization), a phase transition from a crystalline solid to a liquid state, is a common phenomenon in nature. We suggest a new factor, "the Casimir force analogue", to describe mechanisms of melting and crystallization. The Casimir force analogue is a force occurring between the surfaces of solid and liquid phases of metals caused by different energy density of phonons of these phases. It explains abrupt changes in geometry and thermodynamic parameters at a melting point. "The Casimir force analogue" helps to estimate latent melting heat and to gain an insight into a solid-liquid transition problem.
Constraints on stable equilibria with fluctuation-induced (Casimir) forces.
Rahi, Sahand Jamal; Kardar, Mehran; Emig, Thorsten
2010-08-13
We examine whether fluctuation-induced forces can lead to stable levitation. First, we analyze a collection of classical objects at finite temperature that contain fixed and mobile charges and show that any arrangement in space is unstable to small perturbations in position. This extends Earnshaw's theorem for electrostatics by including thermal fluctuations of internal charges. Quantum fluctuations of the electromagnetic field are responsible for Casimir or van der Waals interactions. Neglecting permeabilities, we find that any equilibrium position of items subject to such forces is also unstable if the permittivities of all objects are higher or lower than that of the enveloping medium, the former being the generic case for ordinary materials in vacuum. PMID:20868024
Repulsive and Restoring Casimir Forces Based on Magneto-Optical Effect
Institute of Scientific and Technical Information of China (English)
ZENG Ran; YANG Ya-Ping
2011-01-01
The Casimir force direction tuned by the external magnetic field due to the magneto-optical Voigt effect is investigated. The magneto-optical effect gives rise to the modified frequency-dependent electric permittivity and thus the electromagnetic properties of the materials can be adjusted to satisfy the condition of the formation of repulsive Casimir force. It is found that between the ordinary dielectric slab and magneto-optical material slab, a repulsive force may exist by adjusting the applied magnetic field. The restoring Casimir force can also be obtained if suitable parameter values are taken. For realistic materials, the repulsive and the restoring force is shown to possibly take place at typical distances in microelectromechanical systems.%@@ The Casimir force direction tuned by the external magnetic field due to the magneto-optical Voigt effect is investigated.The magneto-optical effect gives rise to the modified frequency-dependent electric permittivity and thus the electromagnetic properties of the materials can be adjusted to satisfy the condition of the formation of repulsive Casimir force.It is found that between the ordinary dielectric slab and magneto-optical material slab,a repulsive force may exist by adjusting the applied magnetic field.The restoring Casimir force can also be obtained if suitable parameter values are taken.For realistic materials,the repulsive and the restoring force is shown to possibly take place at typical distances in microelectromechanical systems.
Towards a precision measurement of the Casimir force in a cylinder-plane geometry
Brown-Hayes, Michael; Dalvit, Diego A. R.; Mazzitelli, Francisco D.; Kim, Woo-Joong; Onofrio, Roberto
2005-01-01
We report on a proposal aimed at measuring the Casimir force in a cylinder-plane configuration. The Casimir force is evaluated including corrections due to finite parallelism, conductivity, and temperature. The range of validity of the proximity force approximation is also discussed. An apparatus to test the feasibility of a precision measurement in this configuration has been developed, and we describe both a procedure to control the parallelism and the results of the electrostatic calibrati...
Thermal fluctuations and stability of a particle levitated by a repulsive Casimir force in a liquid.
Inui, Norio; Goto, Kosuke
2013-11-01
We study the vertical Brownian motion of a gold particle levitated by a repulsive Casimir force to a silica plate immersed in bromobenzene. The time evolution of the particle distribution starting from an equilibrium position, where the Casimir force and gravitational force are balanced, is considered by solving the Langevin equation using the Monte Carlo method. When the gold particle is very close to the silica plate, the Casimir force changes from repulsive to attractive, and the particle eventually sticks to the surface. The escape rate from a metastable position is calculated by solving the Fokker-Plank equation; it agrees with the value obtained by Kramers' escape theory. The duration of levitation increases as the particle radius increases up to around 2.3 μm. As an example, we show that a 1-μm-diameter gold particle can be levitated for a significantly long time by the repulsive Casimir force at room temperature.
Casimir Force of Piston Systems with Arbitrary Cross Sections under Different Boundary Conditions
Institute of Scientific and Technical Information of China (English)
XIONG Ai-Min; CHEN Xiao-Song
2009-01-01
We study the Casimir force between two pistons under different boundary conditions inside an infinite cylinder with arbitrary cross section.It is found that the attractive or repulsive character of the Casimir force for a scalar field is determined only by the boundary condition along the longitudinal direction and is independent of the cross section,transverse boundary conditions and the mass of the field.Under symmetric Dirichlet-Dirichlet,Neumann-Neumann and periodic longitudinal boundary conditions the Casimir force is always attractive,but is repulsive under non-symmetric Dirichlet-Neumann and anti-periodic longitudinal boundary conditions.The Casimir force of the electromagnetic field in an ideal conductive piston is also investigated.This force is always attractive regardless of the shape of the cross section and the transverse boundary conditions.
Sedighi, M.; Broer, W. H.; Palasantzas, G.; Kooi, B. J.
2013-10-01
Amorphous to crystalline phase transitions in phase change materials (PCM) can have strong influence on the actuation of microelectromechanical systems under the influence of Casimir forces. Indeed, the bifurcation curves of the stationary equilibrium points and the corresponding phase portraits of the actuation dynamics between gold and AIST (Ag5In5Sb60Te30) PCM, where an increase of the Casimir force of up ˜25% has been measured upon crystallization, show strong sensitivity to changes of the Casimir force as the stiffness of the actuating component decreases and/or the effective interaction area of the Casimir force increases, which can also lead to stiction. However, introduction of intrinsic energy dissipation (associated with a finite quality factor of the actuating system) can prevent stiction by driving the system to attenuated motion towards stable equilibrium depending on the PCM state and the system quality factor.
Casimir force in brane worlds: Coinciding results from Green's and zeta function approaches
International Nuclear Information System (INIS)
Casimir force encodes the structure of the field modes as vacuum fluctuations and so it is sensitive to the extra dimensions of brane worlds. Now, in flat spacetimes of arbitrary dimension the two standard approaches to the Casimir force, Green's function, and zeta function yield the same result, but for brane world models this was only assumed. In this work we show that both approaches yield the same Casimir force in the case of universal extra dimensions and Randall-Sundrum scenarios with one and two branes added by p compact dimensions. Essentially, the details of the mode eigenfunctions that enter the Casimir force in the Green's function approach get removed due to their orthogonality relations with a measure involving the right hypervolume of the plates, and this leaves just the contribution coming from the zeta function approach. The present analysis corrects previous results showing a difference between the two approaches for the single brane Randall-Sundrum; this was due to an erroneous hypervolume of the plates introduced by the authors when using the Green's function. For all the models we discuss here, the resulting Casimir force can be neatly expressed in terms of two four-dimensional Casimir force contributions: one for the massless mode and the other for a tower of massive modes associated with the extra dimensions.
Casimir force on a piston at finite temperature in Randall-Sundrum models
Institute of Scientific and Technical Information of China (English)
CHENG Hong-Bo
2011-01-01
The Casimir effect for a three-parallel-plate system at finite temperature within the framework of five-dimensional Randall-Sundrum models is studied.In the case of the Randall-Sundrum model involving two branes we find that the Casimir force depends on the plate distance and temperature after one outer plate has been moved to a distant place.Further we discover that the sign of the reduced force is negative if the plate and piston are located close together,but the nature of reduced force becomes repulsive when the plate distance is not very small and finally the repulsive force vanishes with extremely large plate separation.A higher temperature causes a greater repulsive Casimir force.Within the framework of a one-brane scenario the reduced Casimir force between the piston and one plate remains attractive no matter how high the temperature is.It is interesting that a stronger thermal effect leads to a greater attractive Casimir force instead of changing the nature of the force.
Casimir force on a piston at finite temperature in Randall-Sundrum models
International Nuclear Information System (INIS)
The Casimir effect for a three-parallel-plate system at finite temperature within the framework of five-dimensional Randall-Sundrum models is studied. In the case of the Randall-Sundrum model involving two branes we find that the Casimir force depends on the plate distance and temperature after one outer plate has been moved to a distant place. Further we discover that the sign of the reduced force is negative if the plate and piston are located close together, but the nature of reduced force becomes repulsive when the plate distance is not very small and finally the repulsive force vanishes with extremely large plate separation. A higher temperature causes a greater repulsive Casimir force. Within the framework of a one-brane scenario the reduced Casimir force between the piston and one plate remains attractive no matter how high the temperature is. It is interesting that a stronger thermal effect leads to a greater attractive Casimir force instead of changing the nature of the force. (author)
Modifying the Casimir force between indium tin oxide film and Au sphere
Banishev, A A; Castillo-Garza, R; Klimchitskaya, G L; Mostepanenko, V M; Mohideen, U; 10.1103/PhysRevB.85.045436
2012-01-01
We present complete results of the experiment on measuring the Casimir force between an Au-coated sphere and an untreated or, alternatively, UV-treated indium tin oxide film deposited on a quartz substrate. Measurements were performed using an atomic force microscope in a high vacuum chamber. The measurement system was calibrated electrostatically. Special analysis of the systematic deviations is performed, and respective corrections in the calibration parameters are introduced. The corrected parameters are free from anomalies discussed in the literature. The experimental data for the Casimir force from two measurement sets for both untreated and UV-treated samples are presented. The experimental errors are determined at a 95% confidence level. It is demonstrated that the UV treatment of an I TO plate results in a significant decrease in the magnitude of the Casimir force (from 21% to 35% depending on separation). However, ellipsometry measurements of the imaginary parts of dielectric permittivities of the un...
Kelvin probe force microscopy of metallic surfaces used in Casimir force measurements
Behunin, R. O.; Dalvit, D. A. R.; Decca, R. S.; Genet, C.; Jung, I. W.; Lambrecht, A.; Liscio, A.; López, D.; Reynaud, S.; Schnoering, G.; Voisin, G.; Zeng, Y.
2014-12-01
Kelvin probe force microscopy at normal pressure was performed by two different groups on the same Au-coated planar sample used to measure the Casimir interaction in a sphere-plane geometry. The obtained voltage distribution was used to calculate the separation dependence of the electrostatic pressure Pres(D ) in the configuration of the Casimir experiments. In the calculation it was assumed that the potential distribution in the sphere has the same statistical properties as the measured one, and that there are no correlation effects on the potential distributions due to the presence of the other surface. The result of this calculation, using the currently available knowledge, is that Pres(D ) does not explain the magnitude or the separation dependence of the difference Δ P (D ) between the measured Casimir pressure and the one calculated using a Drude model for the electromagnetic response of Au. We discuss in the conclusions the points which have to be checked out by future work, including the influence of pressure and a more accurate determination of the patch distribution, in order to confirm these results.
Influence of materials' optical response on actuation dynamics by Casimir forces
Sedighi, M.; Broer, W. H.; Van der Veeke, S.; Svetovoy, V. B.; Palasantzas, G.
2015-06-01
The dependence of the Casimir force on the frequency-dependent dielectric functions of interacting materials makes it possible to tailor the actuation dynamics of microactuators. The Casimir force is largest for metallic interacting systems due to the high absorption of conduction electrons in the far-infrared range. For less conductive systems, such as phase change materials or conductive silicon carbide, the reduced force offers the advantage of increased stable operation of MEMS devices against pull-in instabilities that lead to unwanted stiction. Bifurcation analysis with phase portraits has been used to compare the sensitivity of a model actuator when the optical properties are altered.
The imperfect Bose gas in d dimensions: critical behavior and Casimir forces
International Nuclear Information System (INIS)
We consider the d-dimensional imperfect (mean-field) Bose gas confined in a slit-like geometry and subject to periodic boundary conditions. Within an exact analytical treatment we first extract the bulk critical properties of the system at Bose–Einstein condensation and identify the bulk universality class to be the one of the classical d-dimensional spherical model. Subsequently we consider finite slit width D and analyze the excess surface free energy and the related Casimir force acting between the slit boundaries. Above the bulk condensation temperature (T > Tc) the Casimir force decays exponentially as a function of D, with the bulk correlation length determining the relevant length scale. For T = Tc and for T c its decay is algebraic. The magnitude of the Casimir forces at Tc and for T c is governed by the universal Casimir amplitudes. We extract the relevant values for different d and compute the scaling functions describing the crossover between the critical and low-temperature asymptotics of the Casimir force. The scaling function is monotonic at any d∈(2,4) and becomes constant for d > 4 and T ≤ Tc. (paper)
Critical adsorption and critical Casimir forces in the canonical ensemble.
Gross, Markus; Vasilyev, Oleg; Gambassi, Andrea; Dietrich, S
2016-08-01
Critical properties of a liquid film between two planar walls are investigated in the canonical ensemble, within which the total number of fluid particles, rather than their chemical potential, is kept constant. The effect of this constraint is analyzed within mean-field theory (MFT) based on a Ginzburg-Landau free-energy functional as well as via Monte Carlo simulations of the three-dimensional Ising model with fixed total magnetization. Within MFT and for finite adsorption strengths at the walls, the thermodynamic properties of the film in the canonical ensemble can be mapped exactly onto a grand canonical ensemble in which the corresponding chemical potential plays the role of the Lagrange multiplier associated with the constraint. However, due to a nonintegrable divergence of the mean-field order parameter profile near a wall, the limit of infinitely strong adsorption turns out to be not well-defined within MFT, because it would necessarily violate the constraint. The critical Casimir force (CCF) acting on the two planar walls of the film is generally found to behave differently in the canonical and grand canonical ensembles. For instance, the canonical CCF in the presence of equal preferential adsorption at the two walls is found to have the opposite sign and a slower decay behavior as a function of the film thickness compared to its grand canonical counterpart. We derive the stress tensor in the canonical ensemble and find that it has the same expression as in the grand canonical case, but with the chemical potential playing the role of the Lagrange multiplier associated with the constraint. The different behavior of the CCF in the two ensembles is rationalized within MFT by showing that, for a prescribed value of the thermodynamic control parameter of the film, i.e., density or chemical potential, the film pressures are identical in the two ensembles, while the corresponding bulk pressures are not. PMID:27627242
Critical adsorption and critical Casimir forces in the canonical ensemble
Gross, Markus; Vasilyev, Oleg; Gambassi, Andrea; Dietrich, S.
2016-08-01
Critical properties of a liquid film between two planar walls are investigated in the canonical ensemble, within which the total number of fluid particles, rather than their chemical potential, is kept constant. The effect of this constraint is analyzed within mean-field theory (MFT) based on a Ginzburg-Landau free-energy functional as well as via Monte Carlo simulations of the three-dimensional Ising model with fixed total magnetization. Within MFT and for finite adsorption strengths at the walls, the thermodynamic properties of the film in the canonical ensemble can be mapped exactly onto a grand canonical ensemble in which the corresponding chemical potential plays the role of the Lagrange multiplier associated with the constraint. However, due to a nonintegrable divergence of the mean-field order parameter profile near a wall, the limit of infinitely strong adsorption turns out to be not well-defined within MFT, because it would necessarily violate the constraint. The critical Casimir force (CCF) acting on the two planar walls of the film is generally found to behave differently in the canonical and grand canonical ensembles. For instance, the canonical CCF in the presence of equal preferential adsorption at the two walls is found to have the opposite sign and a slower decay behavior as a function of the film thickness compared to its grand canonical counterpart. We derive the stress tensor in the canonical ensemble and find that it has the same expression as in the grand canonical case, but with the chemical potential playing the role of the Lagrange multiplier associated with the constraint. The different behavior of the CCF in the two ensembles is rationalized within MFT by showing that, for a prescribed value of the thermodynamic control parameter of the film, i.e., density or chemical potential, the film pressures are identical in the two ensembles, while the corresponding bulk pressures are not.
Colloidal aggregation in microgravity by critical Casimir forces
Veen, Sandra; Schall, Peter; Antoniuk, Oleg; Potenza, Marco; Alaimo, Matteo; Mazzoni, Stefano; Wegdam, Gerard
2012-02-01
We study aggregation and crystal growth of spherical Teflon colloids in binary liquid mixtures in microgravity by the critical Casimir effect. The critical Casimir effect induces interactions between colloids due to the confinement of bulk fluctuations (density or concentration) near the critical point of liquids. The strength and range of the interaction depends on the length scale of these fluctuations which increase as one approaches the critical point. The interaction potential can thus be tuned with temperature. We follow the growth of structures in real time with Near Field Scattering. Measurements are performed in microgravity in order to study pure diffusion limited aggregation, without disturbance by sedimentation or flow.
Lamoreaux, Steve; Wong, Douglas
2015-06-01
The basic theory of temporal mechanical fluctuation induced systematic errors in Casimir force experiments is developed and applications of this theory to several experiments is reviewed. This class of systematic error enters in a manner similar to the usual surface roughness correction, but unlike the treatment of surface roughness for which an exact result requires an electromagnetic mode analysis, time dependent fluctuations can be treated exactly, assuming the fluctuation times are much longer than the zero point and thermal fluctuation correlation times of the electromagnetic field between the plates. An experimental method for measuring absolute distance with high bandwidth is also described and measurement data presented.
International Nuclear Information System (INIS)
The basic theory of temporal mechanical fluctuation induced systematic errors in Casimir force experiments is developed and applications of this theory to several experiments is reviewed. This class of systematic error enters in a manner similar to the usual surface roughness correction, but unlike the treatment of surface roughness for which an exact result requires an electromagnetic mode analysis, time dependent fluctuations can be treated exactly, assuming the fluctuation times are much longer than the zero point and thermal fluctuation correlation times of the electromagnetic field between the plates. An experimental method for measuring absolute distance with high bandwidth is also described and measurement data presented. (paper)
Sedighi, Mehdi; Palasantzas, George
2014-02-01
Casimir and hydrodynamic dissipation forces can strongly influence the actuation of microelectromechanical systems in ambient conditions. The dissipative and stiction dynamics of an actuating system is shown to depend on surface physical processes related to fluid slip and the size of the actuating components. Using phase change materials the Casimir force magnitude can be modulated via amorphous-crystalline phase transitions. The dissipative motion between amorphous coated phase change material components can be changed towards stiction upon crystallization and suitable choice of restoring spring constants. By contrast, amorphization can augment switching from stiction to dissipative dynamics.
Force sensor for chameleon and Casimir force experiments with parallel-plate configuration
Almasi, Attaallah; Iannuzzi, Davide; Sedmik, René I P
2015-01-01
The search for non-Newtonian forces has been pursued following many different paths. Recently it was suggested that hypothetical chameleon interactions, which might explain the mechanisms behind dark energy, could be detected in a high-precision force measurement. In such an experiment, interactions between parallel plates kept at constant separation could be measured as a function of the pressure of an ambient gas, thereby identifying chameleon interactions by their unique inverse dependence on the local mass density. During the past years we have been developing a new kind of setup complying with the high requirements of the proposed experiment. In this article we present the first and most important part of this setup -- the force sensor. We discuss its design, fabrication, and characterization. From the results of the latter we derive limits on chameleon interaction parameters that could be set by the forthcoming experiment. Finally, we describe the opportunity to use the same setup to measure Casimir for...
Casimir force between planes as a boundary finite size effect
International Nuclear Information System (INIS)
The ground state energy of a boundary quantum field theory is derived in planar geometry in D+1-dimensional spacetime. It provides a universal expression for the Casimir energy which exhibits its dependence on the boundary conditions via the reflection amplitudes of the low energy particle excitations. We demonstrate the easy and straightforward applicability of the general expression by analyzing the free scalar field with Robin boundary condition and by rederiving the most important results available in the literature for this geometry
Sedighi, Mehdi; Palasantzas, George
2015-04-01
The role of the Casimir force on the analysis of microactuators is strongly influenced by the optical properties of interacting materials. Bifurcation and phase portrait analysis were used to compare the sensitivity of actuators when the optical properties at low optical frequencies were modeled using the Drude and Plasma models. Indeed, for metallic systems, which have strong Casimir attraction, the details of the modeling of the low optical frequency regime can be dramatic, leading to predictions of either stable motion or stiction instability. However, this difference is strongly minimized for weakly conductive systems as are the doped insulators making actuation modeling more certain to predict.
Energy Technology Data Exchange (ETDEWEB)
Dalvit, Diego A1 [Los Alamos National Laboratory; Rodriguez, Alejandro W [MASS INST OF TECH; Munday, J N [HARVARD UNIV; Joannopoulos, J D [MASS INST OF TECH
2008-01-01
Using accurate numerical methods for finite-size nonplanar objects, we demonstrate a stable mechanical suspension of a silica cylinder within a metallic cylinder separated by ethanol, via a repulsive Casimir force between the silica and the metal. We investigate cylinders with both circular and square cross sections, and show that the latter exhibit a stable orientation as well as a stable position, employing a new method to accurately compute Casimir torques for finite objects. Furthermore, the stable orientation of the square cylinder is shown to undergo an unusual 45 transition as a function of the separation lengthscale, and this transition is explained as a consequence of material dispersion.
Broer, W.; Palasantzas, G.; Knoester, J.; Svetovoy, V.B.
2012-01-01
So far there has been no reliable method to calculate the Casimir force at separations comparable to the root-mean square of the height fluctuations of the surfaces. Statistical analysis of rough gold samples has revealed the presence of peaks considerably higher than the root-mean-square roughness.
Bordag, M; Mostepanenko, V M
1997-01-01
We calculate the constraints on the constants of hypothetical long-range interactions which follow from the recent measurement of the Casimir force. A comparison with previous constraints is given. The new constraints are up to a factor of 3000 stronger in some parameter regions .
Sedighi Ghozotkhar, Mehdi; Broer, W. H.; Palasantzas, G.; Kooi, B. J.
2013-01-01
Amorphous to crystalline phase transitions in phase change materials (PCM) can have strong influence on the actuation of microelectromechanical systems under the influence of Casimir forces. Indeed, the bifurcation curves of the stationary equilibrium points and the corresponding phase portraits of
Sedighi Ghozotkhar, Mehdi; Palasantzas, Georgios
2015-01-01
The role of the Casimir force on the analysis of microactuators is strongly influenced by the optical properties of interacting materials. Bifurcation and phase portrait analysis were used to compare the sensitivity of actuators when the optical properties at low optical frequencies were modeled usi
Sedighi Ghozotkhar, Mehdi; Palasantzas, Georgios
2014-01-01
Casimir and hydrodynamic dissipation forces can strongly influence the actuation of microelectromechanical systems in ambient conditions. The dissipative and stiction dynamics of an actuating system is shown to depend on surface physical processes related to fluid slip and the size of the actuating
Kramers-Kronig relations for plasma-like permittivities and the Casimir force
Klimchitskaya, G L; Mostepanenko, V M
2007-01-01
The Kramers-Kronig relations are derived for the permittivity of the usual plasma model which neglects dissipation and of a generalized model which takes into account the interband transitions. The generalized plasma model is shown to be consistent with all precision experiments on the measurement of the Casimir force.
Non-monotonic thermal Casimir force from geometry-temperature interplay
Weber, Alexej; Gies, Holger
2010-01-01
The geometry dependence of Casimir forces is significantly more pronounced in the presence of thermal fluctuations due to a generic geometry-temperature interplay. We show that the thermal force for standard sphere-plate or cylinder-plate geometries develops a non-monotonic behavior already in the simple case of a fluctuating Dirichlet scalar. In particular, the attractive thermal force can increase for increasing distances below a critical temperature. This anomalous behavior is triggered by...
Institute of Scientific and Technical Information of China (English)
郑茂盛; 周根树; 赵文轸; 顾海澄
2002-01-01
Casimir force and residual stresses actually appear in over-layers or films simultaneously. The study of the behaviour of micro- and nano-electromechanical systems in the presence of Casimir force and residual stress is of significance to the design of the relevant devices. We derive analytical expressions of the deflection of a bridge-shaped device under the mutual actions of Casimir force and residual stress in films. It is shown that the tensile residual stress enhances wavy behaviour of the deflection, while the compressive residual stress increases the deflection value and reduces the wavy behaviour.
Casimir forces in multilayer magnetodielectrics with both gain and loss
DEFF Research Database (Denmark)
Amooghorban, Ehsan; Wubs, Martijn; Mortensen, N. Asger;
2011-01-01
A path-integral approach to the quantization of the electromagnetic field in a linearly amplifying magnetodielectric medium is presented. Two continua of inverted harmonic oscillators are used to describe the polarizability and magnetizability of the amplifying medium. The causal susceptibilities...... of the amplifying medium, with negative imaginary parts in finite frequency intervals, are identified and their relationships to microscopic coupling functions are determined. By carefully relating the two-point functions of the field theory to the optical Green functions, we calculate the Casimir...
Rederivation of the Casimir force under the completeness relation of continuum operator
Xianlong, Gao
2016-01-01
Casimir effects manifests that, the two closely paralleled plates, generally produce a macroscopic attractive force due to the quantum vacuum fluctuations of the electromagnetic fields. The derivation of the force requires an {\\it artificial} regulator by removing the divergent summation. By including naturally a spectrum density factor, based on the observation that an incomplete eigenvectors of observable, such as the eigenstates for the photons in the free field, can form a complete set of eigenvectors by introducing a unique spectrum transformation, an alternative way is presented to rederive the force, without using a regulator. As a result, the Casimir forces are obtained with the first term $-\\pi^2 \\hbar c/(240 a^4)$ attractive, and the second one, $-\\pi^4 \\hbar c^3 \\sigma^2/(1008 a^6)$, also attractive but smaller, with $a$ the plate separation, and $\\sigma$ a to-be-determined small constant number in the spectrum density factor.
Comment on ``Precision measurement of the Casimir-Lifshitz force in a fluid''
Geyer, B; Mohideen, U; Mostepanenko, V M
2007-01-01
Recently J.N. Munday and F. Capasso [Phys. Rev. A {\\bf 75}, 060102(R) (2007); arXiv:0705.3793] claimed that they have performed a precision measurement of the Casimir force between a sphere and a plate coated with Au, both immersed in ethanol. The measurement results were claimed to be consistent with the Lifshitz theory. We demonstrate that in this paper the Casimir force between the smooth surfaces of the test bodies was computed inaccurately with an error of up to 25%. We show also that the attractive electrostatic force only due to the surface potential differences was underestimated by a factor of 590 and the charge double layer interaction was not taken into account. All this leads to the conclusion that the results of this experiment are in fact uncertain.
Casimir force between two parallel semiconductor slabs: Magnetic field effects in the Voigt geometry
Energy Technology Data Exchange (ETDEWEB)
Garcia-Serrano, R.; Palomino-Ovando, M. [Facultad de Ciencias Fisico-Matematicas, Universidad Autonoma de Puebla, Puebla (Mexico); Martinez, G.; Hernandez, P.H.; Cocoletzi, Gregorio H. [Instituto de Fisica, Universidad Autonoma de Puebla, Puebla (Mexico)
2009-06-15
We investigate the Casimir force F between two parallel semiconductor slabs taking into account magnetoplasmon effects. For our calculations we consider an external magnetic field applied in the Voigt geometry. Studies are carried out using the formula of F, which is written in terms of the reflectivities of the incident electromagnetic (EM) waves onto the surfaces of the semiconductor slabs, in the vacuum gap between slabs. Results show that the Casimir force depends strongly on the slab thickness as well as on the magnetic-field strength (or equivalently on the cyclotron frequency). At a constant cyclotron frequency and for small slab thickness F/F{sub 0} (F{sub 0} is the ideal force) displays a dip at small separation distances L between slabs. F/F{sub 0} increases with L up to saturation as the slab thickness increases. The curve with the strongest value of F/F{sub 0} corresponds to the semi-infinite medium geometry. For a constant slab thickness and small cyclotron frequency, F/F{sub 0} as a function of L shows a monotonic increase as L increases, and eventually reaches saturation. At high cyclotron frequency F/F{sub 0} displays a dip. The curve of F/F{sub 0} with no applied external field corresponds to the one with the strongest Casimir force. Therefore, magnetoplasmon effects, with an applied magnetic field in the Voigt geometry may inhibit the Casimir force. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Esteso, Victoria; Carretero-Palacios, Sol; Míguez, Hernán
2016-04-01
We study at thermal equilibrium the effect of temperature deviations around room temperature on the equilibrium distance (deq) at which thin films made of Teflon, silica, or polystyrene immersed in glycerol levitate over a silicon substrate due to the balance of Casimir, gravity, and buoyancy forces. We find that the equilibrium nature (stable or unstable) of deq is preserved under temperature changes, and provide simple rules to predict whether the new equilibrium position will occur closer to or further from the substrate at the new temperature. These rules depend on the static permittivities of all materials comprised in the system ( ɛ0 ( m ) ) and the equilibrium nature of deq. Our designed dielectric configuration is excellent for experimental observation of thermal effects on the Casimir force indirectly detected through the tunable equilibrium distances (with slab thickness and material properties) in levitation mode.
Casimir Forces via Worldline Numerics: Method Improvements and Potential Engineering Applications
Aehlig, Klaus; Fischbacher, Thomas; Gerhard, Jochen
2011-01-01
The string theory inspired Worldline Numerics approach to Casimir force calculations has some favourable characteristics that might make it well suited for geometric optimization problems as they arise e.g. in NEMS device engineering. We explain this aspect in detail, developing some refinements of the method along the way. Also, we comment on the problem of generalizing Worldline Numerics from scalars to photons in the presence of conductors.
Algebraic approach to multiple defects on the line and application to Casimir force
Mintchev, M
2007-01-01
An algebraic framework for quantization in presence of arbitrary number of point-like defects on the line is developed. We consider a scalar field which interacts with the defects and freely propagates away of them. As an application we compute the Casimir force both at zero and finite temperature. We derive also the charge density in the Gibbs state of a complex scalar field with defects. The example of two delta-defects is treated in detail.
Institute of Scientific and Technical Information of China (English)
翟向华; 李新洲
2011-01-01
卡什米尔效应起源于量子场的真空涨落,其正则化需要用到多种数学手段,它在物理学的各个分支,特别是当前在纳米技术中有着重要的应用.这是一个多学科交叉的研究领域,经过了60多年由慢到快的发展之后,当前,它是一个充满挑战和活力的前沿研究领域,有许多未决问题等待人们去探索.%The Casimir effect is a macroscopic quantum effect due to the disturbance of the vacuum of the quantum field. It is a multiinterdisciplinary subject. It plays an important role in a variety of fields of physics in the application in nanotechnology at present. After the development of more than 60 years, it is still a very live challenging research field, leaving a lot of open questions for us to explore.
Stable levitation and alignment of compact objects by Casimir spring forces.
Rahi, Sahand Jamal; Zaheer, Saad
2010-02-19
We investigate a stable Casimir force configuration consisting of an object contained inside a spherical or spheroidal cavity filled with a dielectric medium. The spring constant for displacements from the center of the cavity and the dependence of the energy on the relative orientations of the inner object and the cavity walls are computed. We find that the stability of the force equilibrium-unlike the direction of the torque-can be predicted based on the sign of the force between two slabs of the same material. PMID:20366865
The proximity force approximation for the Casimir energy as a derivative expansion
Fosco, C D; Mazzitelli, F D
2011-01-01
The proximity force approximation (PFA) has been widely used as a tool to evaluate the Casimir force between smooth objects at small distances. In spite of being intuitively easy to grasp, it is generally believed to be an uncontrolled approximation. Indeed, its validity has only been tested in particular examples, by confronting its predictions with the next to leading order (NTLO) correction extracted from numerical or analytical solutions obtained without using the PFA. In this article we show that the PFA and its NTLO correction may be derived within a single framework, as the first two terms in a derivative expansion. To that effect, we consider the Casimir energy for a vacuum scalar field with Dirichlet conditions on a smooth curved surface described by a function $\\psi$ in front of a plane. By regarding the Casimir energy as a functional of $\\psi$, we show that the PFA is the leading term in a derivative expansion of this functional. We also obtain the general form of corresponding NTLO correction, whi...
Surface-impedance approach solves problems with the thermal Casimir force between real metals
Geyer, B; Mostepanenko, V M
2003-01-01
The surface impedance approach to the description of the thermal Casimir effect in the case of real metals is elaborated starting from the free energy of oscillators. The Lifshitz formula expressed in terms of the dielectric permittivity depending only on frequency is shown to be inapplicable in the frequency region where a real current may arise leading to Joule heating of the metal. The standard concept of a fluctuating electromagnetic field on such frequencies meets difficulties when used as a model for the zero-point oscillations or thermal photons in the thermal equilibrium inside metals. Instead, the surface impedance permits not to consider the electromagnetic oscillations inside the metal but taking the realistic material properties into account by means of the effective boundary condition. An independent derivation of the Lifshitz-type formulas for the Casimir free energy and force between two metal plates is presented within the impedance approach. It is shown that they are free of the contradiction...
Casimir force in the O(n -> infinity) model with free boundary conditions
Dantchev, Daniel; Bergknoff, Jonathan; Rudnick, Joseph
2012-01-01
We present results for the temperature behavior of the Casimir force for a system with a film geometry with thickness $L$ subject to free boundary conditions and described by the $n\\to\\infty$ limit of the $O(n)$ model. These results extend over all temperatures, including the critical regime near the bulk critical temperature $T_c$, where the critical fluctuations determine the behavior of the force, and temperatures well below it, where its behavior is dictated by the Goldstone's modes contr...
Approximating the effect of the Casimir force on the instability of electrostatic nano-cantilevers
Energy Technology Data Exchange (ETDEWEB)
Abadyan, Mohamadreza [Islamic Azad University, Tonekabon Branch, Ramsar Center, Ramsar (Iran, Islamic Republic of); Novinzadeh, Alireza [Aerospace Engineering Department, K N Toosi University of Technology, East Vafadar Street, PO Box 16765-3381, Tehran (Iran, Islamic Republic of); Kazemi, AsiehSadat [School of Physics and Center for Solid State Research, Damghan University of Basic Sciences, PO Box 367164-167, Damghan (Iran, Islamic Republic of)], E-mail: novinzadeh@kntu.ac.ir
2010-01-15
In this paper, the homotopy perturbation method (HPM) is used to investigate the effect of the Casimir force on the pull-in instability of electrostatic actuators at nano-scale separations. The proposed HPM is employed to solve nonlinear constitutive equations of cantilever beam-type nanoactuators. An analytical solution is obtained in terms of convergent series with easily computable components. Basic design parameters such as critical cantilever tip deflection and pull-in voltage of the nano-cantilevers are computed. As special cases of this work, freestanding nanoactuators and electrostatic micro-actuators are investigated. The analytical HPM results agree well with numerical solutions and those from the literature.
Casimir force between $\\delta-\\delta^{\\prime}$ mirrors transparent at high frequencies
Braga, Alessandra N; Alves, Danilo T
2016-01-01
We investigate, in the context of a real massless scalar field in $1+1$ dimensions, models of partially reflecting mirrors simulated by Dirac $\\delta-\\delta^{\\prime}$ point interactions. In the literature, these models do not exhibit full transparency at high frequencies. In order to provide a more realistic feature for these models, we propose a modified $\\delta-\\delta^{\\prime}$ point interaction that enables to achieve full transparency in the limit of high frequencies. Taking this modified $\\delta-\\delta^{\\prime}$ model into account, we investigate the Casimir force, comparing our results with those found in the literature.
Lateral-drag Casimir forces induced by anisotropy
Nefedov, Igor S
2016-01-01
We predict the existence of lateral drag forces near the flat surface of an absorbing slab of an anisotropic material. The forces originate from the fluctuations of the electromagnetic field, when the anisotropy axis of the material forms a certain angle with the surface. In this situation, the spatial spectra of the fluctuating electromagnetic fields becomes asymmetric, different for positive and negative transverse wave vectors components. Differently from the case of van der Waals interactions in which the forward-backward symmetry is broken due to the particle movement or in quantum noncontact friction where it is caused by the mutual motion of the bodies, in our case the lateral motion results merely from the anisotropy of the slab. This new effect, of particular significance in hyperbolic materials, could be used for the manipulation of nanoparticles.
Bimonte, Giuseppe
2010-01-01
The possibility of making precise predictions for the Casimir force is essential for addressing the striking contradiction that has arisen between the a new large distance Casimir experiment with gold plates, that has been interpreted as being consistent with the so-called Drude prescription and to rule out the plasma prescription, and a series of older precise short distance experiments, which were instead interpreted as being consistent with the plasma prescription and to rule out the Drude one. In a previous paper by the author [Phys. Rev. A {\\bf 81}, 062501 (2010)] it was shown that a precise prediction of the Casimir force is possible in principle by a simple modification of the standard Kramers-Kronig relations, involving suitable analytic window functions, solely on the basis of experimental optical data in the frequency interval where they are available, without using uncontrolled data extrapolations towards zero frequency that are necessary with standard Kramers-Kronig relations. In the present paper...
Casimir Force between a Small Dielectric Sphere and a Dielectric Wall
Sopova, V
2004-01-01
The possibility of repulsive Casimir forces between small metal spheres and a dielectric half-space is discussed. We treat a model in which the spheres have a dielectric function given by the Drude model, and the radius of the sphere is small compared to the corresponding plasma wavelength. The half-space is also described by the same model, but with a different plasma frequency. We find that in the retarded limit, the force is quasi-oscillatory. This leads to the prediction of stable equilibrium points at which the sphere could levitate in the Earth's gravitational field. This seems to lead to the possibility of an experimental test of the model. The effects of finite temperature on the force are also studied, and found to be rather small at room temperature. However, thermally activated transitions between equilibrium points could be significant at room temperature.
Casimir force in the O(n→∞) model with free boundary conditions.
Dantchev, Daniel; Bergknoff, Jonathan; Rudnick, Joseph
2014-04-01
We present results for the temperature behavior of the Casimir force for a system with a film geometry with thickness L subject to free boundary conditions and described by the n→∞ limit of the O(n) model. These results extend over all temperatures, including the critical regime near the bulk critical temperature Tc, where the critical fluctuations determine the behavior of the force, and temperatures well below it, where its behavior is dictated by the Goldstone mode contributions. The temperature behavior when the absolute temperature, T, is a finite distance below Tc, up to a logarithmic-in-L proximity of the bulk critical temperature, is obtained both analytically and numerically; the critical behavior follows from numerics. The results resemble-but do not duplicate-the experimental curve behavior for the force obtained for He4 films. PMID:24827202
Farrokhabadi, Amin; Abadian, Naeime; Rach, Randolph; Abadyan, Mohamadreza
2014-09-01
The Casimir force can induce instability and adhesion in freestanding nanostructures. Previous research efforts in this area have exclusively focused on modeling the instability in structures with planar or rectangular cross-section, while, to the best knowledge of the authors, no attention has been paid to investigate this phenomenon for nanowires with circular cross-section. In this study, effects of the Casimir force on the instability and adhesion of freestanding Cylinder-Plate and Cylinder-Cylinder geometries are investigated, which are commonly encountered in real nanodevices. To compute the Casimir force, two approaches, i.e. the proximity force approximation (PFA) for small separations and Dirichlet asymptotic approximation (scattering theory) for large separations, are considered. A continuum mechanics theory is employed, in conjunction with the Euler-beam model, to obtain constitutive equations of the systems. The governing nonlinear constitutive equations of the nanostructures are solved using two different approaches, i.e. the analytical modified Adomian decomposition (MAD) and the numerical finite difference method (FDM). The detachment length and minimum gap, both of which prevent the Casimir force-induced adhesion, are computed for both configurations.
Casimir energy and force induced by an impenetrable flux tube of finite radius
Gorkavenko, V M; Stepanov, O B
2013-01-01
A perfectly reflecting (Dirichlet) boundary condition at the edge of an impenetrable magnetic-flux-carrying tube of nonzero transverse size is imposed on the charged massive scalar matter field which is quantized outside the tube. We show that the vacuum polarization effects outside the tube give rise to a macroscopic force acting at the increase of the tube radius (if the magnetic flux is held steady). The Casimir energy and force are periodic in the value of the magnetic flux, being independent of the coupling to the space-time curvature scalar. We conclude that a topological defect of the vortex type can polarize the vacuum of only those quantum fields that have masses which are much less than a scale of the spontaneous symmetry breaking.
Sympathetic laser-cooling of graphene with Casimir-Polder forces
Ribeiro, Sofia
2016-01-01
We propose a scheme to actively cool the fundamental flexural (out-of-plane) mode of a graphene sheet via vacuum forces. Our setup consists in a cold atom cloud placed close to a graphene sheet at distances of a few micrometers. The atoms couple to the graphene membrane via Casimir-Polder forces. By deriving a self-consistent set of equations governing the dynamics of the atomic gas and the flexural modes of the graphene, we show to be possible to cool graphene from room temperatures by actively (laser) cooling an atomic gas. By choosing the right set of experimental parameter we are able to cool a graphene sheet down to ~ 60 microkelvin.
Lamoreaux, Steve K.
2010-01-01
Several new experiments have extended studies of the Casimir force into new and interesting regimes. This recent work will be briefly reviewed. With this recent progress, new issues with background electrostatic effects have been uncovered. The myriad of problems associated with both patch potentials and electrostatic calibrations are discussed and the remaining open questions are brought forward.
Casimir force between a half-space and a plate of finite thickness
Høye, Johan S.; Brevik, Iver
2016-05-01
Zero-frequency Casimir theory is analyzed from different viewpoints, with the aim of obtaining further insight into the delicate Drude-plasma issue that turns up when one considers thermal corrections to the Casimir force. The problem is essentially that the plasma model, physically inferior in comparison to the Drude model since it leaves out dissipation in the material, apparently gives the best results when comparing with recent experiments. Our geometric setup is quite conventional, namely, a dielectric plate separated from a dielectric half-space by a vacuum gap, both media being made of the same material. Our investigation is divided into the following categories: (1) Making use of the statistical-mechanical method developed by J. S. Høye and I. Brevik [Physica A (Amsterdam, Neth.) 259, 165 (1998), 10.1016/S0378-4371(98)00249-0], implying that the quantized electromagnetic field is replaced by interaction between dipole moments oscillating in harmonic potentials, we first verify that the Casimir force is in agreement with the Drude prediction. No use of Fresnel's reflection coefficients is made at this stage. (2) Then turning to the field-theoretic description implying use of the reflection coefficients, we derive results in agreement with the forgoing when first setting the frequency equal to zero, before letting the permittivity become large. With the plasma relation the reflection coefficient for TE zero-frequency modes depends on the component of the wave vector parallel to the surfaces and lies between 0 and 1. This contradicts basic electrostatic theory. (3) Turning to high-permeability magnetic materials, the TE zero-frequency mode describes the static magnetic field in the same way the TM zero-frequency modes describe the static electric fields in electrostatics. With the plasma model magnetic fields, except for a small part, cannot pass through metals; that is, metals effectively become superconductors. However, recent experimental results clearly
Electromagnetic Casimir Forces of Parabolic Cylinder and Knife-Edge Geometries
Graham, Noah; Emig, Thorsten; Rahi, Sahand Jamal; Jaffe, Robert L; Kardar, Mehran
2011-01-01
An exact calculation of electromagnetic scattering from a perfectly conducting parabolic cylinder is employed to compute Casimir forces in several configurations. These include interactions between a parabolic cylinder and a plane, two parabolic cylinders, and a parabolic cylinder and an ordinary cylinder. To elucidate the effect of boundaries, special attention is focused on the "knife-edge" limit in which the parabolic cylinder becomes a half-plane. Geometrical effects are illustrated by considering arbitrary rotations of a parabolic cylinder around its focal axis, and arbitrary translations perpendicular to this axis. A quite different geometrical arrangement is explored for the case of an ordinary cylinder placed in the interior of a parabolic cylinder. All of these results extend simply to nonzero temperatures.
International Nuclear Information System (INIS)
We report constraints on the parameters of Yukawa-type corrections to Newtonian gravity from measurements of the gradient of the Casimir force in the configuration of an Au-coated sphere above a Si plate covered with corrugations of trapezoidal shape. For this purpose, the exact expression for the gradient of Yukawa force in the experimental configuration is derived and compared with that obtained using the proximity force approximation. The reported constraints are of almost the same strength as those found previously from several different experiments on the Casimir force and extend over a wide interaction range from 30 to 1260 nm. It is discussed how to make them stronger by replacing the material of the plate.
Classification of the sign of the critical Casimir force in two dimensional systems
Rajabpour, M A
2016-01-01
We classify the sign of the critical Casimir force between two finite objects separated by a large distance in the two dimensional systems that can be described by conformal field theory (CFT). In particular, we show that as far as the smallest scaling dimension present in the spectrum of the system is smaller than one, the sign of the force is independent of the shape of the objects and can be determined by the elements of the modular $S$-matrix of the CFT. The provided formula for the sign of the force indicates that the force is always attractive for equal boundary conditions independent of the shape of the objects. However, different boundary conditions can lead to attractive or repulsive forces. Using the derived formula, we prove the known results regarding the Ising model and the free bosons. As new examples, we give detailed results regarding the Q=3-states Potts model and the compactified bosons. In particular, for the latter model we show that Dirichlet boundary condition does not always lead to an ...
Measurement of the Casimir force between a spherical gold tip and Si(111)-(7 × 7) surfaces
Yoshida, Naoki; Higashino, Kazuhiko; Sueoka, Kazuhisa
2016-08-01
We have performed the measurement of Casimir force between a spherical Au tip and an atomically flat Si(111)-(7 × 7) surface at tip–sample distances ranging from 15 to 50 nm in an ultrahigh vacuum of 1.5 × 10‑8 Pa by frequency-modulation atomic force microscopy. Atomically flat Si(111) surfaces provided by the ultrahigh-vacuum condition and a degassed Au tip reduce the contact potential difference that must be compensated. These experimental conditions led to the elucidation of the distance dependence of the Casimir force down to the distance of 15 nm. The observed distance dependence still follows a theory provided by Chen et al. [Phys. Rev. A 74, 022103 (2006)] within these distances.
Observation of reduction in Casimir force without change of dielectric permittivity
Banishev, A A; Castillo-Garza, R; Klimchitskaya, G L; Mostepanenko, V M; Mohideen, U
2012-01-01
Additional information is provided on the effect of the significant (up to 35%) reduction in the magnitude of the Casimir force between an Au-coated sphere and an indium tin oxide film which was observed after UV treatment of the latter. A striking feature of this effect is that the reduction is not accompanied with a corresponding variation of the dielectric permittivity, as confirmed by direct ellipsometry measurements. The measurement data are compared with computations using the Lifshitz theory. It is shown that the data for the untreated sample are in a very good agreement with theory taking into account the free charge carriers in the indium tin oxide. The data for the UV-treated sample exclude the theoretical results obtained with account of free charge carriers. These data are found to be in a very good agreement with theory disregarding the free charge carriers in an indium tin oxide film. A possible theoretical explanation of our observations as a result of phase transition of indium tin oxide from ...
Klimchitskaya, G L; Mostepanenko, V M
2012-01-01
We derive constraints on corrections to Newtonian gravity of the Yukawa type and light elementary particles from two recently performed measurements of the gradient of the Casimir force. In the first measurement the configuration of two Au surfaces has been used, whereas in the second a nonmagnetic metal Au interacted with a magnetic metal Ni. In these configurations one arrives at different, respectively, similar theoretical predictions for the Casimir force when the competing theoretical approaches are employed. Nevertheless, we demonstrate that the constraints following from both experiments are in mutual agreement and in line with constraints obtained from earlier measurements. This confirms the reliability of constraints on non-Newtonian gravity obtained from measurements of the Casimir force.
Nonlinear (Anharmonic Casimir Oscillator
Directory of Open Access Journals (Sweden)
Habibollah Razmi
2011-01-01
Full Text Available We want to study the dynamics of a simple linear harmonic micro spring which is under the influence of the quantum Casimir force/pressure and thus behaves as a (an nonlinear (anharmonic Casimir oscillator. Generally, the equation of motion of this nonlinear micromechanical Casimir oscillator has no exact solvable (analytical solution and the turning point(s of the system has (have no fixed position(s; however, for particular values of the stiffness of the micro spring and at appropriately well-chosen distance scales and conditions, there is (are approximately sinusoidal solution(s for the problem (the variable turning points are collected in a very small interval of positions. This, as a simple and elementary plan, may be useful in controlling the Casimir stiction problem in micromechanical devices.
Experiment and theory in the Casimir effect
Klimchitskaya, G L
2006-01-01
Casimir effect is the attractive force which acts between two plane parallel, closely spaced, uncharged, metallic plates in vacuum. This phenomenon was predicted theoretically in 1948 and reliably investigated experimentally only in recent years. In fact, the Casimir force is similar to the familiar van der Waals force in the case of relatively large separations when the relativistic effects come into play. We review the most important experiments on measuring the Casimir force by means of torsion pendulum, atomic force microscope and micromechanical torsional oscillator. Special attention is paid to the puzzle of the thermal Casimir force, i.e., to the apparent violation of the third law of thermodynamics when the Lifshitz theory of dispersion forces is applied to real metals. Thereafter we discuss the role of the Casimir force in nanosystems including the stiction phenomenon, actuators, and interaction of hydrogen atoms with carbon nanotubes. The applications of the Casimir effect for constraining predictio...
Teo, L P
2013-01-01
We derive analytically the asymptotic behavior of the Casimir interaction between a sphere and a plate when the distance between them, $d$, is much smaller than the radius of the sphere, $R$. The leading order and next-to-leading order terms are derived from the exact formula for the Casimir interaction energy. They are found to depend nontrivially on the dielectric functions of the objects. As expected, the leading order term coincides with that derived using the proximity force approximation. The result on the next-to-leading order term complements that found by Bimonte, Emig and Kardar [Appl. Phys. Lett. \\textbf{100}, 074110 (2012)] using derivative expansion. Numerical results are presented when the dielectric functions are given by the plasma model or the Drude model, with the plasma frequency (for plasma and Drude models) and relaxation frequency (for Drude model) given respectively by 9eV and 0.035eV, the conventional values used for gold metal. It is found that if plasma model is used instead of Drude...
Chen, Xiang
2012-11-01
We investigate the net force on a rigid Casimir cavity generated by vacuum fluctuations of electromagnetic field in three cases: de Sitter space-time, de Sitter space-time with weak gravitational field and Schwarzschild-de Sitter space-time. In de Sitter space-time the resulting net force follows the square inverse law but unfortunately it is too weak to be measurable due to the large universe radius. By introducing a weak gravitational field into the de Sitter space-time, we find that the net force can now be split into two parts, one is the gravitational force due to the induced effective mass between the two plates and the other one is generated by the metric structure of de Sitter space-time. In order to investigate the vacuum fluctuation force on the rigid cavity under strong gravitational field, we perform a similar analysis in Schwarzschild-de Sitter space-time and results are obtained in three different limits. The most interesting one is when the cavity gets closer to the horizon of a blackhole, square inverse law is recovered and the repulsive force due to negative energy/mass of the cavity now has an observable strength. More importantly the force changes from being repulsive to attractive when the cavity crosses the event horizon, so that the energy/mass of the cavity switches the sign, which suggests the unusual time direction inside the event horizon.
Casimir-Polder force between anisotropic nanoparticles and gently curved surfaces
Bimonte, Giuseppe; Emig, Thorsten; Kardar, Mehran
2015-07-01
The Casimir-Polder interaction between an anisotropic particle and a surface is orientation dependent. We study novel orientational effects that arise due to curvature of the surface for distances much smaller than the radii of curvature by employing a derivative expansion. For nanoparticles we derive a general short distance expansion of the interaction potential in terms of their dipolar polarizabilities. Explicit results are presented for nano-spheroids made of SiO2 and gold, both at zero and at finite temperatures. The preferred orientation of the particle is strongly dependent on curvature, temperature, as well as material properties.
Chen, Xiang
2012-01-01
We investigate the net force on a rigid Casimir cavity generated by vacuum fluctuations of electromagnetic field in three cases, de Sitter spacetime, de Sitter spacetime with weak gravitational field and Schwarzschild-de Sitter spacetime. In de Sitter spacetime the resulting net force follows the square inverse law but unfortunately it is too weak to be measurable due to the large universe radius. By introducing a weak gravitational field into the de Sitter spacetime, we find the net force now can be splited into two parts, one is the gravitational force due to the induced effective mass between the two plates, the other one is generated by the metric structure of de Sitter spacetime. In order to investigate the vacuum fluctuation force on the rigid cavity under strong gravitational field, we perform the similar analysis in Schwarzschild-de Sitter spacetime, results are obtained in three different limits. The most interesting one is when the cavity gets closer to the horizon of a blackhole, square inverse law...
Finite Temperature Casimir Effect for Corrugated Plates
Institute of Scientific and Technical Information of China (English)
ZHAO Yan; SHAO Cheng-Gang; LUO Jun
2006-01-01
@@ Using the path-integral method, the corrections to the Casimir energy due to the combined effect of surface roughness and the finite temperature are calculated. For the specific case of two sinusoidally corrugated plates,the lateral Casimir force at finite temperature is obtained. The amplitude of the lateral Casimir force has a maximum at an optimal wavelength of λ≈ 2H with the mean plate distance H. This optimal parameter relation is almost independent of temperature.
Casimir force for a scalar field in a single brane world
International Nuclear Information System (INIS)
Vacuum force is an interesting low energy test for brane worlds due to its dependence on field's modes and its role in submillimeter gravity experiments. In this contribution we obtain the scalar field vacuum force between two parallel plates lying in the brane of a Randall-Sundrum scenario extended by p compact dimensions (RSII-p). We obtain the force using the Green's function technique and we compare our results with the ones obtained by using the zeta function regularization method. As a result we obtain agreement in the expression for the force independently of the method used, thus we solve a previous discrepancy between the two approaches.
Mode Contributions to the Casimir Effect
Intravaia, F.; Henkel, C.
2010-04-01
Applying a sum-over-modes approach to the Casimir interaction between two plates with finite conductivity, we isolate and study the contributions of surface plasmons and Foucault (eddy current) modes. We show in particular that for the TE-polarization eddy currents provide a repulsive force that cancels, at high temperatures, the Casimir free energy calculated with the plasma model.
Mode contributions to the Casimir effect
Intravaia, Francesco
2009-01-01
Applying a sum-over-modes approach to the Casimir interaction between two plates with finite conductivity, we isolate and study the contributions of surface plasmons and Foucault (eddy current) modes. We show in particular that for the TE-polarization eddy currents provide a repulsive force that cancels, at high temperatures, the Casimir free energy calculated with the plasma model.
Casimir effect for Elko spinor field
Pereira, S H; Santos, Rubia dos
2016-01-01
The Casimir effect for the Elko spinor field in $3+1$ dimension is obtained using Dirichlet boundary conditions. It is shown the existence of a repulsive force four times greater than the case of the scalar field. The precise reason for such differences are highlighted and interpreted, as well as the right parallel of the Casimir effect due to scalar and fermionic fields.
Casimir-Polder forces on atoms in the presence of magnetoelectronic bodies
Energy Technology Data Exchange (ETDEWEB)
Buhmann, S.Y.
2007-07-05
In this work, the CP force between a single neutral atom or molecule and neutral magnetoelectric bodies is studied. The focus lies on the pure vacuum CP force, i.e., the electromagnetic field is in general understood to be in its ground state. Furthermore, we assume that the atom-body separation is sufficiently large to ensure that the atom is adequately characterised as an electric dipole, while the body can be described by its macroscopic magnetoelectric properties; and that repulsive exchange forces due to the overlap between the electronic wave functions of the atom and the bodies can be neglected. Interactions due to non-vanishing net charges, permanent electric dipole moments, magnetisability, quadrupole (or higher multipole) polarisabilities of the atom and those resulting from non-local or anisotropic magnetoelectric properties of the bodies are ignored. (orig.)
Fermions on the low-buckled honey-comb structured lattice plane and classical Casimir-Polder force
Goswami, Partha
2016-05-01
We start with the well-known expression for the vacuum polarization and suitably modify it for 2+1-dimensional spin-orbit coupled (SOC) fermions on the low-buckled honey-comb structured lattice plane described by the low-energy Liu-Yao-Feng-Ezawa (LYFE) model Hamiltonian involving the Dirac matrices in the chiral representation obeying the Clifford algebra. The silicene and germanene fit this description suitably. They have the Dirac cones similar to those of graphene and SOC is much stronger. The system could be normal or ferromagnetic in nature. The silicene turns into the latter type if there is exchange field arising due to the proximity coupling to a ferromagnet (FM) such as depositing Fe atoms to the silicene surface. For the silicene, we find that the many-body effects considerably change the bare Coulomb potential by way of the dependence of the Coulomb propagator on the real-spin, iso-spin and the potential due to an electric field applied perpendicular to the silicene plane. The computation aspect of the Casimir-Polder force (CPF) needs to be investigated in this paper. An important quantity in this process is the dielectric response function (DRF) of the material. The plasmon branch was obtained by finding the zeros of DRF in the long-wavelength limit. This leads to the plasmon frequencies. We find that the collective charge excitations at zero doping, i.e., intrinsic plasmons, in this system, are absent in the Dirac limit. The valley-spin-split intrinsic plasmons, however, come into being in the case of the massive Dirac particles with characteristic frequency close to 10 THz. Our scheme to calculate the Casimir-Polder interaction (CPI) of a micro-particle with a sheet involves replacing the dielectric constant of the sample in the CPI expression obtained on the basis of the Lifshitz theory by the static DRF obtained using the expressions for the polarization function we started with. Though the approach replaces a macroscopic constant by a microscopic
The Reality of Casimir Friction
Milton, K A; Brevik, I
2015-01-01
For more than 35 years theorists have studied quantum or Casimir friction, which occurs when two smooth bodies move transversely to each other, experiencing a frictional dissipative force due to quantum fluctuations. These forces are typically very small, unless the bodies are nearly touching, and consequently such effects have never been observed, although lateral Casimir forces have been seen for corrugated surfaces. Because of the lack of contact with phenomena, theoretical predictions for the frictional force between parallel plates, or between a polarizable atom and a metallic plate, have varied widely. Here we review the history of these calculations, show that theoretical consensus is emerging, and offer some hope that it might be possible to experimentally confirm this phenomenon of dissipative quantum electrodynamics.
Nonequilibrium Tuning of the Thermal Casimir Effect
Dean, David S; Maggs, A C; Podgornik, Rudolf
2016-01-01
In net-neutral systems correlations between charge fluctuations generate strong attractive thermal Casimir forces and engineering these forces to optimize nanodevice performance is an important challenge. We show how the normal and lateral thermal Casimir forces between two plates containing Brownian charges can be modulated by decorrelating the system through the application of an electric field, which generates a nonequilibrium steady state with a constant current in one or both plates, reducing the ensuing fluctuation-generated normal force while at the same time generating a lateral drag force. This hypothesis is confirmed by detailed numerical simulations as well as an analytical approach based on stochastic density functional theory.
Ostoma, T; Ostoma, Tom; Trushyk, Mike
1999-01-01
We propose experiments that might be set up to detect the increase in the velocity of light in a vacuum in the laboratory frame for photons travelling between (and perpendicular to) the Casimir plates in a vacuum. The Casimir plates are two closely spaced, conductive plates, where an attractive force is observed to exist between the plates called the 'Casimir Force'. We propose that the velocity of light in a vacuum increases when propagating between two transparent Casimir Plates. We call this effect the 'Light Velocity Casimir Effect' or LVC effect. The LVC effect happens because the vacuum energy density in between the plates is lower than that outside the Casimir plates. The conductive plates disallow certain frequencies of electrically charged virtual particles to exist inside the plates, thus lowering the inside vacuum particle density, compared to the density outside the plates. The reduced (electrically charged) virtual particle density results in fewer photon scattering events inside the plates, whic...
Casimir effect for a Cavity in the Spacetime with an Extra Dimension
Institute of Scientific and Technical Information of China (English)
CHENG Hong-Bo
2005-01-01
@@ We reexamine the Casimir effect for the rectangular cavity with two or three equal edges in the presence of compactified universal extra dimension. We derive the expressions for the Casimir energy and discuss the nature of Casimir force. We show analytically the extra-dimension corrections to the standard Casimir effect to put forward a new method of exploring the existence of extra dimensions of the Universe.
Finite temperature Casimir effect in Kaluza-Klein spacetime
Energy Technology Data Exchange (ETDEWEB)
Teo, L.P. [Faculty of Information Technology, Multimedia University, Jalan Multimedia, Cyberjaya, 63100 Selangor Darul Ehsan (Malaysia)], E-mail: lpteo@mmu.edu.my
2009-10-01
In this article, we consider the finite temperature Casimir effect in Kaluza-Klein spacetime due the vacuum fluctuation of massless scalar field with Dirichlet boundary conditions. We consider the general case where the extra dimensions (internal space) can be any compact connected manifold or orbifold without boundaries. Using piston analysis, we show that the Casimir force is always attractive at any temperature, regardless of the geometry of the internal space. Moreover, the magnitude of the Casimir force increases as the size of the internal space increases and it reduces to the Casimir force in (3+1)-dimensional Minkowski spacetime when the size of the internal space shrinks to zero. In the other extreme where the internal space is large, the Casimir force can increase beyond all bound. Asymptotic behaviors of the Casimir force in the low and high temperature regimes are derived and it is observed that the magnitude of the Casimir force grows linearly with temperature in the high temperature regime.
Graphene Casimir Interactions and Some Possible Applications
Phan, Anh D.
Scientific development requires profound understandings of micromechanical and nanomechanical systems (MEMS/NEMS) due to their applications not only in the technological world, but also for scientific understanding. At the micro- or nano-scale, when two objects are brought close together, the existence of stiction or adhesion is inevitable and plays an important role in the behavior operation of these systems. Such effects are due to surface dispersion forces, such as the van der Waals or Casimir interactions. The scientific understanding of these forces is particularly important for low-dimensional materials. In addition, the discovery of materials, such as graphitic systems has provided opportunities for new classes of devices and challenging fundamental problems. Therefore, investigations of the van der Waals or Caismir forces in graphene-based systems, in particular, and the solution generating non-touching systems are needed. In this study, the Casimir force involving 2D graphene is investigated under various conditions. The Casimir interaction is usually studied in the framework of the Lifshitz theory. According to this theory, it is essential to know the frequency-dependent reflection coefficients of materials. Here, it is found that the graphene reflection coefficients strongly depend on the optical conductivity of graphene, which is described by the Kubo formalism. When objects are placed in vacuum, the Casimir force is attractive and leads to adhesion on the surface. We find that the Casimir repulsion can be obtained by replacing vacuum with a suitable liquid. Our studies show that bromobenzene is the liquid providing this effect. We also find that this long-range force is temperature dependent and graphene/bromobenzene/metal substrate configuration can be used to demonstrate merely thermal Casimir interaction at room temperature and micrometer distances. These findings would provide good guidance and predictions for practical studies.
The Casimir effect: from quantum to critical fluctuations
Gambassi, Andrea
2008-01-01
The Casimir effect in quantum electrodynamics (QED) is perhaps the best-known example of fluctuation-induced long-ranged force acting on objects (conducting plates) immersed in a fluctuating medium (quantum electromagnetic field in vacuum). A similar effect emerges in statistical physics, where the force acting, e.g., on colloidal particles immersed in a binary liquid mixture is affected by the classical thermal fluctuations occurring in the surrounding medium. The resulting Casimir-like forc...
Klein-Gordon Equation with Casimir Potential for Attosecond Laser Pulse Interaction with Matter
Kozlovskii, Miroslaw P; Kozlowski, Miroslaw; Marciak-Kozlowska, Janina
2005-01-01
In this paper the Klein-Gordon equation (K-GE) is solved for the interaction of attosecond laser pulses with medium in which Casimir force operates. It is shown that for nanoscale structures, NEMS and MEMS, the attosecond laser pulses can be used as the tool for the investigation of the role played by Casimir force on the nanoscale. Key words: Casimir force; NEMS, MEMS, Attosecond laser pulses.
Finite-temperature Casimir effect in piston geometry and its classical limit
Energy Technology Data Exchange (ETDEWEB)
Lim, S.C. [Multimedia University, Faculty of Engineering, Cyberjaya, Selangor Darul Ehsan (Malaysia); Teo, L.P. [Multimedia University, Faculty of Information Technology, Cyberjaya, Selangor Darul Ehsan (Malaysia)
2009-03-15
We consider the Casimir force acting on a d-dimensional rectangular piston due to a massless scalar field with periodic, Dirichlet and Neumann boundary conditions and an electromagnetic field with perfect electric-conductor and perfect magnetic-conductor boundary conditions. The Casimir energy in a rectangular cavity is derived using the cut-off method. It is shown that the divergent part of the Casimir energy does not contribute to the Casimir force acting on the piston, thus renders an unambiguously defined Casimir force acting on the piston. At any temperature, it is found that the Casimir force acting on the piston increases from -{infinity} to 0 when the separation a between the piston and the opposite wall increases from 0 to {infinity}. This implies that the Casimir force is always an attractive force pulling the piston towards the closer wall, and the magnitude of the force gets larger as the separation a gets smaller. Explicit exact expressions for the Casimir force for small and large plate separations and for low and high temperatures are computed. The limits of the Casimir force acting on the piston when some pairs of transversal plates are large are also derived. An interesting result regarding the influence of temperature is that in contrast to the conventional result that the leading term of the Casimir force acting on a wall of a rectangular cavity at high temperature is the Stefan-Boltzmann (or black-body radiation) term which is of order T {sup d+1}, it is found that the contributions of this term from the two regions separating the piston cancel with each other in the case of piston. The high-temperature leading-order term of the Casimir force acting on the piston is of order T, which shows that the Casimir force has a nontrivial classical {Dirac_h}{yields}0 limit. Explicit formulas for the classical limit are computed. (orig.)
First-principles study of Casimir repulsion in metamaterials.
Yannopapas, Vassilios; Vitanov, Nikolay V
2009-09-18
We examine theoretically the Casimir effect between a metallic plate and several types of magnetic metamaterials in pursuit of Casimir repulsion, by employing a rigorous multiple-scattering theory for the Casimir effect. We first examine metamaterials in the form of two-dimensional lattices of inherently nonmagnetic spheres such as spheres made from materials possessing phonon-polariton and exciton-polariton resonances. Although such systems are magnetically active in infrared and optical regimes, the force between finite slabs of these materials and metallic slabs is plainly attractive since the effective electric permittivity is larger than the magnetic permeability for the studied spectrum. When lattices of magnetic spheres made from superparamagnetic composites are employed, we achieve not only Casimir repulsion but almost total suppression of the Casimir effect itself in the micrometer scale. PMID:19792414
Valchev, Galin; Dantchev, Daniel
2015-07-01
We study, using general scaling arguments and mean-field type calculations, the behavior of the critical Casimir force and its interplay with the van der Waals force acting between two parallel slabs separated at a distance L from each other, confining some fluctuating fluid medium, say a nonpolar one-component fluid or a binary liquid mixture. The surfaces of the slabs are coated by thin layers exerting strong preference to the liquid phase of the fluid, or one of the components of the mixture, modeled by strong adsorbing local surface potentials ensuring the so-called (+,+) boundary conditions. The slabs, on the other hand, influence the fluid by long-range competing dispersion potentials, which represent irrelevant interactions in renormalization-group sense. Under such conditions, one usually expects attractive Casimir force governed by universal scaling function, pertinent to the extraordinary surface universality class of Ising type systems, to which the dispersion potentials provide only corrections to scaling. We demonstrate, however, that below a given threshold thickness of the system Lcrit for a suitable set of slabs-fluid and fluid-fluid coupling parameters the competition between the effects due to the coatings and the slabs can result in sign change of the Casimir force acting between the surfaces confining the fluid when one changes the temperature T , the chemical potential of the fluid μ , or L . The last implies that by choosing specific materials for the slabs, coatings, and the fluid for L ≲Lcrit one can realize repulsive Casimir force with nonuniversal behavior which, upon increasing L , gradually turns into an attractive one described by a universal scaling function, depending only on the relevant scaling fields related to the temperature and the excess chemical potential, for L ≫Lcrit . We present arguments and relevant data for specific substances in support of the experimental feasibility of the predicted behavior of the force. It can
The covariant electromagnetic Casimir effect for real conducting spherical shells
Razmi, H
2016-01-01
Using the covariant electromagnetic Casimir effect (previously introduced for real conducting cylindrical shells [1]), the Casimir force experienced by a spherical shell, under Dirichlet boundary condition, is calculated. The renormalization procedure is based on the plasma cut-off frequency for real conductors. The real case of a gold (silver) sphere is considered and the corresponding electromagnetic Casimir force is computed. In the covariant approach, there isn't any decomposition of fields to TE and TM modes; thus, we do not need to consider the Neumann boundary condition in parallel to the Dirichlet problem and then add their corresponding results.
Casimir effect for two lossy dispersive dielectric slabs
Matloob, R.; Keshavarz, A.; Sedighi, D.
1999-11-01
The electromagnetic field is quantized using the Green's-function method for the geometry of a Fabry-Perot cavity, made up of two identical lossy dispersive slabs of finite thickness. The dielectric functions of the slabs are assumed to be an arbitrary complex function of frequency obeying causality requirements. The attractive Casimir force between the two slabs is calculated by the help of the latter field operators, via evaluating the difference between the vacuum pressures on both sides of each slab. Special attention is paid to the limiting case of the Casimir effect for two conducting plates. The Lorentz model of the dielectric function is used to demonstrate the variation of the force in terms of plasma frequency. The Casimir force expression is also related to the imaginary part of the response function. The latter expression is used to introduce the repulsive Casimir force between two conducting plates located inside a Fabry-Perot cavity.
Roberts, D. C.; Pomeau, Y.
2005-01-01
We calculate a force due to zero-temperature quantum fluctuations on a stationary object in a moving superfluid flow. We model the object by a localized potential varying only in the flow direction and model the flow by a three-dimensional weakly interacting Bose-Einstein condensate at zero temperature. We show that this force exists for any arbitrarily small flow velocity and discuss the implications for the stability of superfluid flow.
International Nuclear Information System (INIS)
As the technological advances lead to miniaturization of mechanical devices, engineers face new challenges that are brought about by the fundamentally different rules that apply at small scales. One of the biggest problems in small machines is the excessive wear of the many surfaces that work in contact with each other, which severely constrains the durability of such machine parts. Here, a force that is caused by the quantum fluctuations of electromagnetic field- known as the lateral Casimir force-is employed to propose a design for a potentially wear-proof rack and pinion with no contact, which can be miniaturized to nano-scale. We demonstrate that both uniform and harmonic lateral motion of the rack can be converted into unidirectional rotation of the pinion. The robustness of the design is studied by exploring the relation between the pinion velocity and the rack velocity in the different domains of the parameter space. The effects of friction and added external load are also examined
Casimir Effect at Finite Temperature in the Presence of One Fractal Extra Compactified Dimension
Institute of Scientific and Technical Information of China (English)
程红波
2012-01-01
We discuss the Casimir effect for massless scalar fields subject to the Diriehlet boundary conditions on the parallel plates at finite temperature in the presence of one fraetal extra eompactified dimension. We obtain the Casimir energy density with the help of the regularization of multiple zeta function with one arbitrary exponent and further the renormalized Casimir energy density involving the thermal corrections. It is found that when the temperature is sumciently high, the sign of the Casimir energy remains negative no matter how great the scale dimension 6 is within its allowed region. We derive and calculate the Casimir force between the parallel plates affected by the fractal additional compactified dimension and surrounding temperature. The stronger thermal influence leads the force to be stronger. The nature of the Casimir force keeps attractive.
An ``Anatomic approach" to study the Casimir effect
Intravaia, Francesco; Haakh, Harald; Henkel, Carsten
2010-03-01
The Casimir effect, in its simplest definition, is a quantum mechanical force between two objects placed in vacuum. In recent years the Casimir force has been the object of an exponentially growing attention both from theorists and experimentalists. A new generation of experiments paved the way for new challenges and spotted some shadows in the comparison to theory. Here we are going to isolate different contributions to the Casimir interaction and perform a detailed study to shine new light on this phenomenon. As an example, the contributions of Foucault (eddy current) modes will be discussed in different configurations. This ``anatomic approach'' allows to clearly put into evidence special features and to explain unusual behaviors. This brings new physical understanding on the undergoing physical mechanisms and suggests new ways to engineer the Casimir effect.
Casimir-Lifshitz interaction between dielectric heterostructures
International Nuclear Information System (INIS)
The interaction between arbitrary dielectric heterostructures is studied within the framework of a recently developed dielectric contrast perturbation theory. It is shown that periodically patterned dielectric or metallic structures lead to oscillatory lateral Casimir-Lifshitz forces, as well as modulations in the normal force as they are displaced with respect to one another. The strength of these oscillatory contributions increases with decreasing gap size and increasing contrast in the dielectric properties of the materials used in the heterostructures.
Casimir-Lifshitz interaction between dielectric heterostructures
Energy Technology Data Exchange (ETDEWEB)
Azari, Arash; Samanta, Himadri S; Golestanian, Ramin [Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH (United Kingdom)], E-mail: r.golestanian@sheffield.ac.uk
2009-09-15
The interaction between arbitrary dielectric heterostructures is studied within the framework of a recently developed dielectric contrast perturbation theory. It is shown that periodically patterned dielectric or metallic structures lead to oscillatory lateral Casimir-Lifshitz forces, as well as modulations in the normal force as they are displaced with respect to one another. The strength of these oscillatory contributions increases with decreasing gap size and increasing contrast in the dielectric properties of the materials used in the heterostructures.
Weak Gravitational Wave and Casimir Energy of a Scalar Field
Tavakoli, F.; Pirmoradian, R.; Parsabod, I.
2016-09-01
In this paper, we calculate the effect of a weak gravitational field on the Casimir force between two ideal plates subjected to a massless minimally coupled field. It is the aim of this work to study the Casimir energy under a weak perturbation of gravity. Moreover, the fluctuations of the stress-energy tensor for a scalar field in de Sitter space-time are computed as well.
Directory of Open Access Journals (Sweden)
Amir R. Askari
2014-01-01
Full Text Available The influence of the Casimir excitation on dynamic pull-in instability of a nanoelectromechanical beam under ramp-input voltage is studied. The ramp-input actuation has applications in frequency sweeping of RF-N/MEMS. The presented model is nonlinear due to the inherent nonlinearity of electrostatics and the Casimir excitations as well as the geometric nonlinearity of midplane stretching. A Galerkin based reduced order modeling is utilized. It is found that the calculated dynamic pull-in ramp input voltage leads to dynamic pull-in step input voltage by increasing the slope of voltage-time diagram. This fact is utilized to verify the results of present study.
Energy Technology Data Exchange (ETDEWEB)
Teo, L P [Faculty of Information Technology, Multimedia University, Jalan Multimedia, Cyberjaya, 63100, Selangor Darul Ehsan (Malaysia)], E-mail: lpteo@mmu.edu.my
2009-03-13
In this paper, the finite-temperature Casimir force acting on a two-dimensional Casimir piston due to an electromagnetic field is computed. It was found that if mixed boundary conditions are assumed on the piston and its opposite wall, then the Casimir force always tends to restore the piston toward the equilibrium position, regardless of the boundary conditions assumed on the walls transverse to the piston. In contrast, if pure boundary conditions are assumed on the piston and the opposite wall, then the Casimir force always tends to pull the piston toward the closer wall and away from the equilibrium position. The nature of the force is not affected by temperature. However, in the high-temperature regime, the magnitude of the Casimir force grows linearly with respect to temperature. This shows that the Casimir effect has a classical limit as has been observed in other literature.
The Casimir effect: From quantum to critical fluctuations
International Nuclear Information System (INIS)
The Casimir effect in quantum electrodynamics (QED) is perhaps the best-known example of fluctuation-induced long-ranged force acting on objects (conducting plates) immersed in a fluctuating medium (quantum electromagnetic field in vacuum). A similar effect emerges in statistical physics, where the force acting, e.g., on colloidal particles immersed in a binary liquid mixture is affected by the classical thermal fluctuations occurring in the surrounding medium. The resulting Casimir-like force acquires universal features upon approaching a critical point of the medium and becomes long-ranged at criticality. In turn, this universality allows one to investigate theoretically the temperature dependence of the force via representative models and to stringently test the corresponding predictions in experiments. In contrast to QED, the Casimir force resulting from critical fluctuations can be easily tuned with respect to strength and sign by surface treatments and temperature control. We present some recent advances in the theoretical study of the universal properties of the critical Casimir force arising in thin films. The corresponding predictions compare very well with the experimental results obtained for wetting layers of various fluids. We discuss how the Casimir force between a colloidal particle and a planar wall immersed in a binary liquid mixture has been measured with femto-Newton accuracy, comparing these experimental results with the corresponding theoretical predictions.
Casimir Effect of Scalar Massive Field
Mobassem, Sonia
2014-01-01
The energy momentum tensor is used to introduce the Casimir force of the massive scalar field acting on a nonpenetrating surface. This expression can be used to evaluate the vacuum force by employing the appropriate field operators. To simplify our formalism we also relates the vacuum force expression to the imaginary part of the Green function via the fluctuation dissipation theorem and Kubo formula. This allows one to evaluate the vacuum force without resorting to the process of field quantization. These two approaches are used to calculate the attractive force between two nonpenetrating plates. Special attention is paid to the generalization of the formalism to D + 1 space-time dimensions.
Fluctuations, dissipation and the dynamical Casimir effect
Dalvit, Diego A R; Mazzitelli, Francisco Diego
2010-01-01
Vacuum fluctuations provide a fundamental source of dissipation for systems coupled to quantum fields by radiation pressure. In the dynamical Casimir effect, accelerating neutral bodies in free space give rise to the emission of real photons while experiencing a damping force which plays the role of a radiation reaction force. Analog models where non-stationary conditions for the electromagnetic field simulate the presence of moving plates are currently under experimental investigation. A dissipative force might also appear in the case of uniform relative motion between two bodies, thus leading to a new kind of friction mechanism without mechanical contact. In this paper, we review recent advances on the dynamical Casimir and non-contact friction effects, highlighting their common physical origin.
Casimir effect in de Sitter spacetime
Saharian, A A
2011-01-01
The vacuum expectation value of the energy-momentum tensor and the Casimir forces are investigated for a massive scalar field with an arbitrary curvature coupling parameter in the geometry of two parallel plates, on the background of de Sitter spacetime. The field is prepared in the Bunch--Davies vacuum state and is constrained to satisfy Robin boundary conditions on the plates. The vacuum energy-momentum tensor is non-diagonal, with the off-diagonal component corresponding to the energy flux along the direction normal to the plates. It is shown that the curvature of the background spacetime decisively influences the behavior of the Casimir forces at separations larger than the curvature radius of de Sitter spacetime. In dependence of the curvature coupling parameter and the mass of the field, two different regimes are realized, which exhibit monotonic or oscillatory behavior of the forces. The decay of the Casimir force at large plate separation is shown to be power-law, with independence of the value of the...
Optical and Casimir effects in topological materials
Wilson, Justin H.
Two major electromagnetic phenomena, magneto-optical effects and the Casimir effect, have seen much theoretical and experimental use for many years. On the other hand, recently there has been an explosion of theoretical and experimental work on so-called topological materials, and a natural question to ask is how such electromagnetic phenomena change with these novel materials. Specifically, we will consider are topological insulators and Weyl semimetals. When Dirac electrons on the surface of a topological insulator are gapped or Weyl fermions in the bulk of a Weyl semimetal appear due to time-reversal symmetry breaking, there is a resulting quantum anomalous Hall effect (2D in one case and bulk 3D in the other, respectively). For topological insulators, we investigate the role of localized in-gap states which can leave their own fingerprints on the magneto-optics and can therefore be probed. We have shown that these states resonantly contribute to the Hall conductivity and are magneto-optically active. For Weyl semimetals we investigate the Casimir force and show that with thickness, chemical potential, and magnetic field, a repulsive and tunable Casimir force can be obtained. Additionally, various values of the parameters can give various combinations of traps and antitraps. We additionally probe the topological transition called a Lifshitz transition in the band structure of a material and show that in a Casimir experiment, one can observe a non-analytic "kink'' in the Casimir force across such a transition. The material we propose is a spin-orbit coupled semiconductor with large g-factor that can be magnetically tuned through such a transition. Additionally, we propose an experiment with a two-dimensional metal where weak localization is tuned with an applied field in order to definitively test the effect of diffusive electrons on the Casimir force---an issue that is surprisingly unresolved to this day. Lastly, we show how the time-continuous coherent state
Casimir Torque in Inhomogeneous Dielectric Plates
Long, William
2013-01-01
In this work, we consider a torque caused by the well known quantum mechanical Casimir effect arising from quantized field fluctuations between plates with inhomogeneous, sharply discontinuous, dielectric properties. While the Casimir effect is a relatively well understood phenomenon, systems resulting in lateral or rotational forces are far less developed; to our knowledge, a theoretical study of discontinuous dielectric variants of such systems has not been attempted. We utilize a Proximity Force Approximation in conjunction with the Lifshitz dielectric formula to perform theoretical analyses of resultant torques in systems with bisected and quadrisected dielectric regions. We also develop a high precision Monte Carlo type numerical integrator to approximate our derived expressions. Our calculations of an energy density linear with the alignment angle result in a constant torque and have implications in NEMS (nano electromechanical systems) and MEMS (micro electromechanical systems), including a postulated ...
International Nuclear Information System (INIS)
Using a previously formulated theory of quantum electrodynamics based on self-energy, we give a general method for computing the Lamb shift and related Casimir-Polder energies for a quantum system in the vicinity of perfectly conducting boundaries. Our results are exact and easily extendable to a full covariant relativistic form. As a particular example we apply the method to an atom near an infinite conducting plane, and we recover the standard QED results (which are known only in the dipole approximation) in a simple and straightforward manner. This is accomplished in the context of the new theory which is not second quantized and contains no vacuum fluctuations. (author)
Casimir repulsion between metallic objects in vacuum.
Levin, Michael; McCauley, Alexander P; Rodriguez, Alejandro W; Reid, M T Homer; Johnson, Steven G
2010-08-27
We give an example of a geometry in which two metallic objects in vacuum experience a repulsive Casimir force. The geometry consists of an elongated metal particle centered above a metal plate with a hole. We prove that this geometry has a repulsive regime using a symmetry argument and confirm it with numerical calculations for both perfect and realistic metals. The system does not support stable levitation, as the particle is unstable to displacements away from the symmetry axis. PMID:20868142
Exact solution for the Casimir stress in a spherically symmetric medium
Leonhardt, Ulf; Simpson, William M. R.
2011-10-01
We calculated the stress of the quantum vacuum, the Casimir stress, in a spherically symmetric medium, Maxwell’s fish eye, surrounded by a perfect mirror and derived an exact analytic solution. Our solution questions the idea that the Casimir force of a spherical mirror is repulsive—we found an attractive stress in the medium that diverges at the mirror.
The Casimir Effect at Finite Temperature in a Six-Dimensional Vortex Scenario
Cheng, Hongbo
2016-03-01
The Casimir effect for parallel plates satisfying the Dirichlet boundary condition in the context of effective QED coming from a six-dimensional Nielsen-Olesen vortex solution of the Abelian Higgs model with fermions coupled to gravity is studied at finite temperature. We find that the sign of the Casimir energy remains negative under the thermal influence. It is also shown that the Casimir force between plates will be weaker in the higher-temperature surroundings while keeps attractive. This Casimir effect involving the thermal influence is still inconsistent with the known experiments. We find that the thermal correction can not compensate or even reduce the modification from this kind of vortex model to make the Casimir force to be in less conflict with the measurements.
The Casimir effect at finite temperature in a six-dimensional vortex scenario
Cheng, Hongbo
2015-01-01
The Casimir effect for parallel plates satisfying the Dirichlet boundary condition in the context of effective QED coming from a six-dimensional Nielsen-Olesen vortex solution of the Abelian Higgs model with fermions coupled to gravity is studied at finite temperature. We find that the sign of the Casimir energy remains negative under the thermal influence. It is also shown that the Casimir force between plates will be weaker in the higher-temperature surroundings while keeps attractive. This Casimir effect involving the thermal influence is still inconsistent with the known experiments. We find that the thermal correction can not compensate or even reduce the modification from this kind of vortex model to make the Casimir force to be in less conflict with the measurements.
Enhancing Casimir repulsion via topological insulator multilayers
Zeng, Ran; Chen, Liang; Nie, Wenjie; Bi, Meihua; Yang, Yaping; Zhu, Shiyao
2016-08-01
We propose to observe the enhanced Casimir repulsion between two parallel multilayer walls made of alternating layers of a topological insulator (TI) and a normal insulator. Based on the transfer matrix method, the Fresnel coefficients matrix is generalized to apply to the TI multilayer structure. The Casimir repulsion under the influence of the magnetization orientation in the magnetic coatings on TI layer surfaces, the layer thicknesses, and the topological magnetoelectric polarizability, is investigated. We show that, for the multilayer structures with parallel magnetization on the TI layer surfaces, it is possible to enhance the repulsion by increasing the TI layer number, which is due to the accumulation of the contribution to the repulsion from the polarization rotation effect occurring on each TI layer surface. Generally, in the distance region where there is Casimir attraction between semi-infinite TIs, the force may turn into repulsion in TI multilayer structure, and in the region of repulsion for semi-infinite TI, the repulsive force can be enhanced in magnitude, the enhancement tends to a maximum while the structure contains sufficiently many layers.
Finite temperature Casimir effect in spacetime with extra compactified dimensions
Energy Technology Data Exchange (ETDEWEB)
Teo, L.P. [Faculty of Information Technology, Multimedia University, Jalan Multimedia, Cyberjaya 63100, Selangor Darul Ehsan (Malaysia)], E-mail: lpteo@mmu.edu.my
2009-02-16
In this Letter, we derive the explicit exact formulas for the finite temperature Casimir force acting on a pair of parallel plates in the presence of extra compactified dimensions within the framework of Kaluza-Klein theory. Using the piston analysis, we show that at any temperature, the Casimir force due to massless scalar field with Dirichlet boundary conditions on the plates is always attractive and the effect of extra dimensions becomes stronger when the size or number of the extra dimensions increases. These properties are not affected by the explicit geometry and topology of the Kaluza-Klein space.
Retardation turns the van der Waals attraction into a Casimir repulsion as close as 3 nm
Boström, Mathias; Sernelius, Bo; Brevik, Iver; Ninham, Barry W.
2012-01-01
Casimir forces between surfaces immersed in bromobenzene have recently been measured by Munday et al. [Nature (London) 454, 07610 (2009)]. Attractive Casimir forces were found between gold surfaces. The forces were repulsive between gold and silica surfaces. We show the repulsion is due to retardation effects. The van der Waals interaction is attractive at all separations. The retardation-driven repulsion sets in at around 3 nm. To our knowledge, retardation effects have never been found at s...
Casimir effect and radiative heat transfer between Chern Insulators
Rodriguez Lopez, Pablo; Grushin, Adolfo; Tse, Wang-Kong; Dalvit, Diego
2015-03-01
Chern Insulators are a class of two-dimensional topological materials. Their electronic properties are different from conventional materials, and lead to interesting new physics as quantum Hall effect in absence of an external magnetic field. Here we will review some of their special properties and, in particular, we will discuss the radiative heat transfer and the Casimir effect between two planar Chern Insulators sheets. Finally, we will see how to control the intensity and sign of this Casimir force and the requirements to observe a repulsive Casimir force in the lab with those materials. The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA Grant Agreement No. 302005.
Casimir Free Energy at High Temperatures: Grounded vs Isolated Conductors
Fosco, C D; Mazzitelli, F D
2016-01-01
We evaluate the difference between the Casimir free energies corresponding to either grounded or isolated perfect conductors, at high temperatures. We show that a general and simple expression for that difference can be given, in terms of the electrostatic capacitance matrix for the system of conductors. For the case of close conductors, we provide approximate expressions for that difference, by evaluating the capacitance matrix using the proximity force approximation. Since the high-temperature limit for the Casimir free energy for a medium described by a frequency-dependent conductivity diverging at zero frequency coincides with that of an isolated conductor, our results may shed light on the corrections to the Casimir force in the presence of real materials.
Some Developments of the Casimir Effect in $p$-Cavity of $(D+1)$-Dimensional Spacetime
Zhai, Xiang-Hua; Feng, Chao-Jun; Li, Xin-Zhou
2014-01-01
The Casimir effect for rectangular boxes has been studied for several decades. But there are still some points unclear. Recently, there are new developments related to this topic, including the demonstration of the equivalence of the regularization methods and the clarification of the ambiguity in the regularization of the temperature-dependent free energy. Also, the interesting quantum spring was raised stemming from the topological Casimir effect of the helix boundary conditions. We review these developments together with the general derivation of the Casimir energy of the $p$-dimensional cavity in ($D+1$)-dimensional spacetime, paying special attention to the sign of the Casimir force in a cavity with unequal edges. In addition, we also review the Casimir piston, which is a configuration related to rectangular cavity.
Casimir Piston of Real Materials and its Application to Multi-Layer Models
Teo, L P
2009-01-01
In this article, we derive the formula for the Casimir force acting on a piston made of real material moving inside a perfectly conducting rectangular box. It is shown that by taking suitable limits, one recovers the formula for the Casimir force acting on a perfectly conducting piston or an infinitely permeable piston. Lipshitz formula for finite temperature Casimir force acting on parallel plates made of real materials is re-derived by considering the five-layer model in the context of piston approach. It is observed that the divergences of the Casimir force will only cancel under certain conditions, for example, when the regions separated by the plates are filled with isorefractive media.
Geothermal Casimir phenomena for the sphere-plate and cylinder-plate configurations
Weber, Alexej; Gies, Holger
2010-01-01
We investigate the nontrivial interplay between geometry and temperature in the Casimir effect for the sphere-plate and cylinder-plate configurations. At low temperature, the thermal contribution to the Casimir force is dominated by this interplay, implying that standard approximation techniques such as the PFA are inapplicable even in the limit of small surface separation. Thermal fluctuations on scales of the thermal wavelength lead to a delocalization of the thermal force density at low te...
An experimental apparatus for measuring the Casimir effect at large distances
Energy Technology Data Exchange (ETDEWEB)
Antonini, P; Carugno, G; Messineo, G [INFN sez di Padova, via Marzolo 8, 35131 Padova (Italy); Bimonte, G [Dipartimento di Scienze Fisiche Universita di Napoli Federico II Complesso Universitario MSA, Via Cintia, 80126 Napoli, Italy and INFN, Sezione di Napoli, Napoli (Italy); Bressi, G [INFN sez. di Pavia, via Bassi 6, 27100 Pavia (Italy); Galeazzi, G [Dipartimento di Fisica, Universita di Padova, via Marzolo 8, 35131 Padova (Italy); Ruoso, G, E-mail: Giuseppe.Ruoso@lnl.infn.i [INFN Lab. Naz. Legnaro, viale dell' Universita 2, 35020 Legnaro (Italy)
2009-04-01
An experimental set-up for the measurement of the Casimir effect at separations larger than a few microns is presented. The apparatus is based on a mechanical resonator and uses a homodyne detection technique to sense the Casimir force in the plane-parallel configuration. First measurements in the 3-10 micrometer range show an unexpected large force probably due to patch effects.
Tunable Stable Levitation Based on Casimir Interaction between Nanostructures
Liu, Xianglei; Zhang, Zhuomin M.
2016-03-01
Quantum levitation enabled by repulsive Casimir force has been desirable due to the potential exciting applications in passive-suspension devices and frictionless bearings. In this paper, dynamically tunable stable levitation is theoretically demonstrated based on the configuration of dissimilar gratings separated by an intervening fluid using exact scattering theory. The levitation position is insensitive to temperature variations and can be actively tuned by adjusting the lateral displacement between the two gratings. This work investigates the possibility of applying quantum Casimir interactions into macroscopic mechanical devices working in a noncontact and low-friction environment for controlling the position or transducing lateral movement into vertical displacement at the nanoscale.
Finite Casimir Energies in Renormalizable Quantum Field Theory
Milton, K A
2004-01-01
Quantum vacuum energy has been known to have observable consequences since 1948 when Casimir calculated the force of attraction between parallel uncharged plates, a phenomenon confirmed experimentally with ever increasing precision. Casimir himself suggested that a similar attractive self-stress existed for a conducting spherical shell, but Boyer obtained a repulsive stress. Other geometries and higher dimensions have been considered over the years. Local effects, and divergences associated with surfaces and edges have been investigated by several authors. Quite recently, Graham et al. have re-examined such calculations, using conventional techniques of perturbative quantum field theory to remove divergences, and have suggested that previous self-stress results may be suspect. Here we show that most of the examples considered in their work are misleading; in particular, it is well-known that in two dimensions a circular boundary has a divergence in the Casimir energy for massless fields, while for general dim...
Geometry-Temperature Interplay in the Casimir Effect
Gies, Holger
2009-01-01
We discuss Casimir phenomena which are dominated by long-range fluctuations. A prime example is given by "geothermal" Casimir phenomena where thermal fluctuations in open Casimir geometries can induce significantly enhanced thermal corrections. We illustrate the underlying mechanism with the aid of the inclined-plates configuration, giving rise to enhanced power-law temperature dependences compared to the parallel-plates case. In limiting cases, we find numerical evidence even for fractional power laws induced by long-range fluctuations. We demonstrate that thermal energy densities for open geometries are typically distributed over length scales of 1/T. As an important consequence, approximation methods for thermal corrections based on local energy-density estimates such as the proximity-force approximation are expected to become unreliable even at small surface separations.
Electromagnetic normal modes and Casimir effects in layered structures
Sernelius, Bo E
2014-01-01
We derive a general procedure for finding the electromagnetic normal modes in layered structures. We apply this procedure to planar, spherical and cylindrical structures. These normal modes are important in a variety of applications. They are the only input needed in calculations of Casimir interactions. We present explicit expression for the condition for modes and Casimir energy for a large number of specific geometries. The layers are allowed to be two-dimensional so graphene and graphene-like sheets as well as two-dimensional electron gases can be handled within the formalism. Also forces on atoms in layered structures are obtained. One side-result is the van der Waals and Casimir-Polder interaction between two atoms.
Calculating Casimir Energies in Renormalizable Quantum Field Theory
Milton, K A
2003-01-01
Quantum vacuum energy has been known to have observable consequences since 1948 when Casimir calculated the force of attraction between parallel uncharged plates, a phenomenon confirmed experimentally with ever increasing precision. Casimir himself suggested that a similar attractive self-stress existed for a conducting spherical shell, but Boyer obtained a repulsive stress. Other geometries and higher dimensions have been considered over the years. Local effects, and divergences associated with surfaces and edges have been considered by several authors. Quite recently, Graham et al. have re-examined such calculations, using conventional techniques of perturbative quantum field theory to remove divergences, and have suggested that previous self-stress results may be suspect. Here we show that the examples considered in their work are misleading; in particular, it is well-known that in two dimensions a circular boundary has a divergence in the Casimir energy for massless fields, while for general dimension $D$...
Interplay between geometry and temperature in the Casimir effect
Energy Technology Data Exchange (ETDEWEB)
Weber, Alexej
2010-06-23
In this thesis, we investigate the interplay between geometry and temperature in the Casimir effect for the inclined-plates, sphere-plate and cylinder-plate configurations. We use the worldline approach, which combines the string-inspired quantum field theoretical formalism with Monte Carlo techniques. The approach allows the precise computation of Casimir energies in arbitrary geometries. We analyze the dependence of the Casimir energy, force and torque on the separation parameter and temperature T, and find Casimir phenomena which are dominated by long-range fluctuations. We demonstrate that for open geometries, thermal energy densities are typically distributed on scales of thermal wavelengths. As an important consequence, approximation methods for thermal corrections based on local energy-density estimates, such as the proximity-force approximation, are found to become unreliable even at small surface-separations. Whereas the hightemperature behavior is always found to be linear in T, richer power-law behaviors at small temperatures emerge. In particular, thermal forces can develop a non-monotonic behavior. Many novel numerical as well as analytical results are presented. (orig.)
Critical Casimir effect in three-dimensional Ising systems: Measurements on binary wetting films
International Nuclear Information System (INIS)
The critical Casimir force (CF) is observed in thin wetting films of a binary liquid mixture close to the liquid/vapor coexistence. X-ray reflectivity shows thickness (L) enhancement near the bulk consolute point. The extracted Casimir amplitude Δ+-=3±1 agrees with the theoretical universal value for the antisymmetric 3D Ising films. The onset of CF in the one-phase region occurs at L/ξ∼5 regardless of whether the bulk correlation length ξ is varied with temperature or composition. The shape of the Casimir scaling function depends monotonically on the dimensionality
Dowker, J S
2011-01-01
A piston is introduced into a spherical lune Casimir cavity turning it into two adjacent lunes separated by the (hemispherical) piston. On the basis of zeta function regularisation, the vacuum energy of the arrangement is finite for conformal propagation in space-time. For even spheres this energy is independent of the angle of the lune. For odd dimensions it is shown that for all Neumann, or all Dirichlet, boundary conditions the piston is attracted or repelled by the nearest wall if d=3,7,... or if d=1,5,..., respectively. For hybrid N-D conditions these requirements are switched. If a mass is added, divergences arise which render the model suspect. The analysis, however, is relatively straightforward and involves the Barnes zeta function.
Casimir rack and pinion as a miniaturized kinetic energy harvester.
Miri, MirFaez; Etesami, Zahra
2016-08-01
We study a nanoscale machine composed of a rack and a pinion with no contact, but intermeshed via the lateral Casimir force. We adopt a simple model for the random velocity of the rack subject to external random forces, namely, a dichotomous noise with zero mean value. We show that the pinion, even when it experiences random thermal torque, can do work against a load. The device thus converts the kinetic energy of the random motions of the rack into useful work.
Casimir rack and pinion as a miniaturized kinetic energy harvester
Miri, MirFaez; Etesami, Zahra
2016-08-01
We study a nanoscale machine composed of a rack and a pinion with no contact, but intermeshed via the lateral Casimir force. We adopt a simple model for the random velocity of the rack subject to external random forces, namely, a dichotomous noise with zero mean value. We show that the pinion, even when it experiences random thermal torque, can do work against a load. The device thus converts the kinetic energy of the random motions of the rack into useful work.
Critical Casimir interactions between Janus particles.
Labbé-Laurent, M; Dietrich, S
2016-08-21
Recently there has been strong experimental and theoretical interest in studying the self-assembly and the phase behavior of patchy and Janus particles, which form colloidal suspensions. Although in this quest a variety of effective interactions have been proposed and used in order to achieve a directed assembly, the critical Casimir effect stands out as being particularly suitable in this respect because it provides both attractive and repulsive interactions as well as the potential of a sensitive temperature control of their strength. Specifically, we have calculated the critical Casimir force between a single Janus particle and a laterally homogeneous substrate as well as a substrate with a chemical step. We have used the Derjaguin approximation and compared it with results from full mean field theory. A modification of the Derjaguin approximation turns out to be generally reliable. Based on this approach we have derived the effective force and the effective potential between two Janus cylinders as well as between two Janus spheres. PMID:27444691
Casimir energy in a spherical surface within surface impedance approach: The Drude model
Rosa, Luigi; Trozzo, Lucia
2016-09-01
The Casimir Energy of a spherical cavity whose surface is characterized by means of its surface impedance is calculated. The material properties of the boundary are described by means of the Drude model, so that a generalization of a previous result, based on plasma model, is obtained. The limits of the proposed approach are analyzed and a possible solution is suggested. The possibility of modulating the sign of the Casimir force from positive (repulsion) to negative (attraction) is studied.
Negative Entropies in Casimir and Casimir-Polder Interactions
Milton, Kimball A; Kalauni, Pushpa; Parashar, Prachi; Guérout, Romain; Ingold, Gert-Ludwig; Lambrecht, Astrid; Reynaud, Serge
2016-01-01
It has been increasingly becoming clear that Casimir and Casimir-Polder entropies may be negative in certain regions of temperature and separation. In fact, the occurrence of negative entropy seems to be a nearly ubiquitous phenomenon. This is most highlighted in the quantum vacuum interaction of a nanoparticle with a conducting plate or between two nanoparticles. It has been argued that this phenomenon does not violate physical intuition, since the total entropy, including the self-entropies of the plate and the nanoparticle, should be positive. New calculations, in fact, seem to bear this out at least in certain cases.
A Generalization of Electromagnetic Fluctuation-Induced Casimir Energy
Directory of Open Access Journals (Sweden)
Yi Zheng
2015-01-01
Full Text Available Intermolecular forces responsible for adhesion and cohesion can be classified according to their origins; interactions between charges, ions, random dipole—random dipole (Keesom, random dipole—induced dipole (Debye are due to electrostatic effects; covalent bonding, London dispersion forces between fluctuating dipoles, and Lewis acid-base interactions are due to quantum mechanical effects; pressure and osmotic forces are of entropic origin. Of all these interactions, the London dispersion interaction is universal and exists between all types of atoms as well as macroscopic objects. The dispersion force between macroscopic objects is called Casimir/van der Waals force. It results from alteration of the quantum and thermal fluctuations of the electrodynamic field due to the presence of interfaces and plays a significant role in the interaction between macroscopic objects at micrometer and nanometer length scales. This paper discusses how fluctuational electrodynamics can be used to determine the Casimir energy/pressure between planar multilayer objects. Though it is confirmation of the famous work of Dzyaloshinskii, Lifshitz, and Pitaevskii (DLP, we have solved the problem without having to use methods from quantum field theory that DLP resorted to. Because of this new approach, we have been able to clarify the contributions of propagating and evanescent waves to Casimir energy/pressure in dissipative media.
Energy Technology Data Exchange (ETDEWEB)
Dowker, J S, E-mail: dowker@man.ac.uk [Theory Group, School of Physics and Astronomy, University of Manchester, Manchester (United Kingdom)
2011-08-07
A piston is introduced into a spherical lune Casimir cavity turning it into two adjacent lunes separated by the (hemispherical) piston. On the basis of zeta-function regularization, the vacuum energy of the arrangement is finite for conformal propagation in spacetime. For even spheres this energy is independent of the angle of the lune. For odd dimensions it is shown that for all Neumann, or all Dirichlet, boundary conditions the piston is repelled or attracted by the nearest wall if d = 3, 7, ... or if d = 1, 5, ... , respectively. For hybrid N-D conditions these requirements are switched. If a mass is added, divergences arise which render the model suspect. The analysis, however, is relatively straightforward and involves the Barnes zeta function. The extension to finite temperatures is made and it is shown that for the 3, 7, ... series of odd spheres, the repulsion by the walls continues but that, above a certain temperature, the free energy acquires two minima symmetrically placed about the midpoint.
Casimir Effect Under Quasi-Periodic Boundary Condition Inspired by Nanotubes
Feng, Chao-Jun; Li, Xin-Zhou; Zhai, Xiang-Hua
2014-01-01
When one studies the Casimir effect, the periodic (anti-periodic) boundary condition is usually taken to mimic a periodic (anti-periodic) structure for a scalar field living in a flat space with a non-Euclidean topology. However, there could be an arbitrary phase difference between the value of the scalar field on one endpoint of the unit structure and that on the other endpoint, such as the structure of nanotubes. Then, in this paper, a periodic condition on the ends of the system with an additional phase factor, which is called the "quasi-periodic" condition, is imposed to investigate the corresponding Casimir effect. And an attractive or repulsive Casimir force is found, whose properties depend on the phase angle value. Especially, the Casimir effect disappears when the phase angle takes a particular value. High dimensional spacetime case is also investigated.
Proposal for a Casimir-driven parametric amplifier
Imboden, M; Campbell, D K; Bishop, D J
2014-01-01
In this paper, we discuss a design for a MEMS parametric amplifier modulated by the Casimir force. We present the theory for such a device and show that it allows for the implementation of a very sensitive voltage measuring technique, where the amplitude of a high quality factor resonator includes a tenth power dependency on an applied DC voltage. This approach opens up a new and powerful measuring modality, applicable to other measurement types.
Casimir effects in atomic, molecular, and optical physics
Babb, James F
2010-01-01
The long-range interaction between two atoms and the long-range interaction between an ion and an electron are compared at small and large intersystem separations. The vacuum dressed atom formalism is applied and found to provide a framework for interpretation of the similarities between the two cases. The van der Waals forces or Casimir-Polder potentials are used to obtain insight into relativistic and higher multipolar terms.
Direct Measurement of intermediate-range Casimir-Polder potentials
Bender, Helmar; Marzok, Carsten; Zimmermann, Claus; Slama, Sebastian
2009-01-01
We present the first direct measurements of Casimir-Polder forces between solid surfaces and atomic gases in the transition regime between the electrostatic short-distance and the retarded long-distance limit. The experimental method is based on ultracold ground-state Rb atoms that are reflected from evanescent wave barriers at the surface of a dielectric glass prism. Our novel approach does not require assumptions about the potential shape. The experimental data confirm the theoretical prediction in the transition regime.
Retardation turns the van der Waals attraction into Casimir repulsion already at 3 nm
Boström, Mathias; Brevik, Iver; Ninham, Barry W
2012-01-01
Casimir forces between surfaces immersed in bromobenzene have recently been measured by Munday et al. Attractive Casimir forces were found between gold surfaces. The forces were repulsive between gold and silica surfaces. We show the repulsion is due to retardation effects. The van der Waals interaction is attractive at all separations. The retardation driven repulsion sets in already at around 3 nm. To our knowledge retardation effects have never been found at such a small distance before. Retardation effects are usually associated with large distances.
The Casimir effect for fields with arbitrary spin
Energy Technology Data Exchange (ETDEWEB)
Stokes, Adam; Bennett, Robert, E-mail: r.bennett@leeds.ac.uk
2015-09-15
The Casimir force arises when a quantum field is confined between objects that apply boundary conditions to it. In a recent paper we used the two-spinor calculus to derive boundary conditions applicable to fields with arbitrary spin in the presence of perfectly reflecting surfaces. Here we use these general boundary conditions to investigate the Casimir force between two parallel perfectly reflecting plates for fields up to spin-2. We use the two-spinor calculus formalism to present a unified calculation of well-known results for spin-1/2 (Dirac) and spin-1 (Maxwell) fields. We then use our unified framework to derive new results for the spin-3/2 and spin-2 fields, which turn out to be the same as those for spin-1/2 and spin-1. This is part of a broader conclusion that there are only two different Casimir forces for perfectly reflecting plates—one associated with fermions and the other with bosons.
Effect of the heterogeneity of metamaterials on the Casimir-Lifshitz interaction
International Nuclear Information System (INIS)
The Casimir-Lifshitz interaction between metamaterials is studied using a model that takes into account the structural heterogeneity of the dielectric and magnetic properties of the bodies. A recently developed perturbation theory for the Casimir-Lifshitz interaction between arbitrary material bodies is generalized to include nonuniform magnetic permeability profiles and used to study the interaction between the magneto-dielectric heterostructures within the leading order. The metamaterials are modeled as two-dimensional arrays of domains with varying permittivity and permeability. In the case of two semi-infinite bodies with flat boundaries, the patterned structure of the material properties is found to cause the normal Casimir-Lifshitz force to develop an oscillatory behavior when the distance between the two bodies is comparable to the wavelength of the patterned features in the metamaterials. The nonuniformity also leads to the emergence of lateral Casimir-Lifshitz forces, which tend to strengthen as the gap size becomes smaller. Our results suggest that the recent studies on Casimir-Lifshitz forces between metamaterials, which have been performed with the aim of examining the possibility of observing the repulsive force, should be revisited to include the effect of the patterned structure at the wavelength of several hundred nanometers that coincides with the relevant gap size in the experiments.
Schwinger's Dynamical Casimir Effect: Bulk Energy Contribution
Carlson, Carl E.; Molina--Paris, Carmen; Perez--Mercader, Juan; Visser, Matt(School of Mathematics, Statistics, and Operations Research, Victoria University of Wellington, PO Box 600, Wellington, 6140, New Zealand)
1996-01-01
Schwinger's Dynamical Casimir Effect is one of several candidate explanations for sonoluminescence. Recently, several papers have claimed that Schwinger's estimate of the Casimir energy involved is grossly inaccurate. In this letter, we show that these calculations omit the crucial volume term. When the missing term is correctly included one finds full agreement with Schwinger's result for the Dynamical Casimir Effect. We have nothing new to say about sonoluminescence itself except to affirm ...
The electromagnetic Casimir effect of spherical cavity
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
The Casimir effect results from the zero-point energy of vacuum. A spherical cavity can be divided into three regions, and we make an analysis of every region and then give a formal solution of Casimir energy. The zeta-function regularization is also used to dispel the divergence of the summation. At the end, we can see the Casimir effect of a single sphere is included in our results.
Casimir interaction between a plate and a cylinder
Emig, T.; Jaffe, R. L.; Kardar, M.; Scardicchio, A.
2006-01-01
We find the exact Casimir force between a plate and a cylinder, a geometry intermediate between parallel plates, where the force is known exactly, and the plate--sphere, where it is known at large separations. The force has an unexpectedly weak decay \\sim L/(H^3 \\ln(H/R)) at large plate--cylinder separations H (L and R are the cylinder length and radius), due to transverse magnetic modes. Path integral quantization with a partial wave expansion additionally gives a qualitative difference for ...
Geothermal Casimir phenomena for the sphere-plate and cylinder-plate configurations
Weber, Alexej
2010-01-01
We investigate the nontrivial interplay between geometry and temperature in the Casimir effect for the sphere-plate and cylinder-plate configurations. At low temperature, the thermal contribution to the Casimir force is dominated by this interplay, implying that standard approximation techniques such as the PFA are inapplicable even in the limit of small surface separation. Thermal fluctuations on scales of the thermal wavelength lead to a delocalization of the thermal force density at low temperatures. As a consequence, the temperature dependence strongly differs from naive expectations. Most prominently, thermal forces can develop non-monotonic behavior below a critical temperature. We perform a comprehensive study of such geothermal phenomena in these Casimir geometries, using analytical and numerical worldline techniques for Dirichlet scalar fluctuations.
2015-01-01
The objective of the meeting is to promote contacts between scientists working in the field of Relativity, Gravitation and Cosmology and related fields. It is well known that the important role in Gravitation and Cosmology is played by the Casimir effect. To underline this, special Satellite Symposia devoted to this effect have been included in the Programs of the 7th and 8th Friedmann Seminars. The Casimir effect is a multidisciplinary subject. Its applications extend from gravitation and cosmology to the van der Waals forces, materials properties and nanotechnology. All these subjects are traditionally touched at the Satellite Simposia on the Casimir effect.
Supersymmetry Breaking Casimir Warp Drive
Obousy, Richard K.
2005-01-01
Within the framework of brane-world models it is possible to account for the cosmological constant by assuming supersymmetry is broken on the 3-brane but preserved in the bulk. An effective Casimir energy is induced on the brane due to the boundary conditions imposed on the compactified extra dimensions. It will be demonstrated that modification of these boundary conditions allows a spacecraft to travel at any desired speed due to a local adjustment of the cosmological constant which effectiv...
Casimir rack and pinion as a miniaturized kinetic energy harvester.
Miri, MirFaez; Etesami, Zahra
2016-08-01
We study a nanoscale machine composed of a rack and a pinion with no contact, but intermeshed via the lateral Casimir force. We adopt a simple model for the random velocity of the rack subject to external random forces, namely, a dichotomous noise with zero mean value. We show that the pinion, even when it experiences random thermal torque, can do work against a load. The device thus converts the kinetic energy of the random motions of the rack into useful work. PMID:27627286
Energy Technology Data Exchange (ETDEWEB)
Grueneberg, Daniel
2008-02-15
To study how the behavior of the thermodynamic Casimir force changes qualitatively and quantitatively due to the presence of such interactions - compared to systems with purely short-range interactions - is the aim of this work. Considering d-dimensional models belonging to the universality class of the O(n)-symmetrical systems, the thermodynamic Casimir force and its leading corrections are derived for temperatures at and above the transition temperature (T{>=}T{sub c,{infinity}}). The underlying pair potential is assumed to be isotropic and long-ranged, decaying asymptotically proportional to x{sup -(d+{sigma}}{sup )} for large separations x, where the value of the parameter {sigma} is restricted to the interval 2<{sigma}<4. By solving an appropriate spherical model in 2
Self-similar plates: Casimir energies
Shajesh, K V; Cavero-Peláez, Inés; Parashar, Prachi
2016-01-01
We construct various self-similar configurations using parallel $\\delta$-function plates and show that it is possible to evaluate the Casimir interaction energy of these configurations using the idea of self-similarity alone. We restrict our analysis to interactions mediated by a scalar field, but the extension to electromagnetic field is immediate. Our work unveils an easy and powerful method that can be easily employed to calculate the Casimir energies of a class of self-similar configurations. As a highlight, in an example, we determine the Casimir interaction energy of a stack of parallel plates constructed by positioning $\\delta$-function plates at the points constituting the Cantor set, a prototype of a fractal. This, to our knowledge, is the first time that the Casimir energy of a fractal configuration has been reported. Remarkably, the Casimir energy of some of the configurations we consider turn out to be positive, and a few even have zero Casimir energy. For the case of positive Casimir energy that ...
The holographic supersymmetric Casimir energy
Genolini, Pietro Benetti; Martelli, Dario; Sparks, James
2016-01-01
We consider a general class of asymptotically locally AdS_5 solutions of minimal gauged supergravity, that are dual to superconformal field theories on curved backgrounds S^1 x M_3 preserving two supercharges. We demonstrate that standard holographic renormalization corresponds to a scheme that breaks supersymmetry. We propose new boundary terms that restore supersymmetry, and show that for smooth solutions with topology S^1 x R^4 the improved on-shell action reproduces both the supersymmetric Casimir energy and the field theory BPS relation between charges.
Supersymmetry Breaking Casimir Warp Drive
Obousy, R K
2005-01-01
Within the framework of brane-world models it is possible to account for the cosmological constant by assuming supersymmetry is broken on the 3-brane but preserved in the bulk. An effective Casimir energy is induced on the brane due to the boundary conditions imposed on the compactified extra dimensions. It will be demonstrated that modification of these boundary conditions allows a spacecraft to travel at any desired speed due to a local adjustment of the cosmological constant which effectively contracts/expands space-time in the front/rear of the ship resulting in motion potentially faster than the speed of light as seen by observers outside the disturbance.
Supersymmetry Breaking Casimir Warp Drive
International Nuclear Information System (INIS)
This paper utilizes a recent model which relates the cosmological constant to the Casimir energy of the extra dimensions in brane-world theories. The objective of this paper is to demonstrate that, given some sufficiently advanced civilization with the ability to manipulate the radius of the extra dimension, a local adjustment of the cosmological constant could be created. This adjustment would facilitate an expansion/contraction of the spacetime around a spacecraft creating an exotic form of field-propulsion. This idea is analogous to the Alcubierre bubble, but differs entirely in the approach, utilizing the physics of higher dimensional quantum field theory, instead of general relativity
Derivative expansion for the Casimir effect at zero and finite temperature in $d+1$ dimensions
Fosco, C D; Mazzitelli, F D
2012-01-01
We apply the derivative expansion approach to the Casimir effect for a real scalar field in $d$ spatial dimensions, to calculate the next to leading order term in that expansion, namely, the first correction to the proximity force approximation. The field satisfies either Dirichlet or Neumann boundary conditions on two static mirrors, one of them flat and the other gently curved. We show that, for Dirichlet boundary conditions, the next to leading order term in the Casimir energy is of quadratic order in derivatives, regardless of the number of dimensions. Therefore it is local, and determined by a single coefficient. We show that the same holds true, if $d \
Thermo-field Dynamics of the Casimir Effect and Its Quantum Deformation
Institute of Scientific and Technical Information of China (English)
景辉; 解炳昊; 陈景灵
2001-01-01
The Casimir effect of the deformed cavity field at finite temperature is investigated by generalizing the thermofield dynamics formalism into a q-deformed version. It has been shown that the impact of q-deformation on theCasimir force only manifests in the finite-temperature case and the expression for the ideal pure vacuum remainsunchanged, which almost coincides with the suggestions of Man'ko et al. [Phys. Lett. A 176(1993)173] aboutthe nature of q-oscillators as the nonlinear vibrations of electromagnetic field.
Finite-temperature Casimir effect in the presence of nonlinear dielectrics
DEFF Research Database (Denmark)
Kheirandish, Fardin; Amooghorban, Ehsan; Soltani, Morteza
2011-01-01
Starting from a Lagrangian, the electromagnetic field in the presence of a nonlinear dielectric medium is quantized using path-integral techniques, and correlation functions of different fields are calculated. The susceptibilities of the nonlinear medium are obtained, and their relations to...... coupling functions are determined. Finally, the Casimir energy and force in the presence of a nonlinear medium at finite temperature are calculated....
L'effet Casimir : théorie et expériences
Lambrecht, A.; Genet, C.; Intravaia, F.; Reynaud, S.
2004-11-01
L'existence de fluctuations irréductibles de champ dans le vide est une prédiction importante de la théorie quantique. Ces fluctuations ont de nombreuses conséquences observables comme l'effet Casimir, qui est maintenant mesuré avec une bonne précision et un bon accord avec la théorie, pourvu que celle-ci tienne compte des différences entre les expériences rélles et la situation idéale considérée par H.G.B. Casimir. Nous présenterons quelqu'unes des expériences récentes et discuterons les principales corrections à la force de Casimir liées à la situation expérimentale.
Inhomogeneity-related cutoff dependence of the Casimir energy and stress
Bao, F; Fang, M; He, S
2015-01-01
The cutoff dependence of the Casimir energy and stress is studied using the Green's function method for a system that is piecewise-smoothly inhomogeneous along one dimension. The asymptotic cylinder kernel expansions of the energy and stress are obtained, with some extra cutoff terms that are induced by the inhomogeneity. Introducing interfaces to the system one by one shows how those cutoff terms emerge and illuminates their physical interpretations. Based on that, we propose a subtraction scheme to address the problem of the remaining cutoff dependence in the Casimir stress in an inhomogeneous medium, and show that the nontouching Casimir force between two separated bodies is cutoff independent. The cancellation of the electric and magnetic contributions to the surface divergence near a perfectly conducting wall is found to be incomplete in the case of inhomogeneity.
Determination of the Contact Angle Based on the Casimir Effect
Mazuruk, K.; Volz, M. P.
2015-01-01
In several crystal growth processed based on capillarity, a melt comes into contact with a crucible wall at an angle defined as the contact angle. For molten metals and semiconductors, this contact angle is dependent upon both the crucible and melt material and typical values fall in the range 80-170deg. However, on a microscopic scale, there does not exist a precise and sharp contact angle but rather the melt and solid surfaces merge smoothly and continuously over a distance of up to several micrometers. Accurate modeling requires a more advanced treatment of this interaction. The interaction between the melt and solid surfaces can be calculated by considering two forces: a short-range repulsive force and a longer range (up to a few micrometers) Casimir force. The Casimir force between the two bodies of complex geometry is calculated using a retarded temperature Green's function (Matsubara type) for the photon in the medium. The governing equations are cast in the form of a set of boundary integral equations which are then solved numerically for the case of molten Ge on SiO2. The shape of the molten surface approaching the flat solid body is determined, and the contact angle is defined as the angle between the two surfaces at the microscopically asymptotic distance of 1-2 micrometers. The formulation of this model and the results of the numerical calculations will be presented and discussed.
PREFACE: International Workshop '60 Years of the Casimir Effect'
Barton, Gabriel; Carugno, Giovanni; Dodonov, Victor; Man'ko, Margarita
2009-07-01
In 1948 Hendrick Casimir published a short article predicting that (neutral) ideal metallic plates attract each other. This attraction is widely ascribed to the quantum vacuum fluctuations of the electromagnetic field (even though away from the limit of ideal metals it depends demonstrably on the physics of the charge carriers vanishing when they cease to carry). Casimir's remarkable discovery, nowadays called the Casimir effect, has charmed several generations of physicists. In the last decade alone, more than a thousand publications have addressed its many consequences, generalizations, and possible applications in different areas from particle physics to cosmology. Interest in the field is still growing driven by impressive progress in experimental skills and its importance for the recently opened-up area of micro- and nano-electromechanical systems: according to the Thompson ISI Web of Science database, in 2005 the number of papers related to the Casimir effect or to Casimir forces jumped to over 125, compared to approximately 60 in 2000 and 30 in 1995. The increase continues, with more than 170 papers in 2008. The International Workshop '60 Years of the Casimir Effect' took place on 23-27June 2008, in Brasilia (Brazil) organized by the International Center for Condensed Matter Physics (ICCMP). The purpose was to celebrate this anniversary of Casimir's pioneering paper by inviting the leading specialists in the area, both theorists and experimentalists, together with young researchers and post-graduate students interested in hearing about the most recent achievements in the field. The Workshop was attended by 65 participants from 14 countries, who presented 41 talks and 12 posters. These Proceedings contain extended versions of almost all the talks and some posters, plus several papers by authors who had planned to attend but for various reasons could not. The contributions are divided (with some inevitable arbitrariness) into four groups. The largest one
Casimir Effect, Hawking Radiation and Trace Anomaly
Setare, M R
2001-01-01
The Casimir energy for massless scalar field of two parallel conductor, in two dimensional Schwarzchild black hole background, with Dirichlet boundary conditions is calculated by making use of general properties of renormalized stress tensor. We show that vacuum expectation value of stress tensor can be obtain by Casimir effect, trace anomaly and Hawking radiation. Four-dimensional of this problem, by this method, is under progress by this author.
Curved Casimir Operators and the BGG Machinery
Andreas Cap; Vladimír Soucek
2007-01-01
We prove that the Casimir operator acting on sections of a homogeneous vector bundle over a generalized flag manifold naturally extends to an invariant differential operator on arbitrary parabolic geometries. We study some properties of the resulting invariant operators and compute their action on various special types of natural bundles. As a first application, we give a very general construction of splitting operators for parabolic geometries. Then we discuss the curved Casimir operators on...
Casimir effect for curved boundaries in Robertson-Walker spacetime
Energy Technology Data Exchange (ETDEWEB)
Saharian, A A [Department of Physics, Yerevan State University, 1 Alex Manoogian Street, 0025 Yerevan (Armenia); Setare, M R, E-mail: saharian@ysu.a, E-mail: rezakord@ipm.i [Department of Science, Payame Noor University, Bijar (Iran, Islamic Republic of)
2010-11-21
Vacuum expectation values of the energy-momentum tensor and the Casimir forces are evaluated for scalar and electromagnetic fields in the geometry of two curved boundaries on the background of the Robertson-Walker spacetime with negative spatial curvature. The boundaries under consideration are conformal images of the flat boundaries in Rindler spacetime. Robin boundary conditions are imposed in the case of the scalar field and perfect conductor boundary conditions are assumed for the electromagnetic field. We use the conformal relation between the Robertson-Walker and Rindler spacetimes and the corresponding results for two parallel plates moving with uniform proper acceleration through the Fulling-Rindler vacuum. For the general scale factor the vacuum energy-momentum tensor is decomposed into the boundary-free and boundary-induced parts. The latter is non-diagonal. The Casimir forces are directed along the normals to the boundaries. For the Dirichlet and Neumann scalars and for the electromagnetic field these forces are attractive for all separations.
Directory of Open Access Journals (Sweden)
LIN Ruihui
2014-02-01
Full Text Available We reconsider the thermal scalar Casimir effect for p-dimensional hypercubic cavity inside D+1-dimensional Minkowski space-time.The thermal Casimir free energy can be divided into the divergent zero-temperature part and the automatically finite temperature-dependent part through standard quantum field theory treatments.Due to the finiteness,the regularization of the temperature-dependent part,which is also required for the convergency of the Casimir energy and the vanishing of the Casimir force with the separation increasing to infinity,is neglected in some literatures.We derive rigorously the regularization of the zero temperature part as well as the temperature-dependent part of the free energy by making use of the zeta function technique and the Abel-Plana formula.In the cases of D=3,p=1 and D=3,p=3,we precisely recover the results of parallel plates and three-dimensional box in the literature.And explicit expressions of the Casimir free energy in both low temperature (small separations and high temperature (large separations regimes are given,through which we find that after the regularization of both parts,with the side length going to infinity the force always tends to zero for different boundary conditions.Our study may be helpful in providing a comprehensive and complete understanding of this old problem.
Weak localization as a definitive test of diffusive models in the Casimir effect
Allocca, Andrew; Wilson, Justin; Galitski, Victor
2015-03-01
Results from many measurements of the Casimir effect suggest that the metallic plates in these experiments should be modeled with the plasma model of free electrons as opposed to the naive diffusive Drude model, while other experiments seem to indicate the exact opposite, with results more in line with a diffusive model. We study the Casimir effect at low temperatures between a thick disordered plate and purely two-dimensional disordered system where the Drude conductivity decreases logarithmically at low temperatures due to weak localization. This effect can be tuned with either temperature or applied magnetic field leading to a measurable change in the Casimir force. On the other hand, a ballistic model cannot experience such an effect and is only weakly dependent on temperature and magnetic field. As a result, we propose that an experiment would unambiguously differentiate between diffusive and ballistic models by measuring the effect at low temperatures with an applied magnetic field. Additionally, we calculate the impact that fluctuations in the disorder distribution have on the Casimir effect. Assuming the validity of a diffusive model, we find that the Drude model is a good approximation of a more exact treatment of disorder. This work was supported by the DOE-BES (Grant No. DESC0001911) (A.A. and V.G.), the JQI-PFC (J.W.), and the Simons Foundation.
Finite temperature Casimir effect for graphene
Fialkovsky, Ignat V; Vassilevich, Dmitri V
2011-01-01
We adopt the Dirac model for quasiparticles in graphene and calculate the finite temperature Casimir interaction between a suspended graphene layer and a parallel conducting surface. We find that at high temperature the Casimir interaction in such system is just one half of that for two ideal conductors separated by the same distance. In this limit single graphene layer behaves exactly as a Drude metal. In particular, the contribution of the TE mode is suppressed, while one of the TM mode saturates the ideal metal value. Behaviour of the Casimir interaction for intermediate temperatures and separations accessible for an experiment is studied in some detail. We also find an interesting interplay between two fundamental constants of graphene physics: the fine structure constant and the Fermi velocity.
Dynamical Casimir effect and quantum cosmology
International Nuclear Information System (INIS)
We apply the background field method and the effective action formalism to describe the four-dimensional dynamical Casimir effect. Our picture corresponds to the consideration of quantum cosmology for an expanding FRW universe (the boundary conditions act as a moving mirror) filled by a quantum massless GUT which is conformally invariant. We consider cases in which the static Casimir energy is attractive and repulsive. Inserting the simplest possible inertial term, we find, in the adiabatic (and semiclassical) approximation, the dynamical evolution of the scale factor and the dynamical Casimir stress analytically and numerically [for SU(2) super Yang-Mills theory]. Alternative kinetic energy terms are explored in the Appendix. (c) 2000 The American Physical Society
Bubble-wall Casimir interaction in fermionic environments
Flachi, Antonino
2015-01-01
We consider the Casimir interaction, mediated by massless fermions, between a spherical defect and a flat potential barrier, assuming hard (bag-type) boundary conditions at both the barrier and the surface of the sphere. The computation of the quantum interaction energy is carried out using the multiple scattering approach, adapted here to the setup in question. We find an exact integral formula for the energy, from which we extract both the large and short distance asymptotic behaviour. At large distance the fermionic contribution is found to scale as $L^{-3}$, in contrast to that of electromagnetic vacuum fluctuations that, assuming perfectly conducting boundaries, scales as $L^{-4}$. At short distance, we compute the leading and sub-leading contribution to the vacuum energy. The leading one coincides with what it is expected from the proximity force approximation, while the sub-leading term gives, contrary to the electromagnetic case, a positive correction to the proximity force result.
Obol, Mahmut
2013-01-01
Ferrites are distinct material for electromagnetic applications due to its unique spin precession. In this paper, Casimir pressure effect by deploying magnetically tunable surface plasmon quanta in stratified structure of using ferrite and metal wires is presented. Previously, oscillating surface plasmon quanta were successfully included to modify first reflection and first transmission characteristics. The oscillating surface plasmon quanta in the modified reflection in such a system, not only does resolve in a typical matter in metamaterial, but also provide new applications such as creating Casimir pressure effects through the metamaterial composite shown in this paper. The Casimir pressure flips from attractive state to repulsive state is referred to actual cause mechanism of radiation from surface plasmon quanta. Both Casimir force analysis and the measured data of radiations indicate us the system develops quantized states by electric flux induced by ferromagnetic resonance, so we also carried quantum a...
Casimir-Polder effect with thermally excited surfaces
Laliotis, A.; Ducloy, M.
2015-05-01
We take a closer look at the fundamental Casimir-Polder (CP) interaction between quantum particles and dispersive dielectric surfaces with surface polariton or plasmon resonances. Linear response theory shows that in the near-field, van der Waals regime the free-energy shift of a particle contains a thermal component that depends exclusively on the excitation of the evanescent surface polariton (plasmon or phonon) modes. Our work makes evident the link between particle surface interaction and near-field thermal emission and demonstrates how this can be used to engineer Casimir-Polder forces. We also examine how the exotic effects of surface waves are washed out as the distance from the surface increases. In the case of molecules or excited-state atoms, far-field approximations result in a classical dipole-dipole interaction which depends on the surface reflectivity and the mean number of photons at the frequency of the atomic or molecular transition. Finally we present numerical results for the CP interaction between Cs atoms and various dielectric surfaces with a single polariton resonance and discuss the implications of temperature and retardation effects for specific spectroscopic experiments.
Casimir-Polder effect with thermally excited surfaces
Laliotis, A
2015-01-01
We take a closer look at the fundamental Casimir-Polder interaction between quantum particles and dispersive dielectric surfaces with surface polariton or plasmon resonances. Linear response theory shows that in the near field, van der Waals, regime the free energy shift of a particle contains a thermal component that depends exclusively on the population/excitation of the evanescent surface polariton/plasmon modes. Our work makes evident the link between particle surface interaction and near field thermal emission and demonstrates how this can be used to engineer Casimir-Polder forces. We also examine how the exotic effects of surface waves are washed out as the distance from the surface increases. In the case of molecules or excited state atoms, far field approximations result in a classical dipole-dipole interaction which depends on the surface reflectivity and the mean number of photons at the frequency of the atomic/molecular transition. Finally we present numerical results for the CP interaction between...
Brane Localization and Stabilization via the Casimir Effect
Jacobs, David M; Tolley, Andrew J
2012-01-01
Extra-dimensional scenarios have become widespread among particle and gravitational theories of physics to address several outstanding problems, including the dark energy or weak hierarchy problems. In general, the topology and geometry of the full spacetime manifold will be non-trivial, even if our ordinary dimensions have the topology of their covering space. Most compact manifolds are inhomogeneous, even if they admit a homogeneous geometry, and it will be physically relevant where in the extra-dimensions one is located. In this letter, we explore the use of the Casimir effect in a braneworld scenario as a dynamical mechanism to determine and stabilize the location of a single brane. This is possible because the zero point energy in bulk quantum fields that satisfy particular brane boundary conditions depends on the brane location. Thus, there is a position-dependent force on the brane. Here we consider the 2-dimensional horn as a toy model of the extra dimensions and calculate the Casimir energy for a bul...
International Nuclear Information System (INIS)
We present supplementary information on the recent indirect measurement of the Casimir pressure between two parallel plates using a micromachined oscillator. The equivalent pressure between the plates is obtained by means of the proximity force approximation after measuring the force gradient between a gold coated sphere and a gold coated plate. The data are compared with a new theoretical approach to the thermal Casimir force based on the use of the Lifshitz formula, combined with a generalized plasma-like dielectric permittivity that takes into account interband transitions of core electrons. The theoretical Casimir pressures calculated using the new approach are compared with those computed in the framework of the previously used impedance approach and also with the Drude model approach. The latter is shown to be excluded by the data at a 99.9% confidence level within the wide separation range from 210 to 620 nm. The level of agreement between the data and theoretical approaches based on the generalized plasma model, or the Leontovich surface impedance, is used to set stronger constraints on the Yukawa forces predicted from the exchange of light elementary particles and/or extra-dimensional physics. The resulting constraints are the strongest in the interaction region from 20 to 86 nm with a largest improvement by a factor of 4.4 at 26 nm. (orig.)
International Nuclear Information System (INIS)
We report stronger constraints on the parameters of Yukawa-type corrections to Newtonian gravity from measurements of the lateral Casimir force between sinusoidally corrugated surfaces of a sphere and a plate. In the interaction range from 1.6 to 14 nm the strengthening of previously known high confidence constraints up to a factor of 2.4x107 is achieved using these measurements. It is shown that the replacement of a plane plate with a corrugated one in the measurements of the normal Casimir force by means of an atomic force microscope would result in the strengthening of respective high confidence constraints on the Yukawa-type interaction by a factor of 1.1x1012. The use of a corrugated plate instead of a plane plate in the experiment by means of a micromachined oscillator also leads to strengthening of the obtained constraints. We further obtain constraints on the parameters of Yukawa-type interaction from the data of experiments measuring the gradient of the Casimir pressure between two parallel plates and the gradient of the Casimir-Polder force between an atom and a plate. The obtained results are compared with the previously known constraints. The possibilities of how to further strengthen the constraints on non-Newtonian gravity are discussed.
Thermal Casimir-Polder shifts in Rydberg atoms near metallic surfaces
Crosse, J. A.; Ellingsen, Simen Å.; Clements, Kate; Buhmann, Stefan Y.; Scheel, Stefan
2010-01-01
The Casimir-Polder (CP) potential and transition rates of a Rydberg atom above a plane metal surface at finite temperature are discussed. As an example, the CP potential and transition rates of a rubidium atom above a copper surface at room temperature is computed. Close to the surface we show that the quadrupole correction to the force is significant and increases with increasing principal quantum number n. For both the CP potential and decay rates one finds that the dominant contribution co...
Casimir stress on lossy magnetodielectric spheres
Raabe, C; Welsch, D G; Raabe, Christian; Knoell, Ludwig; Welsch, Dirk-Gunnar
2003-01-01
An expression for the Casimir stress on arbitrary dispersive and lossy linear magnetodielectric matter at finite temperature, including left-handed material, is derived and applied to spherical systems. To cast the relevant part of the scattering Green tensor for a general magnetodielectric sphere in a convenient form, classical Mie scattering is reformulated.
Borjan, Z.
2016-09-01
We consider critical Casimir force in the Ising strips with boundary conditions defined by standard normal and ordinary surface universality classes containing also the internal grain boundary. Using exact variational approach of Mikheev and Fisher we have elaborated on behaviors of Casimir amplitudes Δ++(g) , ΔOO(g) and Δ+O(g) , corresponding to normal-normal, ordinary-ordinary and mixed normal-ordinary boundary conditions, respectively, with g as a strength of the grain boundary. Closed analytic results describe Casimir amplitudes Δ++(g) and ΔOO(g) as continuous functions of the grain boundary's strength g, changing the character of the Casimir force from repulsive to attractive and vice versa for certain domains of g. Present results reveal a new type of symmetry between Casimir amplitudes Δ++(g) and ΔOO(g) . Unexpectedly simple constant result for the Casimir amplitude Δ+O(g) = π/12 we have comprehensively interpreted in terms of equilibrium states of the present Ising strip as a complex interacting system comprising two sub-systems. Short-distance expansions of energy density profiles in the vicinity of the grain boundary reveal new distant-wall correction amplitudes that we examined in detail. Analogy of present considerations with earlier more usual short-distance expansions near one of the (N), (O) and (SB) boundaries, as well as close to surfaces with variable boundary conditions refers to the set of scaling dimensions appearing in the present calculations but also to the discovery of the de Gennes-Fisher distant wall correction amplitudes.
Nonlinear actuation dynamics of driven Casimir oscillators with rough surfaces
Broer, Wijnand; Svetovoy, Vitaly B; Knoester, Jasper; Palasantzas, George
2015-01-01
At separations below 100 nm, Casimir-Lifshitz forces strongly influence the actuation dynamics of micro-electromechanical systems (MEMS) in dry vacuum conditions. For a micron size plate oscillating near a surface, which mimics a frequently used setup in experiments with MEMS, we show that the roughness of the surfaces significantly influences the qualitative dynamics of the oscillator. Via a combination of analytical and numerical methods, it is shown that surface roughness leads to a clear increase of initial conditions associated with chaotic motion, that eventually lead to stiction between the surfaces. Since stiction leads to malfunction of MEMS oscillators, our results are of central interest for the design of microdevices. Moreover, they are of significance for fundamentally motivated experiments performed with MEMS.
The Casimir effect in light-front quantization
Hiller, J R
2014-01-01
We show that the standard result for the Casimir force between conducting plates at rest in an inertial frame can be computed in light-front quantization. This is not the same as light-front analyses where the plates are at "rest" in an infinite momentum frame. In that case, Lenz and Steinbacher have shown that the result does not agree with the standard result for plates at rest. The two important ingredients in the present analysis are a careful treatment of the boundary conditions, inspired by the work of Almeida et al. on oblique light-front coordinates, and computation of the ordinary energy density, rather than the light-front energy density.
Nonlinear Actuation Dynamics of Driven Casimir Oscillators with Rough Surfaces
Broer, Wijnand; Waalkens, Holger; Svetovoy, Vitaly B.; Knoester, Jasper; Palasantzas, George
2015-11-01
At separations below 100 nm, Casimir-Lifshitz forces strongly influence the actuation dynamics of microelectromechanical systems (MEMS) in dry vacuum conditions. For a micron-size plate oscillating near a surface, which mimics a frequently used setup in experiments with MEMS, we show that the roughness of the surfaces significantly influences the qualitative dynamics of the oscillator. Via a combination of analytical and numerical methods, it is shown that surface roughness leads to a clear increase of initial conditions associated with chaotic motion, that eventually lead to stiction between the surfaces. Since stiction leads to a malfunction of MEMS oscillators, our results are of central interest for the design of microdevices. Moreover, stiction is of significance for fundamentally motivated experiments performed with MEMS.
Why are Casimir energy differences so often finite?
Visser, Matt
2016-01-01
One of the very first applications of the quantum field theoretic vacuum state was in the development of the notion of Casimir energy. Now field theoretic Casimir energies, considered individually, are always infinite. But differences in Casimir energies are quite often finite --- a fortunate circumstance which luckily made some of the early calculations, (for instance, for parallel plates and hollow spheres), tolerably tractable. We shall explore the extent to which this observation can be systematised. For instance: What are necessary and sufficient conditions for Casimir energy differences to be finite? When the Casimir energy differences are not finite, can anything useful be said? We shall see that it is the difference in the first few Seeley-DeWitt coefficients that is central to answering these questions. In particular, for any collection of conductors (perfect or imperfect) and/or dielectrics, as long as one merely moves them around without changing shape or volume, then the Casimir energy difference ...
Electrodynamic Casimir Effect in a Medium-Filled Wedge II
Ellingsen, Simen Adnoy; Brevik, Iver; Milton, Kimball A.
2009-01-01
We consider the Casimir energy in a geometry of an infinite magnetodielectric wedge closed by a circularly cylindrical, perfectly conducting arc embedded in another magnetodielectric medium, under the condition that the speed of light be the same in both media. An expression for the Casimir energy corresponding to the arc is obtained and it is found that in the limit where the reflectivity of the wedge boundaries tends to unity the finite part of the Casimir energy of a perfectly conducting w...
Experiments on Sphere Cylinder Geometry Dependence in the Electromagnetic Casimir Effect
Mukhopadhyay, Shomeek; Noruzifar, Ehsan; Wagner, Jeffrey; Zandi, Roya; Mohideen, Umar
2013-03-01
We report on ongoing experimental investigations on the geometry dependence of the electromagnetic Casimir force in the sphere-cylinder configuration. A gold coated hollow glass sphere which forms one surface is attached to a Silicon AFM cantilever. The cylinder, which is constructed from tapered optical fiber is also gold coated. The resonance frequency shift of the cantilever is measured as a function of the sphere-cylinder surface separation. The sphere-cylinder electrostatic force is used for alignment of the sphere and the cylinder and also for calibrating the system. The results are compared to numerical simulations in the framework of the Proximity Force Approximation (PFA).
Fermionic Casimir interaction in cylinder-plate and cylinder-cylinder geometries
Teo, L P
2015-01-01
In this work, we consider the Casimir effect due to massless fermionic fields in the presence of long cylinders. More precisely, we consider the interaction between a cylinder parallel to a plate, between two parallel cylinders outside each other, and between a cylinder lying parallelly inside another cylinder. We derive the explicit formulas for the Casimir interaction energies and compute the leading and the next-to-leading order terms of the small separation asymptotic expansions. As expected, the leading order terms coincide with the proximity force approximations. We compare the results of the next-to-leading order terms of different quantum fields, and show that our results support the ansatz of derivative expansions.
Thermal diffractive corrections to Casimir energies
Kabat, Daniel
2011-01-01
We study the interplay of thermal and diffractive effects in Casimir energies. We consider plates with edges, oriented either parallel or perpendicular to each other, as well as a single plate with a slit. We compute the Casimir energy at finite temperature using a formalism in which the diffractive effects are encoded in a lower dimensional non-local field theory that lives in the gap between the plates. The formalism allows for a clean separation between direct or geometric effects and diffractive effects, and makes an analytic derivation of the temperature dependence of the free energy possible. At low temperatures, with Dirichlet boundary conditions on the plates, we find that diffractive effects make a correction to the free energy which scales as T^6 for perpendicular plates, as T^4 for slits, and as T^4 log T for parallel plates.
Casimir apparatuses in a weak gravitational field
DEFF Research Database (Denmark)
Bimonte, Giuseppe; Calloni, Enrico; Esposito, Giampiero;
2009-01-01
We review and assess a part of the recent work on Casimir apparatuses in the weak gravitational field of the Earth. For a free, real massless scalar field subject to Dirichlet or Neumann boundary conditions on the parallel plates, the resulting regularized and renormalized energy-momentum tensor...... is covariantly conserved, while the trace anomaly vanishes if the massless field is conformally coupled to gravity. Conformal coupling also ensures a finite Casimir energy and finite values of the pressure upon parallel plates. These results have been extended to an electromagnetic field subject to perfect...... conductor (hence idealized) boundary conditions on parallel plates, by various authors. The regularized and renormalized energy-momentum tensor has beene valuated up to second order in the gravity acceleration. In both the scalar and the electromagnetic case, studied to first order in the gravity...
The character of the supersymmetric Casimir energy
Martelli, Dario
2015-01-01
We study the supersymmetric Casimir energy $E_\\mathrm{susy}$ of $\\mathcal{N}=1$ field theories with an R-symmetry, defined on rigid supersymmetric backgrounds $S^1\\times M_3$, using a Hamiltonian formalism. These backgrounds admit an ambi-Hermitian geometry, and we show that the net contributions to $E_\\mathrm{susy}$ arise from certain twisted holomorphic modes on $\\mathbb{R}\\times M_3$, with respect to both complex structures. The supersymmetric Casimir energy may then be identified as a limit of an index-character that counts these modes. In particular this explains a recent observation relating $E_\\mathrm{susy}$ on $S^1\\times S^3$ to the anomaly polynomial. As further applications we compute $E_\\mathrm{susy}$ for certain secondary Hopf surfaces, and discuss how the index-character may also be used to compute generalized supersymmetric indices.
Curved Casimir Operators and the BGG Machinery
Directory of Open Access Journals (Sweden)
Andreas Cap
2007-11-01
Full Text Available We prove that the Casimir operator acting on sections of a homogeneous vector bundle over a generalized flag manifold naturally extends to an invariant differential operator on arbitrary parabolic geometries. We study some properties of the resulting invariant operators and compute their action on various special types of natural bundles. As a first application, we give a very general construction of splitting operators for parabolic geometries. Then we discuss the curved Casimir operators on differential forms with values in a tractor bundle, which nicely relates to the machinery of BGG sequences. This also gives a nice interpretation of the resolution of a finite dimensional representation by (spaces of smooth vectors in principal series representations provided by a BGG sequence.
Curved Casimir Operators and the BGG Machinery
Cap, Andreas; Soucek, Vladimír
2007-11-01
We prove that the Casimir operator acting on sections of a homogeneous vector bundle over a generalized flag manifold naturally extends to an invariant differential operator on arbitrary parabolic geometries. We study some properties of the resulting invariant operators and compute their action on various special types of natural bundles. As a first application, we give a very general construction of splitting operators for parabolic geometries. Then we discuss the curved Casimir operators on differential forms with values in a tractor bundle, which nicely relates to the machinery of BGG sequences. This also gives a nice interpretation of the resolution of a finite dimensional representation by (spaces of smooth vectors in) principal series representations provided by a BGG sequence.
The Casimir effect in minimal length theories
Energy Technology Data Exchange (ETDEWEB)
Frassino, Antonia Micol [Frankfurt Institute for Advanced Studies (Germany); Panella, Orlando [INFN, Perugia (Italy); Universita di Perugia (Italy)
2012-07-01
We start by a brief review of the Casimir effect. Then we study how this effect is sensible to the smaller structure of spacetime. To achieve this, we model spacetime granularity by the presence of a minimal length implemented through a generalized uncertainty principle. We find that the quantization of the electromagnetic field is affected by the minimal length: specifically, fields can be only expanded on a set of maximally localized states that regularize the UV region of the theory. In this context we compute the lowest order correction in the minimal length parameter to the Casimir energy. We find that the correction is still attractive and scales with the fifth power of the distance between the plates. We make some considerations about the possibility of observing this effect. Future developments are suggested.
Maxwell-Chern-Simons Casimir Effect
Milton, K A
1992-01-01
In odd-dimensional spaces, gauge invariance permits a Chern-Simons mass term for the gauge fields in addition to the usual Maxwell-Yang-Mills kinetic energy term. We study the Casimir effect in such a (2+1)-dimensional Abelian theory. For the case of parallel conducting lines the result is the same as for a scalar field. For the case of circular boundary conditions the results are completely different, with even the sign of the effect being opposite for Maxwell-Chern-Simons fields and scalar fields. We further examine the effect of finite temperature. The Casimir stress is found to be attractive at both low and high temperature. Possibilities of observing this effect in the laboratory are discussed.
Casimir effect in dielectrics Surface area contribution
Molina-Paris, C; Molina-Paris, Carmen; Visser, Matt
1997-01-01
In this paper we take a deeper look at the technically elementary but physically robust viewpoint in which the Casimir energy in dielectric media is interpreted as the change in the total zero point energy of the electromagnetic vacuum summed over all states. Extending results presented in previous papers [hep-th/9609195; hep-th/9702007] we approximate the sum over states by an integral over the density of states including finite volume corrections. For an arbitrarily-shaped finite dielectric, the first finite-volume correction to the density of states is shown to be proportional to the surface area of the dielectric interface and is explicitly evaluated as a function of the permeability and permitivity. Since these calculations are founded in an elementary and straightforward way on the underlying physics of the Casimir effect they serve as an important consistency check on field-theoretic calculations. As a concrete example we discuss Schwinger's suggestion that the Casimir effect might be the underlying ph...
Casimir effect in dielectrics: Bulk energy contribution
International Nuclear Information System (INIS)
In a recent series of papers, Schwinger discussed a process that he called the dynamical Casimir effect. The key essence of this effect is the change in zero-point energy associated with any change in a dielectric medium. (In particular, if the change in the dielectric medium is taken to be the growth or collapse of a bubble, this effect may have relevance to sonoluminescence.) The kernel of Schwinger close-quote s result is that the change in Casimir energy is proportional to the change in the volume of the dielectric, plus finite-volume corrections. Other papers have called into question this result, claiming that the volume term should actually be discarded, and that the dominant term remaining is proportional to the surface area of the dielectric. In this paper, which is an expansion of an earlier Letter on the same topic, we present a careful and critical review of the relevant analyses. We find that the Casimir energy, defined as the change in zero-point energy due to a change in the medium, has at leading order a bulk volume dependence. This is in full agreement with Schwinger close-quote s result, once the correct physical question is asked. We have nothing new to say about sonoluminescence itself. copyright 1997 The American Physical Society
Casimir-Polder interaction in second quantization
Energy Technology Data Exchange (ETDEWEB)
Schiefele, Juergen
2011-03-21
The Casimir-Polder interaction between a single neutral atom and a nearby surface, arising from the (quantum and thermal) fluctuations of the electromagnetic field, is a cornerstone of cavity quantum electrodynamics (cQED), and theoretically well established. Recently, Bose-Einstein condensates (BECs) of ultracold atoms have been used to test the predictions of cQED. The purpose of the present thesis is to upgrade single-atom cQED with the many-body theory needed to describe trapped atomic BECs. Tools and methods are developed in a second-quantized picture that treats atom and photon fields on the same footing. We formulate a diagrammatic expansion using correlation functions for both the electromagnetic field and the atomic system. The formalism is applied to investigate, for BECs trapped near surfaces, dispersion interactions of the van der Waals-Casimir-Polder type, and the Bosonic stimulation in spontaneous decay of excited atomic states. We also discuss a phononic Casimir effect, which arises from the quantum fluctuations in an interacting BEC. (orig.)
Scalar cylinder-plate and cylinder-cylinder Casimir interaction in higher dimensional spacetime
Teo, L P
2015-01-01
We study the cylinder-plate and the cylinder-cylinder Casimir interaction in the $(D+1)$-dimensional Minkowski spacetime due to the vacuum fluctuations of massless scalar fields. Different combinations of Dirichlet (D) and Neumann (N) boundary conditions are imposed on the two interacting objects. For the cylinder-cylinder interaction, we consider the case where one cylinder is inside the other, and the case where the two cylinders are outside each other. By computing the transition matrices of the objects and the translation matrices that relate different coordinate systems, the explicit formulas for the Casimir interaction energies are derived. Using perturbation technique, we compute the small separation asymptotic expansions of the Casimir interaction energies up to the next-to-leading order terms. The leading terms coincide with the respective results obtained using proximity force approximation, which is of order $d^{-D+1/2}$, where $d$ is the distance between the two objects. The results on the next-to...
Scalar cylinder-plate and cylinder-cylinder Casimir interaction in higher dimensional spacetime
Teo, Lee-Peng
2015-07-01
We study the cylinder-plate and the cylinder-cylinder Casimir interaction in the (D +1 )-dimensional Minkowski spacetime due to the vacuum fluctuations of massless scalar fields. Different combinations of Dirichlet (D) and Neumann (N) boundary conditions are imposed on the two interacting objects. For the cylinder-cylinder interaction, we consider the case where one cylinder is inside the other and the case where the two cylinders are outside each other. By computing the transition matrices of the objects and the translation matrices that relate different coordinate systems, the explicit formulas for the Casimir interaction energies are derived. From these formulas, we compute the large separation and small separation asymptotic behaviors of the Casimir interaction. For the cylinder-plate interaction with R ≪L , where R is the radius of the cylinder and L is the distance from the center of the cylinder to the plate, the order of decay of the Casimir interaction only depends on the boundary conditions imposed on the cylinder. The orders are L-D +1/ln (L ) and L-D -1/ln L , respectively, for the Dirichlet and Neumann boundary conditions on the cylinder. For two cylinders with radii R1 and R2 lying parallelly outside each other, the orders of decay of the Casimir interaction energies when R1+R2≪L are L-D +1/(ln L )2, L-D -1/ln L , and L-D -3, respectively, for DD, DN/ND, and NN boundary conditions, where L is the distance between the centers of the cylinders. The more interesting and important characteristic of Casimir interaction appears at small separation. Using the perturbation technique, we compute the small separation asymptotic expansions of the Casimir interaction energies up to the next-to-leading-order terms. The leading terms coincide with the respective results obtained using the proximity force approximation, which is of order d-D +1 /2 , where d is the distance between the two objects. The results on the next-to-leading-order terms are more
Casimir energies of self-similar plate configurations
Shajesh, K. V.; Brevik, Iver; Cavero-Peláez, Inés; Parashar, Prachi
2016-09-01
We construct various self-similar configurations using parallel δ -function plates and show that it is possible to evaluate the Casimir interaction energy of these configurations using the idea of self-similarity alone. We restrict our analysis to interactions mediated by a scalar field, but the extension to the electromagnetic field is immediate. Our work unveils an easy and powerful method that can be easily employed to calculate the Casimir energies of a class of self-similar configurations. As a highlight, in an example, we determine the Casimir interaction energy of a stack of parallel plates constructed by positioning δ -function plates at the points constituting the Cantor set, a prototype of a fractal. This, to our knowledge, is the first time that the Casimir energy of a fractal configuration has been reported. Remarkably, the Casimir energy of some of the configurations we consider turn out to be positive, and a few even have zero Casimir energy. For the case of positive Casimir energy that is monotonically decreasing as the stacking parameter increases, the interpretation is that the pressure of vacuum tends to inflate the infinite stack of plates. We further support our results, derived using the idea of self-similarity alone, by rederiving them using the Green's function formalism. These expositions gives us insight into the connections between the regularization methods used in quantum field theories and regularized sums of divergent series in number theory.
Electromagnetic Casimir effect for conducting plates in de Sitter spacetime
Kotanjyan, A S; Nersisyan, H A
2015-01-01
Two-point functions, the mean field squared and the vacuum expectation value (VEV) of the energy-momentum tensor are investigated for the electromagnetic field in the geometry of parallel plates on background of $(D+1)$% -dimensional dS spacetime. We assume that the field is prepared in the Bunch-Davies vacuum state and on the plates a boundary condition is imposed that is a generalization of the perfectly conducting boundary condition for an arbitrary number of spatial dimensions. It is shown that for $D\\geq 4$ the background gravitational field essentially changes the behavior of the VEVs at separations between the plates larger than the curvature radius of dS spacetime. At large separations, the Casimir forces are proportional to the inverse fourth power of the distance for all values of spatial dimension $D\\geq 3$. For $D\\geq 4$ this behavior is in sharp contrast with the case of plates in Minkowski bulk where the force decays as the inverse $(D+1)$th power of the distance.
Farrokhabadi, Amin; Mohebshahedin, Abed; Rach, Randolph; Duan, Jun-Sheng
2016-01-01
The influence of the surface energy on the instability of nano-structures under the electrostatic force has been investigated in recent years by different researchers. It appears that in all prior research, the response of all structures becomes softer due to the surface effects. In the present study, the pull-in instability of a NEMS device incorporating the electrostatic force and Casimir intermolecular attraction for different values of the surface parameter is investigated by the Duan-Rach method of determined coefficients (MDC) in order to identify the remarkable effect of the surface energy. Although the obtained results verify the behavior of such structures in presence of the fringing field and the Casimir attraction same as the previous investigations, however the incremental effects of the surface energy cause the aforementioned structures to behave more stiffly in contrast.
Casimir energy for spherical shell in Schwarzchild black hole background
Setare, M R
2004-01-01
In this paper, we consider the Casimir energy of massless scalar field which satisfy Dirichlet boundary condition on a spherical shell. Outside the shell, the spacetime is assumed to be described by the Schwarzschild metric, while inside the shell it is taken to be the flat Minkowski space. Using zeta function regularization and heat kernel coefficients we isolate the divergent contributions of the Casimir energy inside and outside the shell, then using the renormalization procedure of the bag model the divergent parts are cancelled, finally obtaining a renormalized expression for the total Casimir energy.
Casimir operators of groups of motion of constant curvature spaces
International Nuclear Information System (INIS)
Limit transitions between generating operators (Casimir operators) of the centre of universal enveloping algebra are constructed for Lie algebras of groups of motion of n-dimensional constant curvature spaces (CCS). A method for constructing Casimir operators of the group of motion of an arbitrary n-dimensional CCS from Casimir operators of the group SO(n+1) is formulated. The method is illustrated by the examples of groups of motion of 4-dimensional CCS: Galilei, Poincare, Lobachevsky, De Sitter, Carroll and other spaces
Boström, Mathias; Sernelius, Bo; Baldissera, Gustavo; Persson, Clas; Ninham, Barry W.
2012-01-01
We consider the interaction between a ZnO nanorod and a SiO2 nanorod in bromobenzene. Using optical data for the interacting objects and ambient we calculate the force (from short-range attractive van der Waals force to intermediate-range repulsive Casimir-Lifshitz force to long-range entropically driven attraction). The nonretarded van der Waals interaction is attractive at all separations. We demonstrate a retardation-driven repulsion at intermediate separations. At short separations (in th...
Off-critical Casimir effect in Ising slabs with antisymmetric boundary conditions in d=3
Upton, P.J.; Borjan, Z.
2013-01-01
The universal scaling function W+−(y) of the Casimir force (y is a temperature-dependent variable) away from the critical point for thermodynamic systems in the Ising universality class confined between two parallel plates with antisymmetric boundary conditions [denoted (ab)=(+−)] has been analyzed using the extended de Gennes–Fisher local-functional method. Results on the universal function W+−(y) are presented in spatial dimension d=3 applying the extended sine parametric model for temperat...
Dynamical Casimir effect for surface plasmon polaritons
Energy Technology Data Exchange (ETDEWEB)
Hizhnyakov, V.; Loot, A., E-mail: ardi.loot@ut.ee; Azizabadi, S.Ch.
2015-02-20
The emission of photon pairs by a metal–dielectric interface placed between the mirrors of the resonator and excited by a plane wave is considered. The excitation causes oscillations in time of the optical length of surface plasmon polaritons in the interface. This leads to the dynamical Casimir effect – the generation of pairs of surface plasmon polariton quanta, which transfer to photons outside the interface. In the case of a properly chosen interface, the yield of two-photon emission may exceed that of the usual spontaneous parametric down-conversion. - Highlights: • The theory of dynamical Casimir effect (DCE) in the metal–dielectric interface excited by a monochromatic wave is proposed. • It is shown that the field enhancement associated with surface plasmon polaritons strongly enhances the yield of the DCE. • The numerical calculations of the enhancement factor are made. • The scheme of experimental setup to observe the DCE in the metal–dielectric interface is proposed. • Additional methods to enhance the DCE in the metal–dielectric interface are discussed.
Edges and Diffractive Effects in Casimir Energies
Kabat, Daniel; Nair, V P
2010-01-01
The prototypical Casimir effect arises when a scalar field is confined between parallel Dirichlet boundaries. We study corrections to this when the boundaries themselves have apertures and edges. We consider several geometries: a single plate with a slit in it, perpendicular plates separated by a gap, and two parallel plates, one of which has a long slit of large width, related to the case of one plate being semi-infinite. We develop a general formalism for studying such problems, based on the wavefunctional for the field in the gap between the plates. This formalism leads to a lower dimensional theory defined on the open regions of the plates or boundaries. The Casimir energy is then given in terms of the determinant of the nonlocal differential operator which defines the lower dimensional theory. We develop perturbative methods for computing these determinants. Our results are in good agreement with known results based on Monte Carlo simulations. The method is well suited to isolating the diffractive contri...
Macroscopic QED in linearly responding media and a Lorentz-Force approach to dispersion forces
Energy Technology Data Exchange (ETDEWEB)
Raabe, Christian
2008-07-08
In this thesis, a very general quantization scheme for the macroscopic electromagnetic field in arbitrary linearly responding media is presented. It offers a unified approach to QED in such media. Applying the quantization scheme, a theory of the dispersion forces on the basis of the Lorentz force is developed. By regarding the dispersion force as the (ground-state or thermal-state) expectation value of the Lorentz force that acts on appropriately defined charge and current densities, Casimir, Casimir-Polder, and van der Waals forces are united in a very natural way that makes transparent their common physical basis. Application of the theory to planar structures yields generalizations of well-known Lifschitz and Casimir-type formulas. (orig.)
On the Casimir effect in the microelectromechanical systems MEMS
Marciak-Kozlowska, Janina; Kozlowski, Miroslaw
2005-01-01
In this paper the thermal transport phenomena in MEMS are investigated. The thermal Klein-Gordon transport equation for nanoscale structures is formulated and solved. Key words: MEMS, Klein-Gordon equation, Casimir effect.
Casimir self-energy of a free electron
Rosencwaig, Allan
2006-01-01
We derive the electromagnetic self-energy and the radiative correction to the gyromagnetic ratio of a free electron using a Casimir energy approach. This method provides an attractive and straightforward physical basis for the renormalization process.
The complete set of Casimirs in Hall-MHD
Kawazura, Yohei; Hameiri, Eliezer
2012-03-01
A procedure to determine all Casimir constants of motion in MHDfootnotetextE. Hameiri, Phy. Plasmas, 11, 3423 (2004). is extended to Hall-MHD. We obtain differential equations for the variational derivatives of all Casimirs which must be satisfied for any dynamically accessible motion of Hall-MHD. In an extension of the more commonly considered model, we also include the electron fluid entropy. The most interesting case, usually true for axisymmetric configurations, is when both the electron and ion entropy functions form families of nested toroidal surfaces. The Casimirs are then three functions of each of the entropies, involving fluxes of certain vector fields and the number of particles contained in each torus. If any of the species loses its nested tori, the number of the associated Casimirs is much larger (but physically less relevant).
The complete set of Casimirs in Hall-magnetohydrodynamics
Kawazura, Yohei; Hameiri, Eliezer
2012-08-01
A procedure for determining all the Casimir constants of motion in magnetohydrodynamics (MHD) [E. Hameiri, Phys. Plasmas 11, 3423 (2004)] is extended to Hall-MHD. We obtain and solve differential equations for the variational derivatives of all the Casimirs, which must be satisfied for any dynamically accessible motion in Hall-MHD. In an extension of the more commonly considered Hall-MHD model, we also include the electron fluid entropy. The most interesting case for plasma confinement, which is usually true for axisymmetric configurations but desirable in general, is when both the magnetic field and the ion velocity field form the two separate families of nested toroidal surfaces. The Casimirs are then three functionals for each surface, involving the fluxes of certain vector fields and the number of particles contained in each. We also determine a family of independent Casimirs in a general configuration.
Casimir Energy and Vacua vor Superconducting Ball in Supergravity
Burinskii, A
2002-01-01
Casimir energy for solid conducting ball is considered on the base of some finite models. One model is physical and built of a battery of parallel metallic plates. Two finite models are based on the Higgs model of superconductivity. One of them is supersymmetric and based on the Witten field model for superconducting strings. Treatment shows that contribution of Casimir energy can be very essential for superdence state in the neutron stars and nuclear matter.
The quantum Casimir operators of $\\Uq$ and their eigenvalues
Li, Junbo
2010-01-01
We show that the quantum Casimir operators of the quantum linear group constructed in early work of Bracken, Gould and Zhang together with one extra central element generate the entire center of $\\Uq$. As a by product of the proof, we obtain intriguing new formulae for eigenvalues of these quantum Casimir operators, which are expressed in terms of the characters of a class of finite dimensional irreducible representations of the classical general linear algebra.
Dynamical Casimir effect in Circuit QED for Nonuniform Trajectories
Corona-Ugalde, Paulina; Wilson, C M; Mann, Robert B
2015-01-01
We propose a generalization of the superconducting circuit simulation of the dynamical Casimir effect where we consider relativistically moving boundary conditions following different trajectories. We study the feasibility of the setup used in the past to simulate the dynamical Casimir effect to reproduce richer relativistic trajectories differing from purely sinusoidal ones. We show how different relativistic oscillatory trajectories of the boundaries of the same period and similar shape produce a rather different spectrum of particles characteristic of their respective motions.
How to confirm and exclude different models of material properties in the Casimir effect
International Nuclear Information System (INIS)
We formulate a method allowing us to confirm or exclude the alternative models of material properties at some definite confidence level in experiments on measuring the Casimir force. The method is based on the consideration of differences between the theoretical and mean measured quantities and the confidence intervals for these differences found at sufficiently high or low confidence probabilities. The developed method is applied to the data of four recent experiments on measuring the gradient of the Casimir force by means of a dynamic atomic force microscope. It is shown that in experiments with Au–Au and Ni–Ni test bodies, where the Drude model approach is excluded at a 95% confidence level, the plasma model approach agrees with the data at higher than 90% confidence. In experiments using an Au sphere interacting with either a Ni plate or a graphene-coated substrate, the measurement data agree with the common prediction of the Drude and plasma model approaches and theory using the polarization tensor at 90% and 80% confidence levels, respectively. (paper)
International Nuclear Information System (INIS)
Casimir friction between a polarizable particle and a semi-infinite space is a delicate physical phenomenon, as it concerns the interaction between a microscopic quantum particle and a semi-infinite reservoir. Not unexpectedly, results obtained in the past about the friction force obtained via different routes are sometimes, at least apparently, wildly different from each other. Recently, we considered the Casimir friction force for two dielectric semi-infinite plates moving parallel to each other Høye and Brevik (2014 Eur. Phys. J. D 68 61), and managed to get essential agreement with results obtained by Pendry (1997 J. Phys.: Condens. Matter 9 10301), Volokitin and Persson (2007 Rev. Mod. Phys. 79 1291), and Barton (2011 New J. Phys. 13 043023; 2011 J. Phys.: Condens. Matter 23 335004). Our method was based upon use of the Kubo formalism. In the present paper we focus on the interaction between a polarizable particle and a dielectric half-space again, and calculate the friction force using the same basic method as before. The new ingredient in the present analysis is that we take into account radiative damping, and derive the modifications thereof. Some comparisons are also made with works from others. Essential agreement with the results of Intravaia, Behunin, and Dalvit can also be achieved using the modification of the atomic polarizability by the metallic plate. (paper)
Light-front analysis of the Casimir effect
Chabysheva, Sophia S
2013-01-01
The Casimir force between conducting plates at rest in an inertial frame is usually computed in equal-time quantization, the natural choice for the given boundary conditions. We show that the well-known result obtained in this way can also be obtained in light-front quantization. This differs from a light-front analysis where the plates are at "rest" in an infinite momentum frame, rather than an inertial frame; in that case, as shown by Lenz and Steinbacher, the result does not agree with the standard result. As is usually done, the analysis is simplified by working with a scalar field and periodic boundary conditions, in place of the complexity of quantum electrodynamics. The two key ingredients are a careful implementation of the boundary conditions, following the work of Almeida et al. on oblique light-front coordinates, and computation of the ordinary energy density, rather than the light-front energy density. The analysis demonstrates that the physics of the effect is independent of the coordinate choice...
Casimir-Polder repulsion: Three-body effects
Milton, Kimball A; Parashar, Prachi; Pourtolami, Nima; Brevik, Iver; Ellingsen, Simen A; Buhmann, Stefan Yoshi; Scheel, Stefan
2015-01-01
In this paper we study an archetypical scenario in which repulsive Casimir-Polder forces between an atom or molecule and two macroscopic bodies can be achieved. This is an extension of previous studies of the interaction between a polarizable atom and a wedge, in which repulsion occurs if the atom is sufficiently anisotropic and close enough to the symmetry plane of the wedge. A similar repulsion occurs if such an atom passes a thin cylinder or a wire. An obvious extension is to compute the interaction between such an atom and two facing wedges, which includes as a special case the interaction of an atom with a conducting screen possessing a slit, or between two parallel wires. To this end we further extend the electromagnetic multiple-scattering formalism for three-body interactions. To test this machinery we reinvestigate the interaction of a polarizable atom between two parallel conducting plates. In that case, three-body effects are shown to be small, and are dominated by three- and four-scattering terms....
On the dynamical Casimir effect in 1 + 1 dimensions
International Nuclear Information System (INIS)
Full text follows: Vacuum field fluctuations exert radiation pressure on boundaries placed in empty space. If we take only one boundary at rest in vacuum, the total pressure exerted by the vacuum on the boundary is null. For two boundaries at rest in vacuum there is a net pressure exerted on the boundaries known as the Casimir effect. It has also been recognized that the dynamical counterparts of this static force appear for moving boundaries. In the dynamical case the existence of a net vacuum radiation pressure does not require the presence of two boundaries as in static case. Vacuum pressure already exists for a single boundary moving with a nonuniform acceleration. For that type of motion, the field does not remain in the vacuum state, but the quanta of the field are produced through nonadiabatic processes. In 1982 Ford and Vilenkin developed a perturbation method based on the static solution to calculate in first approximation the vacuum pressure exerted on a non-relativistic moving boundary. Using the method of Ford-Vilenkin we compute in the two dimensional quantum theory of a real massless scalar field the pressure exerted by the vacuum on a perfectly reflecting boundary moving with nonuniform acceleration around the coordinate x = 0 , having another boundary fixed at x = L. This simple model can provide insight into more sophisticated processes, such as photon production by moving mirrors and particle production in cosmological models and exploding black holes. (author)
The Transplanckian Question and the Casimir Effect
Bachmann, S
2005-01-01
It is known that, through inflation, Planck scale phenomena should have left an imprint in the cosmic microwave background. The magnitude of this imprint is expected to be suppressed by a factor $\\sigma^n$ where $\\sigma\\approx 10^{-5}$ is the ratio of the Planck length to the Hubble length during inflation. While there is no consensus about the value of $n$, it is generally thought that $n$ will determine whether the imprint is observable. Here, we suggest that the magnitude of the imprint may not be suppressed by any power of $\\sigma$ and that, instead, $\\sigma$ may merely quantify the amount of fine tuning required to achieve an imprint of order one. To this end, we show that the UV/IR scale separation, $\\sigma$, in the analogous case of the Casimir effect plays exactly this role.
Radiative dark-bright instability and the critical Casimir effect in DQW exciton condensates
Hakioğlu, T.; Özgün, Ege
2011-07-01
It is already well known that radiative interband interaction in the excitonic normal liquid in semiconducting double quantum wells is responsible for a negligible splitting between the energies of the dark and bright excitons enabling us to consider a four fold spin degeneracy. This has also lead many workers to naively consider the same degeneracy in studying the condensate. On the other hand, the non-perturbative aspects of this interaction in the condensed phase, e.g. its consequences on the order parameter and the dark-bright mixture in the ground state have not been explored. In this work, we demonstrate that the ground state concentrations of the dark and the bright exciton condensates are dramatically different beyond a sharp interband coupling threshold where the contribution of the bright component in the ground state vanishes. This shows that the effect of the radiative interband interaction on the condensate is nonperturbative. We also observe in the free energy a discontinuous derivative with respect to the layer separation at the entrance to the condensed phase, indicating a strong critical Casimir force. An estimate of its strength shows that it is measurable. Measuring the Casimir force is challenging, but at the same time it has a conclusive power about the presence of the long sought for condensed phase.
Casimir free energy and pressure for magnetic metal films
Klimchitskaya, G. L.; Mostepanenko, V. M.
2016-07-01
We examine the Casimir free energy and pressure of magnetic metal films, which are free standing in vacuum, sandwiched between two dielectric plates and deposited on either nonmagnetic or magnetic metallic plates. All calculations are performed using both the Drude and plasma model approaches to the Lifshitz theory. According to our results, the Casimir free energies and pressures calculated using both theoretical approaches are significantly different in the magnitude and sign even for thin films of several tens of nanometers thickness. Thus, for the Ni film of 47 nm thickness deposited on a Fe plate the obtained magnitudes of the Casimir free energy differ by the factor of 5866. We show that the Casimir free energy and pressure of a magnetic film calculated using the plasma model approach do not possess the classical limit but exponentially fast drop to zero with increasing film thickness. If the Drude model approach is used, the classical limit is reached for magnetic films of about 150 nm thickness, but the Casimir free energy remains nonzero in the limit of ideal metal, contrary to expectations. For the plasma model approach the Casimir free energy of a film vanishes in this case. Numerical computations are performed for the magnetic films made of Ni, nonmagnetic plates made of Cu and Al, and magnetic plates made of Fe using the tabulated optical data for the complex indexes of refraction of all metals. The obtained results can be used for a discrimination between the plasma and Drude model approaches in the Casimir physics and in the investigation of stability of thin films.
International Nuclear Information System (INIS)
We discuss the constraints on the parameters of a Yukawa interaction obtained from the indirect measurements of the Casimir pressure between parallel plates using the sphere-plate configuration. Recently, it was claimed in the literature that the application of the proximity force approximation (PFA) to the calculation of a Yukawa interaction in the sphere-plate configuration could lead to a large error of order 100% in the constraints obtained. Here we re-calculate the constraints both exactly and using the PFA, and arrive at identical results. We elucidate the reasons why an incorrect conclusion was obtained suggesting that the PFA is inapplicable to calculate the Yukawa force. (orig.)
Test of non-Newtonian gravitational force at micrometer range
Luo, Pengshun; Wang, Jianbo; Guan, Shengguo; Wu, Wenjie; Tian, Zhaoyang; Yang, Shanqing; Shao, Chenggang; Luo, Jun
2016-01-01
We report an experimental test of non-Newtonian gravitational forces at mi- crometer range. To experimentally subtract off the Casimir force and the electrostatic force background, differential force measurements were performed by sensing the lateral force between a gold sphere and a density modulated source mass using a soft cantilever. The current sensitivity is limited by the patch electrostatic force, which is further improved by two dimensional (2D) force mapping. The preliminary result ...
Pressures and Energies in Magnetized Vacuum and in Casimir effect
Rojas, H P
2004-01-01
We study vacuum pressures and energies for electron-positron vacuum zero point energy in a strong magnetic field $B$ and for photon vacuum in Casimir effect, by a common method. Vacuum becomes magnetized, and due to it, the pressure transversal to $B$ is negative, whereas along $B$ an usual positive pressure arises. Similarly, in addition to the usual negative Casimir pressure perpendicular to the plates, the existence of a positive pressure along the plates is predicted. Both vacua bear the property of leading to a negative energy-momentum tensor trace ${\\cal T}_{\\mu}^{\\mu}<0$, which may lead to a repulsive gravity typical of dark energy. By assuming a space distribution of magnetic and/or Casimir domains, cosmological implications are also discussed.
Casimir Effect in the Kerr Spacetime Surrounded by Quintessence
Bezerra, V B; Freitas, L F F; Muniz, C R
2016-01-01
We calculate the Casimir energy of a massless scalar field in a cavity formed by nearby parallel plates orbiting a rotating spherical body surrounded by quintessence, investigating the influence of the gravitational field on that energy, at zero temperature. This influence includes the effects due to the spacetime dragging caused by the source rotation as well as those ones due to the quintessence. We show that the energy depends on all the involved parameters, as source mass, angular momentum and quintessence state parameter, for any radial coordinate and polar angle. We show that at the north pole the Casimir energy is not influenced by the quintessential matter. At the equatorial plane, when the quintessence is canceled, the result obtained in the literature is recovered. Finally, constraints in the quintessence parameters are obtained from the uncertainty in the current measurements of Casimir effect.
Evanescent radiation, quantum mechanics and the Casimir effect
Schatten, Kenneth H.
1989-01-01
An attempt to bridge the gap between classical and quantum mechanics and to explain the Casimir effect is presented. The general nature of chaotic motion is discussed from two points of view: the first uses catastrophe theory and strange attractors to describe the deterministic view of this motion; the underlying framework for chaos in these classical dynamic systems is their extreme sensitivity to initial conditions. The second interpretation refers to randomness associated with probabilistic dynamics, as for Brownian motion. The present approach to understanding evanescent radiation and its relation to the Casimir effect corresponds to the first interpretation, whereas stochastic electrodynamics corresponds to the second viewpoint. The nonlinear behavior of the electromagnetic field is also studied. This well-understood behavior is utilized to examine the motions of two orbiting charges and shows a closeness between the classical behavior and the quantum uncertainty principle. The evanescent radiation is used to help explain the Casimir effect.
Casimir operator dependences of non-perturbative fermionic QCD amplitudes
Fried, H M; Hofmann, R
2015-01-01
In eikonal and quenched approximation, it is argued that the strong coupling fermionic QCD Green's functions and related amplitudes, when based on the newly discovered effective locality property, depart from a sole dependence on the SUc(3) quadratic Casimir operator, evaluated over the fundamental gauge group representation.Though noticed in non-relativistic Quark Models, an additional dependence on the cubic Casimir operator is in contradistinction with perturbation theory, and also with a number of non-perturbative approaches such as the MIT Bag, the Stochastic Vacuum Models and lattice simulations. It accounts for the full algebraic content of the rank-2 Lie algebra of SUc(3). We briefly discuss the orders of magnitude of quadratic and cubic Casimir operator contributions.
Computing the Casimir energy using the point-matching method
Lombardo, F C; Váquez, M; Villar, P I
2009-01-01
We use a point-matching approach to numerically compute the Casimir interaction energy for a two perfect-conductor waveguide of arbitrary section. We present the method and describe the procedure used to obtain the numerical results. At first, our technique is tested for geometries with known solutions, such as concentric and eccentric cylinders. Then, we apply the point-matching technique to compute the Casimir interaction energy for new geometries such as concentric corrugated cylinders and cylinders inside conductors with focal lines.
Casimir Energies on a Twisted Two-Torus
Institute of Scientific and Technical Information of China (English)
程红波; 李新洲
2001-01-01
We consider a twisted massless multiplet on a two-torus, one side with a normal boundary and the other with a twisted boundary. The Casimir energy is calculated and regularized by means of the Epstein-Hurwitz-type zeta-function introduced by Elizalde. The resulting dimensions of spacetime for the twisted case may be integers.The results are compared with those of the untwisted case. Since twisted Casimir energy is lower than untwisted energy, the untwisted case may change into the twisted state in the spacetime.
Casimir invariants and characteristic identities for $gl(\\infty )$
Gould, M D
1997-01-01
A full set of (higher order) Casimir invariants for the Lie algebra $gl(\\infty )$ is constructed and shown to be well defined in the category $O_{FS}$ generated by the highest weight (unitarizable) irreducible representations with only a finite number of non-zero weight components. Moreover the eigenvalues of these Casimir invariants are determined explicitly in terms of the highest weight. Characteristic identities satisfied by certain (infinite) matrices with entries from $gl(\\infty )$ are also determined and generalize those previously obtained for $gl(n)$ by Bracken and Green.$^{1,2}$
The Casimir-Polder interaction an atom with spherical shell
Khusnutdinov, Nail
2014-01-01
The Casimir-Polder and van der Waals interaction energy of an atom with infinitely thin sphere with finite conductivity is investigated in the framework of the hydrodynamic approach. We put the sphere into spherical cavity inside the infinite dielectric media, then calculate the energy of vacuum fluctuations in the context of the zeta-function approach. The energy for a single atom is obtained by rarefying media. The Casimir-Polder expression for an atom and plate is recovered in the limit of...
One-loop radiative corrections to the QED Casimir energy
Energy Technology Data Exchange (ETDEWEB)
Moazzemi, Reza; Mojavezi, Amirhosein [University of Qom, Department of Physics, Qom (Iran, Islamic Republic of)
2016-05-15
In this paper, we investigate one-loop radiative corrections to the Casimir energy in the presence of two perfectly conducting parallel plates for QED theory within the renormalized perturbation theory. In fact, there are three contributions for radiative corrections to the Casimir energy, up to order α, has been computed by Bordag et. al (Ann. Phys. 165:192, 1985), approximately. Here, up to this order, we consider corrections due to two one-loop terms, i.e., photonic and fermionic loop corrections resulting from renormalized QED Lagrangian, more precisely. Our results show that only the fermionic loop has a very minor correction and the correction of photonic loop vanishes. (orig.)
Casimir-Polder Potential in Thermal Non-Equilibrium
Ellingsen, Simen Å; Buhmann, Stefan Y; Scheel, Stefan
2009-01-01
Different non-equilibrium situations have recently been considered when studying the thermal Casimir--Polder interaction with a body. We show that the Keldysh Green function method provides a very general common framework for such studies where non-equilibrium of either the atom or the body with the environment can be accounted for. We apply the results to the case of ground state polar molecules out of equilibrium with their environment, observing several striking effects. We consider thermal Casimir--Polder potentials in planar configurations, and new results for a molecule in a cylindrical cavity are reported, showing similar characteristic behaviour as found in planar geometry.
Canonical realization of Bondi-Metzner-Sachs symmetry: Quadratic Casimir
Gomis, Joaquim; Longhi, Giorgio
2016-01-01
We study the canonical realization of Bondi-Metzner-Sacks symmetry for a massive scalar field introduced by Longhi and Materassi [J. Math. Phys. 40, 480 (1999)]. We construct an invariant scalar product for the generalized momenta. As a consequence we introduce a quadratic Casimir with the supertranslations.
Dynamical Casimir Effect for Two Oscillating Mirrors in 3-D
Yuce, Cem
2008-01-01
The generation of photons in a three dimensional rectangular cavity with two moving boundaries is studied by using the Multiple Scale Analysis (MSA). It is shown that number of photons are enhanced for the cavity whose walls oscillate symmetrically with respect to the center of the cavity. The non-stationary Casimir effect is also discussed for the cavity which oscillates as a whole.
A special kind of Casimir plates for making exotic matter
Mansooryar, M
2003-01-01
Herein a process of suitable extraction of energy from vacuum is introduced. By followung Ridgely's idea[1], it is proposed some molecular fine-scale plates. Then some properties of them are considered. In fact Casimir effect is viewed in engineering manner. The introduced plates may be applied for support of traversable wormholes (TWs) & warp drives (WDs).
Materials Bound by Non-Chemical Forces: External Fields and the Quantum Vacuum
Swain, John; Srivastava, Yogendra
2014-01-01
We discuss materials which owe their stability to external fields. These include: 1) external electric or magnetic fields, and 2) quantum vacuum fluctuations in these fields induced by suitable boundary conditions (the Casimir effect). Instances of the first case include the floating water bridge and ferrofluids in magnetic fields. An example of the second case is taken from biology where the Casimir effect provides an explanation of the formation of stacked aggregations or "rouleaux" by negatively charged red blood cells. We show how the interplay between electrical and Casimir forces can be used to drive self-assembly of nano-structured materials, and could be generalized both as a probe of Casimir forces and as a means of manufacturing nanoscale structures. Interestingly, all the cases discussed involve the generation of the somewhat exotic negative pressures. We note that very little is known about the phase diagrams of most materials in the presence of external fields other than those represented by the ...
Barton, Gabriel; Dodonov, Victor V.; Man'ko, Vladimir I.
2004-05-01
The past few years have seen a growing interest in quantum mechanical systems with moving boundaries. One of its manifestations was the First International Workshop on Problems with Moving Boundaries organized by Professor J Dittrich in Prague in October 2003. Another event in this series will be the (first) International Workshop on the Dynamical Casimir Effect in Padua in June 2004, organized by Professor G Carugno (see webpage www.pd.infn.it/casimir/ for details). As Guest Editors we invite researchers working in any area related to moving boundaries to contribute to a Topical Issue of Journal of Optics B: Quantum and Semiclassical Optics on the nonstationary Casimir effect and quantum systems with moving boundaries. Our intention is to cover a wide range of topics. In particular, we envisage possible contributions in the following areas: Theoretical and experimental studies on quantum fields in cavities with moving boundaries and time-dependent media. This area includes, in particular, various manifestations of the nonstationary (dynamical) Casimir effect, such as creation of quanta and modifications of Casimir force due to the motion of boundaries. Other relevant subjects are: generation and evolution of nonclassical states of fields and moving mirrors; interaction between quantized fields and atoms in cavities with moving boundaries; decoherence and entanglement due to the motion of boundaries; field quantization in nonideal cavities with moving boundaries taking into account losses and dispersion; nano-devices with moving boundaries. Quantum particles in domains confined with moving boundaries. This area includes: new exact and approximate solutions of the evolution equations (Schrödinger, Klein-Gordon, Dirac, Fokker-Planck, etc); quantum carpets and revivals; escape and tunnelling through moving barriers; evolution of quantum packets in the presence of moving boundaries; ultracold atoms (ions) in traps with moving boundaries. The topical issue is scheduled
Thermal Casimir-Polder shifts in Rydberg atoms near metallic surfaces
Crosse, J A; Clements, Kate; Buhmann, Stefan Y; Scheel, Stefan
2010-01-01
The Casimir-Polder (CP) potential and transition rates of a Rydberg atom above a plane metal surface at finite temperature are discussed. As an example, the CP potential and transition rates of a rubidium atom above a copper surface at room temperature is computed. Close to the surface we show that the quadrupole correction to the force is significant and increases with increasing principal quantum number n. For both the CP potential and decay rates one finds that the dominant contribution comes from the longest wavelength transition and the potential is independent of temperature. We provide explicit scaling laws for potential and decay rates as functions of atom-surface distance and principal quantum number of the initial Rydberg state.
The Casimir effect with quantized charged spinor matter in background magnetic field
Sitenko, Yu A
2014-01-01
We study the influence of a background uniform magnetic field and boundary conditions on the vacuum of a quantized charged spinor matter field confined between two parallel neutral plates; the magnetic field is directed orthogonally to the plates. The admissible set of boundary conditions at the plates is determined by the requirement that the Dirac hamiltonian operator be self-adjoint. It is shown that, in the case of a sufficiently strong magnetic field and a sufficiently large separation of the plates, the Casimir force is repulsive, being independent of the choice of a boundary condition, as well as of the distance between the plates. The detection of this effect seems to be feasible in a foreseen future.
Casimir micro-sphere diclusters and three-body effects in fluids
Varela, Jaime; McCauley, Alexander P; Johnson, Steven G
2010-01-01
Our previous article [Phys. Rev. Lett. 104, 060401 (2010)] predicted that Casimir forces induced by the material-dispersion properties of certain dielectrics can give rise to stable configurations of objects. This phenomenon was illustrated via a dicluster configuration of non-touching objects consisting of two spheres immersed in a fluid and suspended against gravity above a plate. Here, we examine these predictions from the perspective of a practical experiment and consider the influence of non-additive, three-body, and nonzero-temperature effects on the stability of the two spheres. We conclude that the presence of Brownian motion reduces the set of experimentally realizable silicon/teflon spherical diclusters to those consisting of layered micro-spheres, such as the hollow- core (spherical shells) considered here.
Dynamics of the Vacuum and Casimir Analogs to the Hydrogen Atom
White, Harold; Vera, Jerry; Bailey, Paul; March, Paul; Lawrence, Tim; Sylvester, Andre; Brady, David
2015-01-01
This paper will discuss the current viewpoint of the vacuum state and explore the idea of a "natural" vacuum as opposed to immutable, non-degradable vacuum. This concept will be explored for all primary quantum numbers to show consistency with observation at the level of Bohr theory. A comparison with the Casimir force per unit area will be made, and an explicit function for the spatial variation of the vacuum density around the atomic nucleus will be derived. This explicit function will be numerically modeled using the industry multi-physics tool, COMSOL(trademark), and the eigenfrequencies for the n = 1 to n = 7 states will be found and compared to expectation.
Van der Waals forces in pNRQED
Energy Technology Data Exchange (ETDEWEB)
Shtabovenko, Vladyslav [Physik-Department, Technische Universität München, James-Franck-Str. 1, 85748 Garching (Germany)
2016-01-22
We report on the calculation of electromagnetic van der Waals forces [1] between two hydrogen atoms using non-relativistic effective field theories (EFTs) of QED for large and small momentum transfers with respect to the intrinsic energy scale of the hydrogen atom. Our results reproduce the well known London and Casimir-Polder forces.
Tomas, M S
2005-01-01
We discuss some implications of a very recently obtained result for the force on a slab in a planar cavity based on the calculation of the vacuum Lorentz force [C. Raabe and D.-G. Welsch, Phys. Rev. A 71, 013814 (2005)]. We demonstrate that, according to this formula, the total force on the slab consists of a medium-screened Casimir force and, in addition to it, a medium-assisted force. The sign of of the medium-assisted force is determined solely by the properties of the cavity mirrors. In the Lifshitz configuration, this force is proportional to 1/d at small distances and is very small compared with the corresponding van der Waals force. At large distances, however, it is proportional to 1/d^4 and is comparable with the Casimir force, especially for denser media. The exponents in these power laws decrease by 1 in the case of a thin slab. The formula for the medium-assisted force also describes the force on a layer of the cavity medium, which has similar properties. For dilute media, it implies an atom-mirro...
Casimir entropy and internal energy of the objects in fluctuating scalar and electromagnetic fields
Jafari, Marjan
2016-01-01
Casimir entropy is an important aspect of casimir effect.In this paper,we employ the path integral method to derive the total relation for casimir entropy and internal energy of arbitrary shaped objects in the presence of two,three and four dimensions scalar fields and electromagnetic field.We obtain the casimir entropy and internal energy of two nanoribbon immersed in scalar field and two nanospheres immersed in scalar field and electromagnetic field.The casmir entropy of two nanospheres immersed in the electromagnetic field in small interval of temperature variations,shown a different behavior.
Energy Technology Data Exchange (ETDEWEB)
Soroush, R [Electronics Engineering Department, Islamic Azad University, Lahijan Branch, Lahijan (Iran, Islamic Republic of); Koochi, A; Haddadpour, H [Department of Aerospace Engineering, and Center of Excellence in Aerospace Systems, Sharif University of Technology, Azadi Avenue, PO Box 11165-8639, Tehran (Iran, Islamic Republic of); Kazemi, A S [School of Physics and Center for Solid State Research, Damghan University for Basic Sciences, PO Box 367164-167, Damghan (Iran, Islamic Republic of); Noghrehabadi, A [Department of Mechanical Engineering, Shahid Chamran University, PO Box 613574-333, Ahvaz (Iran, Islamic Republic of); Abadyan, M, E-mail: A.R.Noghrehabadi@scu.ac.i, E-mail: Abadyan@yahoo.co [Mechanical Engineering Group, Islamic Azad University Ramsar Branch, Ramsar Center, Ramsar (Iran, Islamic Republic of)
2010-10-15
This paper investigates the effect of dispersion (van der Waals and Casimir) forces on the pull-in instability of cantilever nano-actuators by considering their range of application. Adomian decomposition is introduced to obtain an analytical solution of the distributed parameter model. Dispersion forces decrease the pull-in deflection and voltage of a nano-actuator. However, the fringing field increases the pull-in deflection while decreasing the pull-in voltage of the actuator. The minimum initial gap and the detachment length of the actuator that does not stick to the substrate due to van der Waals and Casimir attractions were determined. Furthermore, the proposed approach is capable of determining the stress distribution of the actuator at the onset of instability. It is seen that Casimir and van der Waals attractions effectively reduce the maximum value of stress resultants at the onset of instability. The results indicate that Adomian decomposition is a reliable method for simulating nano-structures at submicrometer ranges.
Keivani, Maryam; Mardaneh, Mohamadreza; Koochi, Ali; Rezaei, Morteza; Abadyan, Mohamadreza
2016-02-01
Herein, the dynamic pull-in instability of cantilever nanoactuator fabricated from conductive cylindrical nanowire with circular cross-section is studied under the presence of Casimir force. The Gurtin-Murdoch surface elasticity in combination with the couple stress theory is employed to incorporate the coupled effects of surface energy and size phenomenon. Using Green-Lagrange strain, the higher order surface stress components are incorporated in the governing equation. The Dirichlet mode is considered and an asymptotic solution, based on the path integral approach, is applied to consider the effect of the Casimir attraction. Furthermore, the influence of structural damping is considered in the model. The nonlinear governing equation is solved using analytical reduced order method (ROM). The effects of various parameters on the dynamic pull-in parameters, phase planes and stability threshold of the actuator are demonstrated.
Casimir, Gravitational and Neutron Tests of Dark Energy
Brax, Philippe
2014-01-01
We investigate laboratory tests of dark energy theories which modify gravity in a way generalising the inverse power law chameleon models. We make use of the tomographic description of such theories which captures $f(R)$ models in the large curvature limit, the dilaton and the symmetron. We consider their effects in various experiments where the presence of a new scalar interaction may be uncovered. More precisely, we focus on the Casimir, Eot-wash and neutron experiments. We show that dilatons, symmetrons and generalised chameleon models are efficiently testable in the laboratory. For generalised chameleons, we revise their status in the light of forthcoming Casimir experiments like CANNEX in Amsterdam and show that they are within reach of detection.
Casimir Energy of a Semi-Circular Infinite Cylinder
Nesterenko, V V; Scarpetta, G
2001-01-01
The Casimir energy of a semi-circular cylindrical shell is calculated by making use of the zeta function technique. This shell is obtained by crossing an infinite circular cylindrical shell by a plane passing through the symmetry axes of the cylinder and by considering only a half of this configuration. All the surfaces, including the cutting plane, are assumed to be perfectly conducting. The zeta functions for scalar massless fields obeying the Dirichlet and Neumann boundary conditions on the semi-circular cylinder are constructed exactly. The sum of these zeta functions gives the zeta function for electromagnetic field in question. The relevant plane problem is considered also. In all the cases the final expressions for the corresponding Casimir energies contain the pole contributions. This implies that further renormalization is needed in order for the finite physical values for vacuum energy to be obtained for given boundary conditions.
Casimir energy of a semi-circular infinite cylinder
Nesterenko, V. V.; Lambiase, G.; Scarpetta, G.
2001-05-01
The Casimir energy of a semi-circular cylindrical shell is calculated by making use of the zeta function technique. This shell is obtained by crossing an infinite circular cylindrical shell by a plane passing through the symmetry axes of the cylinder and by considering only half of this configuration. All the surfaces, including the cutting plane, are assumed to be perfectly conducting. The zeta functions for scalar massless fields obeying the Dirichlet and Neumann boundary conditions on the semi-circular cylinder are constructed exactly. The sum of these zeta functions gives the zeta function for the electromagnetic field in question. The relevant plane problem is considered also. In all the cases the final expressions for the corresponding Casimir energies contain the pole contributions which are the consequence of the edges or corners in the boundaries. This implies that further renormalization is needed in order for the finite physical values for vacuum energy to be obtained for given boundary conditions.
On the Casimir Energy of Frequency Dependent Interactions
Graham, N; Weigel, H
2014-01-01
Vacuum polarization (or Casimir) energies can be straightforwardly computed from scattering data for static field configurations whose interactions with the fluctuating field are frequency independent. In effective theories, however,such interactions are typically frequency dependent. As a consequence, the relationship between scattering data and the Green's function is modified, which may or may not induce additional contributions to the vacuum polarization energy. We discuss several examples that naturally include frequency dependent interactions: (i) scalar electrodynamics with a static background potential, (ii) an effective theory that emerges from integrating out a heavy degree of freedom, and (iii) quantum electrodynamics coupled to a frequency dependent dielectric material. In the latter case, we argue that introducing dissipation as required by the Kramers-Kronig relations requires the consideration of the Casimir energy within a statistical mechanics formalism, while in the absence of dissipation we...
Casimir Self-Entropy of an Electromagnetic Thin Sheet
Li, Yang; Kalauni, Pushpa; Parashar, Prachi
2016-01-01
Casimir entropies due to quantum fluctuations in the interaction between electrical bodies can often be negative, either caused by dissipation or by geometry. Although generally such entropies vanish at zero temperature, consistent with the third law of thermodynamics (the Nernst heat theorem), there is a region in the space of temperature and separation between the bodies where negative entropy occurs, while positive interaction entropies arise for large distances or temperatures. Systematic studies on this phenomenon in the Casimir-Polder interaction between a polarizable nanoparticle or atom and a conducting plate in the dipole approximation have been given recently. Since the total entropy should be positive according to the second law of thermodynamics, we expect that the self-entropy of the bodies would be sufficiently positive as to overwhelm the negative interaction entropy. This expectation, however, has not been explicitly verified. Here we compute the self-entropy of an electromagnetic $\\delta$-fun...
Symmetries and casimir of an extended classical long wave system
Indian Academy of Sciences (India)
K M Tamizhmani; R Ilangovane; B Dubrovin
2013-04-01
In this paper, we derive Lie point, generalized, master and time-dependent symmetries of a dispersionless equation, which is an extension of a classical long wave system. This equation also admits an infinite-dimensional Lie algebraic structure of Virasoro-type, as in the dispersive integrable systems. We discuss the construction of a sequence of negative ranking symmetries through the property of uniformity in rank. More interestingly, we obtain the conserved quantities directly from the casimir of Poisson pencil.
Van der Waals and Casimir-Polder interactions between neutrons
Directory of Open Access Journals (Sweden)
Babb James F.
2016-01-01
Full Text Available We investigate the van der Waals interaction between neutrons using the theory of Casimir and Polder, wherein the potential for asymptotically large separations falls off as the inverse seventh power, and compare it to the similar interaction between a neutron and a proton, for which the asymptotic interaction falls off as the inverse fourth power. Modifications of the formalism to extend the validity to smaller separations using dynamic electric and magnetic dipole polarizability data are discussed.
On the static Casimir effect with parity-breaking mirrors
Fosco, C D
2016-01-01
We study the Casimir interaction energy due to the vacuum fluctuations of the Electromagnetic (EM) field in the presence of two mirrors, described by $2+1$-dimensional, generally nonlocal actions, which may contain both parity-conserving and parity-breaking terms. We compare the results with the ones corresponding to Chern-Simons boundary conditions, and evaluate the interaction energy for several particular situations.
Van der Waals and Casimir-Polder interactions between neutrons
Babb, James F.; Hussein, Mahir S.
2016-03-01
We investigate the van der Waals interaction between neutrons using the theory of Casimir and Polder, wherein the potential for asymptotically large separations falls off as the inverse seventh power, and compare it to the similar interaction between a neutron and a proton, for which the asymptotic interaction falls off as the inverse fourth power. Modifications of the formalism to extend the validity to smaller separations using dynamic electric and magnetic dipole polarizability data are discussed.
Van der Waals and Casimir-Polder interactions between neutrons
Babb James F.; Hussein Mahir S.
2016-01-01
We investigate the van der Waals interaction between neutrons using the theory of Casimir and Polder, wherein the potential for asymptotically large separations falls off as the inverse seventh power, and compare it to the similar interaction between a neutron and a proton, for which the asymptotic interaction falls off as the inverse fourth power. Modifications of the formalism to extend the validity to smaller separations using dynamic electric and magnetic dipole polarizability data are di...
van der Waals and Casimir-Polder interactions between neutrons
Babb, James F
2015-01-01
We investigate the van der Waals interaction between neutrons using the theory of Casimir and Polder, wherein the potential for asymptotically large separations falls off as the inverse seventh power, and compare it to the similar interaction between a neutron and a proton, for which the asymptotic interaction falls off as the inverse fourth power. Modifications of the formalism to extend the validity to smaller separations using dynamic electric and magnetic dipole polarizability data are discussed
Positive Casimir and Central Characters of Split Real Quantum Groups
Ip, Ivan Chi-Ho
2015-01-01
We describe the generalized Casimir operators and their actions on the positive representations $P_{\\lambda}$ of the modular double of split real quantum groups $U_{q\\tilde{q}}(g_R)$. We introduce the notion of virtual highest and lowest weights, and show that the central characters admit positive values for all parameters $\\lambda$. We show that their image defines a semi-algebraic region bounded by real points of the discriminant variety independent of $q$, and we discuss explicit examples ...
Thermal Casimir-Polder interaction of different atoms with graphene
Chaichian, M; Mostepanenko, V M; Tureanu, A
2012-01-01
The thermal correction to the energy of Casimir-Polder interaction of atoms with a suspended graphene membrane described by the Dirac model is investigated. We show that a major impact on the thermal correction is made by the size of the gap in the energy spectrum of graphene quasiparticles. Specifically, if the temperature is much smaller than the gap parameter (alternatively, larger or of the order of the gap parameter), the thermal correction is shown to be relatively small (alternatively, large). We have calculated the free energy of the thermal Casimir-Polder interaction of atoms of He, Na, Rb, and Cs with graphene described by both the hydrodynamic and Dirac models. It is shown that in exact computations using the Dirac model, one should use the polarization operator at nonzero temperature. The computational results for the Casimir-Polder free energy obtained in the framework of hydrodynamic model of graphene are several times larger than in the Dirac model within the separation region below 2$\\mu$m. We...
Casimir Effect at Finite Temperature in the Presence of Compactified Universal Extra Dimensions
Institute of Scientific and Technical Information of China (English)
CHENG Hong-Bo
2005-01-01
@@ We analyse the Casimir effect for parallel plates atfinite temperature in the presence of compactified universal extra dimensions and analytically show the thermal corrections to the effect in detail. The Casimir effect for different sizes of universal extra dimensions is investigated to test the five-dimensional Kaluza-Klein theory.
Casimir Effect for a Massless Spin-3/2 Field in Minkowski Spacetime
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The Casimir effect has been studied for various quantum fields in both flat and curved spacetimes. As a further step along this line, we provide an explicit derivation of Casimir effect for massless spin-3/2 field with periodic boundary condition imposed in four-dimensional Minkowski spacetime. The corresponding results with Dirichlet ard Neumann boundary conditions are also discussed.
Casimir bag energy in the stochastic approximation to the pure QCD vacuum
Fosco, C D
2007-01-01
We study the Casimir contribution to the bag energy coming from gluon field fluctuations, within the context of the stochastic vacuum model (SVM) of pure QCD. After formulating the problem in terms of the generating functional of field strength cumulants, we argue that the resulting predictions about the Casimir energy are compatible with the phenomenologically required bag energy term.
Symmetric ordering effect on Casimir energy in $\\kappa-$Minkowski spacetime
Kim, Hyeong-Chan; Yee, Jae Hyung
2008-01-01
We present the Casimir energy of spherical shell, for the symmetrically deformed scalar field in $\\kappa$-Minkowski space-time, satisfying Dirichlet boundary condition. The Casimir energy shows the particle anti-particle symmetry contrary to the asymmetrically deformed case. In addition, the deformation effect starts from $O(1/\\kappa)$ term unlike in the parallel plates.
Casimir-Foucault interaction: Free energy and entropy at low temperature
Intravaia, F; Henkel, C
2010-01-01
It was recently found that thermodynamic anomalies which arise in the Casimir effect between metals described by the Drude model can be attributed to the interaction of fluctuating Foucault (or eddy) currents [Phys. Rev. Lett. 103, 130405 (2009)]. We show explicitly that the two leading terms of the low-temperature correction to the Casimir free energy of interaction between two plates, are identical to those pertaining to the Foucault current interaction alone, up to a correction which is very small for good metals. Moreover, a mode density along real frequencies is introduced, showing that the Casimir free energy, as given by the Lifshitz theory, separates in a natural manner in contributions from eddy currents and propagating cavity modes, respectively. The latter have long been known to be of little importance to the low-temperature Casimir anomalies. This convincingly demonstrates that eddy current modes are responsible for the large temperature correction to the Casimir effect between Drude metals, pred...
Casimir interaction between spheres in $\\boldsymbol{(D+1)}$-dimensional Minkowski spacetime
Teo, L P
2014-01-01
We consider the Casimir interaction between two spheres in $(D+1)$-dimensional Minkowski spacetime due to the vacuum fluctuations of scalar fields. We consider combinations of Dirichlet and Neumann boundary conditions. The TGTG formula of the Casimir interaction energy is derived. The computations of the T matrices of the two spheres are straightforward. To compute the two G matrices, known as translation matrices, which relate the hyper-spherical waves in two spherical coordinate frames differ by a translation, we generalize the operator approach employed in [IEEE Trans. Antennas Propag. \\textbf{36}, 1078 (1988)]. The result is expressed in terms of an integral over Gegenbauer polynomials. Using our expression for the Casimir interaction energy, we derive the large separation and small separation asymptotic expansions of the Casimir interaction energy. In the large separation regime, we find that the Casimir interaction energy is of order $L^{-2D+3}$, $L^{-2D+1}$ and $L^{-2D-1}$ respectively for Dirichlet-Di...
Test of non-Newtonian gravitational force at micrometer range
Luo, Pengshun; Guan, Shengguo; Wu, Wenjie; Tian, Zhaoyang; Yang, Shanqing; Shao, Chenggang; Luo, Jun
2016-01-01
We report an experimental test of non-Newtonian gravitational forces at mi- crometer range. To experimentally subtract off the Casimir force and the electrostatic force background, differential force measurements were performed by sensing the lateral force between a gold sphere and a density modulated source mass using a soft cantilever. The current sensitivity is limited by the patch electrostatic force, which is further improved by two dimensional (2D) force mapping. The preliminary result sets a model independent constraint on the Yukawa type force at this range.
Kappa-deformed quantum field theory and Casimir effect
Cougo-Pinto, M. V.; C. Farina; Mendes, J. F. M.
2003-01-01
We consider the quantization of a scalar kappa-deformed field up to the point of obtaining an expression for its vacuum energy. The expression is given by the half sum of the field frequencies, as in the non-deformed case, but with the frequencies obeying the kappa-deformed dispersion relation. We consider a set of kappa-deformed Maxwell equations and show that for the purpose of calculating the Casimir energy the Maxwell field, as in the non-deformed case, behaves as a pair of scalar fields....
Generalized Bogoliubov Transformation for Confined Fields Applications in Casimir Effect
Silva, J C; Neto, A M; Santana, A E
2002-01-01
The Bogoliubov transformation in thermofield dynamics, an operator formalism for the finite-temperature quantum-field theory, is generalized to describe a field in arbitrary confined regions of space and time. Starting with the scalar field, the approach is extended to the electromagnetic field and the energy-momentum tensor is written via the Bogoliubov transformation. In this context, the Casimir effect is calculated for zero and non-zero temperature, and therefore it can be considered as a vacuum condensation effect of the electromagnetic field. This aspect opens an interesting perspective for using this procedure as an effective scheme for calculations in the studies of confined fields, including the interacting fields.
Casimir Effect for Gauge Scalars: The Kalb-Ramond Case
Barone, F A; Helayel-Neto, J A
2005-01-01
In this work we calculate the functional generator of the Green's functions of the Kalb-Ramond field in 3+1 dimensions. We also calculate the functional generator, and corresponding Casimir energy, of the same field when it is submitted to boundary conditions on two parallel planes. The boundary conditions we consider can be interpreted as a kind of conducting planes for the field in compearing with the Maxweel case. We compare our result with the standard ones for the scalar and Maxwell fields.
What Casimir Energy can suggest about Space Time Foam?
Garattini, R
2001-01-01
In the context of a model of space-time foam, made by $N$ wormholes we discuss the possibility of having a foam formed by different configurations. An equivalence between Schwarzschild and Schwarzschild-Anti-de Sitter wormholes in terms of Casimir energy is shown. An argument to discriminate which configuration could represent a foamy vacuum coming from Schwarzschild black hole transition frequencies is used. The case of a positive cosmological constant is also discussed. Finally, a discussion involving charged wormholes leads to the conclusion that they cannot be used to represent a ground state of the foamy type.
Using boundary methods to compute the Casimir energy
Lombardo, F C; Villar, P I
2010-01-01
We discuss new approaches to compute numerically the Casimir interaction energy for waveguides of arbitrary section, based on the boundary methods traditionally used to compute eigenvalues of the 2D Helmholtz equation. These methods are combined with the Cauchy's theorem in order to perform the sum over modes. As an illustration, we describe a point-matching technique to compute the vacuum energy for waveguides containing media with different permittivities. We present explicit numerical evaluations for perfect conducting surfaces in the case of concentric corrugated cylinders and a circular cylinder inside an elliptic one.
Dunckle, Christopher Gregory
Time Reversal can be used to time reverse and propagate the measured scattered wave- forms to a point in both time and space, ideally to a delta function delta( r⃗ )delta(t). This is commonly referred to as time reversal focusing and has led to time reversal being applied in a wide variety of fields such as medicine, communications, nondestructive evaluation (NDE), and seismology. In practice, time reversal is not optimal for generating a delta function focus if certain conditions are not upheld. For time reversal to work perfectly, the following four conditions must be present: (1) one must record for an infinitely long period of time; (2) Green's functions must be assumed to contain infinite bandwidth; (3) attenuation must be absent within the medium; and (4) one must have full coverage of the wavefield. Due to the need for these conditions, much research is being carried out in order to enhance the time reversal process in practice. We introduce deconvolution, a simple and robust approach, in order to calculate an optimal signal for back propagation designed to give an improved focus. We demonstrate experimentally that deconvolution is able to dramatically improve the temporal focus com- pared to time reversal. Through a joint project with Los Alamos National Laboratory, we compared time reversal to deconvolution. The results showed that deconvolution was able to dramatically improve the temporal focus for a source and a receiver which were both located on the surface of our object. We then continued our experimental studies of deconvolution by doing a joint project with researcher Dr. Ernst Niederleithinger from the Federal Institute for Materials Research and Testing (BAM). For this experiment, we placed multiple sources within a concrete block and recorded the source wavefields on the surface with a single re- ceiver. This experiment was designed to further test the robust nature of deconvolution and compare its temporal focusing capability to that of time reversal. All of these experimental studies show that deconvolution was able to improve the temporal focus compared to time reversal. We continued our comparison study between time reversal and deconvolution and demon- strated theoretically, experimentally, and numerically that deconvolution also improves spa- tial focusing. We give a proof explaining why one would expect improved spatial focusing when there is improved temporal focusing for both a acoustic and elastic media. We then demonstrate in our experiments the improved spatial focus achieved using deconvolution by scanning around the source location with a laser vibrometer at the time of focus for an acoustic case. Finally, we use deconvolution to locate synthetic microseismic events to prove numerically that improved temporal focusing leads to improved spatial focusing for both acoustic and elastic media.
Effect of intermolecular force on the static/dynamic behaviour of M/NEM devices
Kim, Namjung; Aluru, N. R.
2014-12-01
Advances made in the fabrication of micro/nano-electromechanical (M/NEM) devices over the last ten years necessitate the understanding of the attractive force that arises from quantum fluctuations (generally referred to as Casimir effects) [Casimir H B G 1948 Proc. K. Ned. Akad. Wet. 51 793]. The fundamental mechanisms underlying quantum fluctuations have been actively investigated through various theoretical and experimental approaches. However, the effect of the force on M/NEM devices has not been fully understood yet, especially in the transition region involving gaps ranging from 10 nm to 1 μm, due to the complexity of the force. Here, we numerically calculate the Casimir effects in M/NEM devices by using the Lifshitz formula, the general expression for the Casimir effects [Lifshitz E 1956 Sov. Phys. JETP 2 73]. Since the Casimir effects are highly dependent on the permittivity of the materials, the Kramer-Kronig relation [Landau L D, Lifshitz E M and Pitaevskii L P 1984 Electrodynamics of Continuous Media (New York: Pergamon Press)] and the optical data for metals and dielectrics are used in order to obtain the permittivity. Several simplified models for the permittivity of the materials, such as the Drude and Lorentz models [Jackson J D 1975 Classical Electrodynamics (New York: Wiley)], are also used to extrapolate the optical data. Important characteristic values of M/NEM devices, such as the pull-in voltage, pull-in gap, detachment length, etc, are calculated for devices operating in the transition region. Our results show that accurate predictions for the pull-in behaviour are possible when the Lifshitz formula is used instead of the idealized expressions for Casimir effects. We expand this study into the dynamics of M/NEM devices, so that the time and frequency response of M/NEM devices with Casimir effects can be explored.
Effect of intermolecular force on the static/dynamic behaviour of M/NEM devices.
Kim, Namjung; Aluru, N R
2014-12-01
Advances made in the fabrication of micro/nano-electromechanical (M/NEM) devices over the last ten years necessitate the understanding of the attractive force that arises from quantum fluctuations (generally referred to as Casimir effects) [Casimir H B G 1948 Proc. K. Ned. Akad. Wet. 51 793]. The fundamental mechanisms underlying quantum fluctuations have been actively investigated through various theoretical and experimental approaches. However, the effect of the force on M/NEM devices has not been fully understood yet, especially in the transition region involving gaps ranging from 10 nm to 1 μm, due to the complexity of the force. Here, we numerically calculate the Casimir effects in M/NEM devices by using the Lifshitz formula, the general expression for the Casimir effects [Lifshitz E 1956 Sov. Phys. JETP 2 73]. Since the Casimir effects are highly dependent on the permittivity of the materials, the Kramer-Kronig relation [Landau L D, Lifshitz E M and Pitaevskii L P 1984 Electrodynamics of Continuous Media (New York: Pergamon Press)] and the optical data for metals and dielectrics are used in order to obtain the permittivity. Several simplified models for the permittivity of the materials, such as the Drude and Lorentz models [Jackson J D 1975 Classical Electrodynamics (New York: Wiley)], are also used to extrapolate the optical data. Important characteristic values of M/NEM devices, such as the pull-in voltage, pull-in gap, detachment length, etc, are calculated for devices operating in the transition region. Our results show that accurate predictions for the pull-in behaviour are possible when the Lifshitz formula is used instead of the idealized expressions for Casimir effects. We expand this study into the dynamics of M/NEM devices, so that the time and frequency response of M/NEM devices with Casimir effects can be explored.
Large-n approach to thermodynamic Casimir effects in slabs with free surfaces
Diehl, H. W.; Grüneberg, Daniel; Hasenbusch, Martin; Hucht, Alfred; Rutkevich, Sergei B.; Schmidt, Felix M.
2014-06-01
The classical n-vector ϕ4 model with O (n) symmetrical Hamiltonian H is considered in a ∞2×L slab geometry bounded by a pair of parallel free surface planes at separation L. Standard quadratic boundary terms implying Robin boundary conditions are included in H. The temperature-dependent scaling functions of the excess free energy and the thermodynamic Casimir force are computed in the large-n limit for temperatures T at, above, and below the bulk critical temperature Tc. Their n =∞ limits can be expressed exactly in terms of the spectrum and eigenfunctions of a self-consistent one-dimensional Schrödinger equation. This equation is solved by numerical means for two distinct discretized versions of the model: in the first ("model A"), only the coordinate z across the slab is discretized and the integrations over momenta conjugate to the lateral coordinates are regularized dimensionally; in the second ("model B"), a simple cubic lattice with periodic boundary conditions along the lateral directions is used. Renormalization-group ideas are invoked to show that, in addition to corrections to scaling ∝L-1, anomalous ones ∝L-1lnL should occur. They can be considerably decreased by taking an appropriate g →∞ (Tc→∞) limit of the ϕ4 interaction constant g. Depending on the model A or B, they can be absorbed completely or to a large extent in an effective thickness Leff=L+δL. Excellent data collapses and consistent high-precision results for both models are obtained. The approach to the low-temperature Goldstone values of the scaling functions is shown to involve logarithmic anomalies. The scaling functions exhibit all qualitative features seen in experiments on the thinning of wetting layers of 4He and Monte Carlo simulations of XY models, including a pronounced minimum of the Casimir force below Tc. The results are in conformity with various analytically known exact properties of the scaling functions.
Weak dispersive forces between glass and gold macroscopic surfaces in alcohols
van Zwol, P. J.; Palasantzas, G.; DeHosson, J. Th. M.
2009-01-01
In this work we concentrate on an experimental validation of the Lifshitz theory for the van der Waals and the Casimir forces in gold-alcohol-glass systems. From this theory weak dispersive forces are predicted when the dielectric properties of the intervening medium become comparable to one of the
On the Casimir interaction between holes
Kabat, Daniel; Nair, V P
2010-01-01
We study the leading long-distance attractive force between two holes in a plate arising from a scalar field with Dirichlet boundary conditions on the plate. We use a formalism in which the interaction is governed by a non-local field theory which lives on the two holes. The interaction energy is proportional to Q_1 Q_2/r^7 at large separation r, where Q_1 and Q_2 are certain charges associated with the holes. We compute these charges for round and rectangular holes. We show that the 1/r^7 behavior is universal for separations large compared to the linear dimensions of the holes, irrespective of the spin or interactions of the bosonic field. We also study the interaction between two long thin slits, for which the energy falls off as 1/r^6.
Casimir Theory of the Relativistic Composite String Revisited
Brevik, Iver
2012-01-01
This is an updated review article on the Casimir energy at zero and finite temperature for the transverse oscillations of a piecewise uniform closed string. We make use of three different regularizations: the cutoff method, the complex contour integration method, and the zeta-function method. The string model is relativistic, in the sense that the velocity of sound is for each string piece set equal to the velocity of light. In this sense the theory is analogous to the electromagnetic theory in a dielectric medium in which the product of permittivity and permeability is equal to unity (an isorefractive medium). We demonstrate how the formalism works for a two-piece string, and for a 2N-piece string, and show how in the latter case a compact recursion relation serves to facilitate the formalism considerably. The Casimir energy turns out to be negative, and the more so the larger the number of pieces in the string. The two-piece string is quantized in D-dimensional spacetime, in the limit when the ratio between...
Institute of Scientific and Technical Information of China (English)
葛飞飞; 翟向华
2012-01-01
研究了满足螺旋边界条件的额外维存在时的平行板标量场Casimir效应.利用Zeta函数正则化方法,得到了用第二类变形Bessel函数表示的Casimir力.发现Casimir力总是吸引力,但是对于相同尺度的螺旋结构参数和平板间的距离,与不存在额外维的情形相比,平板间Casimir力的大小降低了一个数量级.螺旋结构参数越小,Casimir力的大小降低越多.%In this paper,we consider the scalar Casimir effect for parallel plates in the presence of extra dimensions with helix boundary conditions.Using zeta function regularization technique,we get the Casimir pressure explicitly expressed by the modified Bessel function of the second kind.We find the Casimir force is always attractive but for the same magnitude of the helix parameter as the parallel separation,the magnitude of the force between the parallel plates decreases by one order of magnitude.The smaller the helix parameter compared to the plate separation,the more magnitudes the force decreases.
Casimir Effect Near the Future Singularity in Kaluza Klein Viscous Cosmology
Khadekar, G. S.
2016-02-01
In this paper we investigate the analytical properties of the scalar expansion θ in the cosmic fluid close to the future singularity, when the fluid possesses a constant bulk viscosity ζ in the framework of Kaluza-Klein theory of gravitation. In addition, we assume the viscous cosmology theories in the sense that the Casimir contributions to the energy density and pressure are both proportional to 1/ a 4, where a being scale factor. We also worked out the series expansion for the scalar expansion θ under the condition that the Casimir influence is small. However, near to the big rip singularity the Casimir term has to fade away and we obtain the same singularity behavior for the scalar expansion θ, energy density ρ, the scale factor a as in the Casimir-free viscous case.
Scattering potentials with LS-terms from first-order Casimir operators
Energy Technology Data Exchange (ETDEWEB)
Levay, P. [Inst. of Phys., Tech. Univ. Budapest (Hungary)
1995-10-21
Using a first-order Casimir operator calculated in a non-standard realization for the so(3,1) algebra, we obtain a one-dimensional scattering problem with LS-type interaction terms. It is shown that for this realization the square of this operator can be expressed in terms of the usual quadratic Casimir. Due to this constraint the scattering states are completely specified by restricting the possible set of eigenvalues accordingly. The results show that the use of extra Casimir operators can provide additional insight into the group theoretical structure of the scattering problem. A generalization for the so(2n-1,1), n>2 case is also given. The underlying supersymmetry of the resulting Schrodinger equations is pointed out. The supersymmetric charge operators are related to our first-order Casimir operators. (author)
Casimir effects for classical and quantum liquids in slab geometry: A brief review
Energy Technology Data Exchange (ETDEWEB)
Biswas, Shyamal, E-mail: sbsp@uohyd.ac.in [School of Physics, University of Hyderabad, C.R. Rao Road, Gachibowli, Hyderabad-500046 (India)
2015-05-15
We analytically explore Casimir effects for confinement of classical and quantum fluctuations in slab (film) geometry (i) for classical (critical) fluctuations over {sup 4}He liquid around the λ point, and (ii) for quantum (phonon) fluctuations of Bogoliubov excitations over an interacting Bose-Einstein condensate. We also briefly review Casimir effects for confinement of quantum vacuum fluctuations confined to two plates of different geometries.
The quantum Casimir operators of U{sub q}(gl{sub n}) and their eigenvalues
Energy Technology Data Exchange (ETDEWEB)
Li Junbo, E-mail: sd_junbo@163.co [School of Mathematics and Statistics, University of Sydney, NSW 2006 (Australia) and School of Mathematics and Statistics, Changshu Institute of Technology, Changshu 215500 (China)
2010-08-27
We show that the quantum Casimir operators of the quantum linear group constructed in early work of Bracken, Gould and Zhang together with one obvious central element generate the entire center of U{sub q}(gl{sub n}). As a byproduct of the proof, we obtain intriguing new formulae for eigenvalues of these quantum Casimir operators, which are expressed in terms of the characters of a class of finite-dimensional irreducible representations of the classical general linear algebra.
Teo, L. P.
2013-01-01
We consider the finite temperature Casimir free energy acting on a spherical shell in (D+1)-dimensional Minkowski spacetime due to the vacuum fluctuations of scalar and electromagnetic fields. Dirichlet, Neumann, perfectly conducting and infinitely permeable boundary conditions are considered. The Casimir free energy is regularized using zeta functional regularization technique. To renormalize the Casimir free energy, we compute the heat kernel coefficients $c_n$, $0\\leq n\\leq D+1$, from the ...
Fermi, Davide
2015-01-01
This is the first one of a series of papers about zeta regularization of the divergences appearing in the vacuum expectation value (VEV) of several local and global observables in quantum field theory. More precisely we consider a quantized, neutral scalar field on a domain in any spatial dimension, with arbitrary boundary conditions and, possibly, in presence of an external classical potential. We analyze, in particular, the VEV of the stress-energy tensor, the corresponding boundary forces and the total energy, thus taking into account both local and global aspects of the Casimir effect. In comparison with the wide existing literature on these subjects, we try to develop a more systematic approach, allowing to treat specific configurations by mere application of a general machinery. The present Part I is mainly devoted to setting up this general framework; at the end of the paper, this is exemplified in a very simple case. In Parts II, III and IV we will consider more engaging applications, indicated in the...
A Gedanken spacecraft that operates using the quantum vacuum (Dynamic Casimir effect)
MacLay, G J; Forward, Robert L.
2003-01-01
Conventional rockets are not a suitable technology for deep space missions. Chemical rockets require a very large weight of propellant, travel very slowly compared to light speed, and require significant energy to maintain operation over periods of years. For example, the 722 kg Voyager spacecraft required 13,600 kg of propellant to launch and would take about 80,000 years to reach the nearest star, Proxima Centauri, about 4.3 light years away. There have been various attempts at developing ideas on which one might base a spacecraft that would permit deep space travel, such as spacewarps. In this paper we consider another suggestion from science fiction and explore how the quantum vacuum might be utilized in the creation of a novel spacecraft. The spacecraft is based on the dynamic Casimir effect, in which electromagnetic radiation is emitted when an uncharged mirror is properly accelerated in the vacuum. The radiative reaction produces a dissipative force on the mirror that tends to resist the acceleration o...
Local and Global Casimir Energies: Divergences, Renormalization, and the Coupling to Gravity
Milton, Kimball A
2010-01-01
From the beginning of the subject, calculations of quantum vacuum energies or Casimir energies have been plagued with two types of divergences: The total energy, which may be thought of as some sort of regularization of the zero-point energy, $\\sum\\frac12\\hbar\\omega$, seems manifestly divergent. And local energy densities, obtained from the vacuum expectation value of the energy-momentum tensor, $\\langle T_{00}\\rangle$, typically diverge near boundaries. The energy of interaction between distinct rigid bodies of whatever type is finite, corresponding to observable forces and torques between the bodies, which can be unambiguously calculated. The self-energy of a body is less well-defined, and suffers divergences which may or may not be removable. Some examples where a unique total self-stress may be evaluated include the perfectly conducting spherical shell first considered by Boyer, a perfectly conducting cylindrical shell, and dilute dielectric balls and cylinders. In these cases the finite part is unique, y...
Dynamical Casimir Effect in a Leaky Cavity at Finite Temperature
Schaller, G; Plunien, G; Soff, G
2002-01-01
The phenomenon of particle creation within an almost resonantly vibrating cavity with losses is investigated for the example of a massless scalar field at finite temperature. A leaky cavity is designed via the insertion of a dispersive mirror into a larger ideal cavity (the reservoir). In the case of parametric resonance the rotating wave approximation allows for the construction of an effective Hamiltonian. The number of produced particles is then calculated using response theory as well as a non-perturbative approach. In addition we study the associated master equation and briefly discuss the effects of detuning. The exponential growth of the particle numbers and the strong enhancement at finite temperatures found earlier for ideal cavities turn out to be essentially preserved. The relevance of the results for experimental tests of quantum radiation via the dynamical Casimir effect is addressed. Furthermore the generalization to the electromagnetic field is outlined.
Superconducting circuit boundary conditions and the Dynamical Casimir Effect
Doukas, Jason
2014-01-01
We study analytically the time-dependent boundary conditions of superconducting microwave circuit experiments in the high plasma frequency limit, in which the conditions are Robin-type and relate the value of the field to the spatial derivative of the field. We solve the field evolution explicitly for boundary condition modulations that are small in magnitude but may have arbitrary time dependence, both for a half-open waveguide and for a closed waveguide with two independently adjustable boundaries. The correspondence between the microwave Robin boundary conditions and the mechanically-moving Dirichlet boundary conditions of the Dynamical Casimir Effect is shown to break down at high field frequencies, approximately one order of magnitude above the frequencies probed in the 2011 experiment of Wilson et al. Our results bound the parameter regime in which a microwave circuit can be used to model relativistic effects in a mechanically-moving cavity, and they show that beyond this parameter regime moving mirrors...
Inhibition of the dynamical Casimir effect with Robin boundary conditions
Rego, Andreson L C; Farina, C; Alves, Danilo T; 10.1103/PhysRevD.87.045024
2013-01-01
We consider a real massless scalar field in 3+1 dimensions satisfying a Robin boundary condition at a nonrelativistic moving mirror. Considering vacuum as the initial field state, we compute explicitly the number of particles created per unit frequency and per unit solid angle, exhibiting in this way the angular dependence of the spectral distribution. The well known cases of Dirichlet and Neumann boundary conditions may be reobtained as particular cases from our results. We show that the particle creation rate can be considerably reduced (with respect to the Dirichlet and Neumann cases) for particular values of the Robin parameter. Our results extend for 3+1 dimensions previous results found in the literature for 1+1 dimensions. Further, we also show that this inhibition of the dynamical Casimir effect occurs for different angles of particle emission.
Strongly Interacting Fermions and Phases of the Casimir Effect
Flachi, Antonino
2013-01-01
With the intent of exploring how the interplay between boundary effects and chiral symmetry breaking may alter the thermodynamical behavior of a system of strongly interacting fermions, we study the Casimir effect for the set-up of two parallel layers using a four-fermion effective field theory at zero density. This system reveals a number of interesting features. While for infinitely large separation (no boundaries), chiral symmetry is broken/restored via a second order phase transition, in the opposite case of small (and, in general, finite) separation the transition becomes first order, rendering effects of finite size, for the present set-up, similar to those of a chemical potential. Appropriately moving on the separation--temperature plane, it is possible to generate a peculiar behavior in the temperature dependence of the thermodynamic potential and of the condensate, compensating thermal with geometrical variations. A behavior similar to what we find here has been predicted to occur in bilayer graphene...
Energy-Casimir stability of hybrid Vlasov-MHD models
International Nuclear Information System (INIS)
Different variants of hybrid kinetic-fluid models are considered for describing the interaction of a bulk fluid plasma obeying magnetohydrodynamics (MHD) and an energetic component obeying a kinetic theory. Upon using the Vlasov kinetic theory for energetic particles, two planar Vlasov-MHD models are compared in terms of their stability properties. This is made possible by the Hamiltonian structures underlying the considered hybrid systems, whose infinite number of invariants makes the energy-Casimir method effective for determining stability. Equilibrium equations for the models are obtained from a variational principle and in particular a generalized hybrid Grad–Shafranov equation follows for one of the considered models. The stability conditions are then derived and discussed with particular emphasis on kinetic particle effects on classical MHD stability. (paper)
Casimir Effect in 2D Stringy Black Hole Backgrounds
Christodoulakis, T; Georgalas, B C; Vagenas, E C
2001-01-01
We consider the two-dimensional "Schwarzschild" and "Reissner-Nordstrom" stringy black holes as systems of Casimir type. We explicitly calculate the energy-momentum tensor of a massless scalar field satisfying Dirichlet boundary conditions on two one-dimensional "walls". These results are obtained using the Wald's axioms. Thermodynamical quantities such as pressure, specific heat, isothermal compressibility and entropy of the two-dimensional stringy black holes are calculated. A comparison is made between the obtained results and the laws of thermodynamics. The results obtained for the extremal (Q=M) stringy two-dimensional charged black hole are identical in all three different vacua used; a fact that indicates its quantum stability.
On the Casimir effect in a static chromomagnetic field
Bezerra, V B; Muniz, C R; Tahim, M O
2016-01-01
In this paper we compute the regularized vacuum energy associated with vectorial perturbations of the SU(2) massless Yang-Mills field. We regard Dirichlet and twisted boundary conditions in a chromomagnetic background, at zero temperature. Then, we analyse the behaviour of the Casimir energy in the weak and strong coupling regimens, and compare with similar results obtained for the scalar and spinorial fields in a magnetic field background. In the weak coupling scenario, we show that it is necessary to introduce mass in the perturbations in order to make manifest the effects due to the chromomagnetic field. Otherwise, in the strong coupling regimen, we evaluate the effects of the mass as well as of a compact extra dimension on the stabilization of the regularized vacuum energy.
Boström, Mathias; Baldissera, Gustavo; Persson, Clas; Ninham, Barry W
2012-01-01
We consider the interaction between a ZnO nanorod and a SiO2 nanorod in bromobenzene. Using optical data for the interacting objects and ambient we calculate the force - from short-range attractive van der Waals force to intermediate range repulsive Casimir-Lifshitz force to long range entropically driven attraction. The nonretarded van der Waals interaction is attractive at all separations. We demonstrate a retardation driven repulsion at intermediate separations. At short separations (in the nonretarded limit) and at large separations (in the classical limit) the interaction is attractive. These effects can be understood from an analysis of multiple crossings of the dielectric functions of the three media as functions of imaginary frequencies.
Faster-than-light Phenomenon of the Casimir Effect%论Casimir效应中的超光速现象
Institute of Scientific and Technical Information of China (English)
黄志洵
2012-01-01
The Casimir force was predicted in 1948 by Dutch physicist Hendrik Casimir,he realized that when calculating the energy between two parallel uncharged conducting plates, only those virtual photons whose wavelengths fit an integral number of times into the gap should be counted. Each mode contributes to a pressure on the plates,and the infinite number of modes outside the plates is greater than the infinite number inside the plates, resulting in a small force drawing the plates together. There are many methods to calculate the Casimir effect. For example,the Green function expression of the Casimir energy was applied,and the Casimir energy between the plates with four kinds of boundary condition was calculated by using that method. Then, we say that the change in the vacuum structure enforced by the plates. There are two kinds of vacuum, one is usual vacuum or free vacuum （ outside the plates）. Another is the negative energy vacuum （inside the plates）. They cause a change in the light speed for electromagnetic waves propagating perpendicular to the plates： △c/c≡ 1.6 × 10^ -6d^-4 ,and d is the plate distance. When d = 10^ -9m （ lnm）, ac = 10^-24c. Then,a two-loop QED effect,uncovered by K. Scharnhorst,cause the phase and group velocities of an electromagnetic wave to slightly exceed c. Though the difference are too small, that raise in- teresting matters of principle Casimir effect still surprising after 64 years.%荷兰物理学家HendrikCasimir于1948年提出存在一种Casimir力-当3计算两个互相平行的不带电导体板之间的能量时，当板距d小于真空中虚光子的波长，长波排除，板外的无限多模式大于板内的无限多模式，造成一个小的力量使两板靠近。计算Casimir效应有许多方法，例如可用Green函数描写Casimir能，就可以计算与边界条件对应的4种情况。 可以认为真空中放置双板后改变了真空的结构，故有两种真空：板外的常态真空或
Casimir-Foucault interaction: Free energy and entropy at low temperature
Intravaia, Francesco; Ellingsen, Simen Å.; Henkel, Carsten
2010-09-01
It was recently found that thermodynamic anomalies which arise in the Casimir effect between metals described by the Drude model can be attributed to the interaction of fluctuating Foucault (or eddy) currents [F. Intravaia and C. Henkel, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.103.130405 103, 130405 (2009).] We focus on the transverse electric (TE) polarization, where the anomalies occur, and show explicitly that the two leading terms of the low-temperature correction to the Casimir free energy of interaction between two plates are identical to those pertaining to the Foucault current interaction alone, up to a correction which is very small for good metals. Moreover, a mode density along real frequencies is introduced, showing that the TE contribution to the Casimir free energy, as given by the Lifshitz theory, separates in a natural manner into contributions from eddy currents and propagating cavity modes, respectively. The latter have long been known to be of little importance to the low-temperature Casimir anomalies. This convincingly demonstrates that eddy current modes are responsible for the large temperature correction to the Casimir effect between Drude metals, predicted by the Lifshitz theory, but not observed in experiments.
Casimir Energy for a Coupled Fermion-Kink System and its stability
Gousheh, Siamk Sadat; Shahkarami, Leila
2012-01-01
We compute the Casimir energy for a system consisting of a fermion and a pseudoscalar field in the form of a prescribed kink. This model is not exactly solvable and we use the phase shift method to compute the Casimir energy. We use the relaxation method to find the bound states and the Runge-Kutta-Fehlberg method to obtain the scattering wavefunctions of the fermion in the whole interval of $x$. The resulting phase shifts are consistent with the weak and strong forms of the Levinson theorem. Then, we compute and plot the Casimir energy as a function of the parameters of the pseudoscalar field, i.e. the slope of $\\phi(x)$ at x=0 ($\\mu$) and the value of $\\phi(x)$ at infinity ($\\theta_0$). In the graph of the Casimir energy as a function of $\\mu$ there is a sharp maximum occurring when the fermion bound state energy crosses the line of E=0. Furthermore, this graph shows that the Casimir energy goes to zero for $\\mu\\rightarrow 0$, and also for $\\mu\\rightarrow \\infty$ when $\\theta_0$ is an integer multiple of $\\...
Characteristic properties of the Casimir free energy for metal films deposited on metallic plates
Klimchitskaya, G. L.; Mostepanenko, V. M.
2016-04-01
The Casimir free energy and pressure of thin metal films deposited on metallic plates are considered using the Lifshitz theory and the Drude and plasma model approaches to the role of conduction electrons. The bound electrons are taken into account by using the complete optical data of film and plate metals. It is shown that for films of several tens of nanometers thickness the Casimir free energy and pressure calculated using these approaches differ by hundreds and thousands percent and can be easily discriminated experimentally. According to our results, the free energy of a metal film does not vanish in the limiting case of ideal metal if the Drude model approach is used in contradiction with the fact that the fluctuating field cannot penetrate in its interior. Numerical computations of the Casimir free energy and pressure of Ag and Au films deposited on Cu and Al plates have been performed using both theoretical approaches. It is shown that the free energy of a film can be both negative and positive depending on the metals used. For a Au film on a Ag plate and vice versa the Casimir energy of a film changes its sign with increasing film thickness. Applications of the obtained results for resolving the Casimir puzzle and the problem of stability of thin films are discussed.
Casimir-Foucault interaction: Free energy and entropy at low temperature
International Nuclear Information System (INIS)
It was recently found that thermodynamic anomalies which arise in the Casimir effect between metals described by the Drude model can be attributed to the interaction of fluctuating Foucault (or eddy) currents [F. Intravaia and C. Henkel, Phys. Rev. Lett. 103, 130405 (2009).] We focus on the transverse electric (TE) polarization, where the anomalies occur, and show explicitly that the two leading terms of the low-temperature correction to the Casimir free energy of interaction between two plates are identical to those pertaining to the Foucault current interaction alone, up to a correction which is very small for good metals. Moreover, a mode density along real frequencies is introduced, showing that the TE contribution to the Casimir free energy, as given by the Lifshitz theory, separates in a natural manner into contributions from eddy currents and propagating cavity modes, respectively. The latter have long been known to be of little importance to the low-temperature Casimir anomalies. This convincingly demonstrates that eddy current modes are responsible for the large temperature correction to the Casimir effect between Drude metals, predicted by the Lifshitz theory, but not observed in experiments.
A Toy Cosmology Using a Hubble-Scale Casimir Effect
Directory of Open Access Journals (Sweden)
Michael E. McCulloch
2014-02-01
Full Text Available The visible mass of the observable universe agrees with that needed for a flat cosmos, and the reason for this is not known. It is shown that this can be explained by modelling the Hubble volume as a black hole that emits Hawking radiation inwards, disallowing wavelengths that do not fit exactly into the Hubble diameter, since partial waves would allow an inference of what lies outside the horizon. This model of “horizon wave censorship” is equivalent to a Hubble-scale Casimir effect. This incomplete toy model is presented to stimulate discussion. It predicts a minimum mass and acceleration for the observable universe which are in agreement with the observed mass and acceleration, and predicts that the observable universe gains mass as it expands and was hotter in the past. It also predicts a suppression of variation on the largest cosmic scales that agrees with the low-l cosmic microwave background anomaly seen by the Planck satellite.
Dynamical Casimir effect and the black body spectrum
International Nuclear Information System (INIS)
Creation of scalar massless particles in two-dimensional Minkowski space time-as predicted by the dynamical Casimir effect-is studied for the case of a semitransparent mirror initially at rest, then accelerating for some finite time, along a specified trajectory, and finally moving with constant velocity. When the reflection and transmission coefficients are those in the model proposed by Barton, Calogeracos and Nicolaevici [r(w) = -iα/(ω + iα) and s(w) = ω/(ω + iα), with α ≥ 0], the Bogoliubov coefficients on the back side of the mirror can be computed exactly. This allows us to prove that, when α is very large (case of an ideal, perfectly reflecting mirror) a thermal emission of scalar massless particles obeying Bose-Einstein statistics is radiated from the mirror (a black body radiation), in accordance with previous results in the literature. However, when α is finite (semitransparent mirror, a physically realistic situation) the striking result is obtained that the thermal emission of scalar massless particles obeys Fermi-Dirac statistics. Possible consequences of this result are envisaged. (fast track communication)
Casimir effect on the lattice: U(1) gauge theory in two spatial dimensions
Chernodub, M N; Molochkov, A V
2016-01-01
We propose a general numerical method to study the Casimir effect in lattice gauge theories. We illustrate the method by calculating the energy density of zero-point fluctuations around two parallel wires of finite static permittivity in Abelian gauge theory in two spatial dimensions. We discuss various subtle issues related to the lattice formulation of the problem and show how they can successfully be resolved. Finally, we calculate the Casimir potential between the wires of a fixed permittivity, extrapolate our results to the limit of ideally conducting wires and demonstrate excellent agreement with a known theoretical result.
Casimir Effect at finite temperature for the CPT-even extension of QED
Silva, L M; Helayël-Neto, J A
2016-01-01
By the thermofield dynamics (TFD) formalism we obtain the energy-momentum tensor for the Electromagnetism with Lorentz Breaking Even term of the Standard Model Extended (SME) Sector in a topology $S^{1}\\times S^{1}\\times R^{2}$. We carry out the compactification by a generalized TFD-Bogoliubov transformation that is used to define a renormalized energy-momentum tensor, and the Casimir energy and pressure at finite temperature are then derived. A comparative analysis with the electromagnetic case is developed, and we remark the influence of the background in the traditional Casimir effect.
A novel experimental approach for the detection of the dynamical Casimir effect
Energy Technology Data Exchange (ETDEWEB)
Braggio, C. [Ferrara Univ. (Italy). Dipt. di Fisica; Bressi, G. [Istituto Nazionale di Fisica Nucleare, Pavia (Italy); Carugno, G.; Del Noce, C. [Istituto Nazionale di Fisica Nucleare, Padova (Italy); Galeazzi, G.; Lombardi, A.; Palmieri, A.; Ruoso, G. [Istituto Nazionale di Fisica Nucleare, LNL, Legnaro (Italy); Zanello, D. [Istituto Nazionale di Fisica Nucleare, Rome (Italy)
2005-06-01
In order to observe the Casimir radiation we propose a new experimental scheme with no mechanically moving mirror. In fact we estimate that the power required for a sustained mechanical vibration would be beyond present experimental possibilities. Our apparatus consists of a superconducting electromagnetic resonant cavity with a wall covered by a semiconductor layer whose reflectivity is driven by a laser at giga-hertz frequencies. The semiconductor thus acts as a moving mirror. Preliminary laboratory tests showed that a semiconductor can indeed reflect microwaves as efficiently as a conductor. In this paper we present the complete scheme that we intend to set up for the detection of the Casimir radiation. (authors)
Maasilta, I. J.; Puurtinen, T. A.; Tian, Y.; Geng, Z.
2016-07-01
We discuss two alternative and complementary means of controlling radial phonon conduction for bolometers in two dimensions: by using phononic crystals or by roughening the surface of the membranes (Casimir limit). For phononic crystals, we present new experiments with a modified geometry and a larger hole periodicity than before, achieving a low thermal conductance {˜ }2 pW/K at 150 mK. Calculations in the Casimir limit, on the other hand, show that for small detector dimensions thermal conductance below 1 fW/K seems achievable.
MIR status report: an experiment for the measurement of the dynamical Casimir effect
Energy Technology Data Exchange (ETDEWEB)
Agnesi, A; Pirzio, F; Reali, G [Dipartimento di Elettronica, Universita di Pavia, Via Ferrata 1, 27100 Pavia (Italy); Braggio, C; Carugno, G [INFN-Sezione di Padova, Via Marzolo 8, 35131 Padova (Italy); Bressi, G [INFN-Sezione di Pavia, Via U. Bassi 6, 27100 Pavia (Italy); Galeazzi, G; Ruoso, G [INFN-Laboratori Nazionali di Legnaro, Viale dell' Universita 2, 35020 Legnaro (Italy); Zanello, D [INFN-Sezione di Roma, P.le A. Moro 2, 00185 Roma (Italy)], E-mail: Giuseppe.Ruoso@lnl.infn.it
2008-04-25
In this paper, the status of the experiment MIR (motion induced radiation) is reported. This experiment aims at measuring for the first time the dynamical Casimir effect by using an effective motion of a wall of a superconducting microwave resonant cavity. Effective motion is produced by periodic illumination of a semiconductor slab by means of an ultra-high-frequency amplitude modulated laser.
Casimir effect of the Maxwell-Chern-Simons field for tow non-parallel lines boundary
International Nuclear Information System (INIS)
Based on the Faddeev formalism of path-integral quantization for a constrained Hamiltonian system, the Casimir effect between two non-parallel lines in the (2 +1)-dimensional space is calculated by using conformal mapping and Plana summation formula in the theory of complex variable function. Without introducing any cutoff of parameter, the finite analytical expression is obtained
Guérout, R.; Lambrecht, A.; Milton, K. A.; Reynaud, S.
2016-08-01
We reply to the "Comment on `Lifshitz-Matsubara sum formula for the Casimir pressure between magnetic metallic mirrors.' " We believe the comment misrepresents our papers, and fails to provide a plausible resolution to the conflict between theory and experiment.
Sensitive measurement of forces at the micron scale using Bloch oscillations of ultracold atoms.
Carusotto, I; Pitaevskii, L; Stringari, S; Modugno, G; Inguscio, M
2005-08-26
We show that Bloch oscillations of ultracold fermionic atoms in the periodic potential of an optical lattice can be used for a sensitive measurement of forces at the micrometer length scale, e.g., in the vicinity of a dielectric surface. In particular, the proposed approach allows us to perform a local and direct measurement of the Casimir-Polder force which is, for realistic experimental parameters, as large as 10(-4) gravity.
Effective forces between colloids at interfaces induced by capillary wave-like fluctuations
Lehle, H.; Oettel, M; Dietrich, S.
2006-01-01
We calculate the effective force mediated by thermally excited capillary waves between spherical or disklike colloids trapped at a fluid interface. This Casimir type interaction is shown to depend sensitively on the boundary conditions imposed at the three-phase contact line. For large distances between the colloids an unexpected cancellation of attractive and repulsive contributions is observed leading to a fluctuation force which decays algebraically very rapidly. For small separations the ...
An improved proximity force approximation for electrostatics
Fosco, C D; Mazzitelli, F D
2012-01-01
A quite straightforward approximation for the electrostatic interaction between two perfectly conducting surfaces suggests itself when the distance between them is much smaller than the characteristic lengths associated to their shapes. Indeed, in the so called "proximity force approximation" the electrostatic force is evaluated by first dividing each surface into a set of small flat patches, and then adding up the forces due two opposite pairs, the contribution of which are approximated as due to pairs of parallel planes. This approximation has been widely and successfully applied to different contexts, ranging from nuclear physics to Casimir effect calculations. We present here an improvement on this approximation, based on a derivative expansion for the electrostatic energy contained between the surfaces. The results obtained could be useful to discuss the geometric dependence of the electrostatic force, and also as a convenient benchmark for numerical analyses of the tip-sample electrostatic interaction i...
Campoamor-Stursberg, R
2008-01-01
Given a semidirect product $\\frak{g}=\\frak{s}\\uplus\\frak{r}$ of semisimple Lie algebras $\\frak{s}$ and solvable algebras $\\frak{r}$, we construct polynomial operators in the enveloping algebra $\\mathcal{U}(\\frak{g})$ of $\\frak{g}$ that commute with $\\frak{r}$ and transform like the generators of $\\frak{s}$, up to a functional factor that turns out to be a Casimir operator of $\\frak{r}$. Such operators are said to generate a virtual copy of $\\frak{s}$ in $\\mathcal{U}(\\frak{g})$, and allow to compute the Casimir operators of $\\frak{g}$ in closed form, using the classical formulae for the invariants of $\\frak{s}$. The behavior of virtual copies with respect to contractions of Lie algebras is analyzed. Applications to the class of Hamilton algebras and their inhomogeneous extensions are given.
Finite temperature Casimir effect for massive scalars in a magnetic field
Erdas, Andrea
2013-01-01
The finite temperature Casimir effect for a charged, massive scalar field confined between very large, perfectly conducting parallel plates is studied using the zeta function regularization technique. The scalar field satisfies Dirichlet boundary conditions at the plates and a magnetic field perpendicular to the plates is present. Four equivalent expressions for the zeta function are obtained, which are exact to all orders in the magnetic field strength, temperature, scalar field mass, and plate distance. The zeta function is used to calculate the Helmholtz free energy of the scalar field and the Casimir pressure on the plates, in the case of high temperature, small plate distance, strong magnetic field and large scalar mass. In all cases, simple analytic expressions of the zeta function, free energy and pressure are obtained, which are very accurate and valid for practically all values of temperature, plate distance, magnetic field and mass.
On the Difference Between the Vacuum Casimir Energies for Grounded and Isolated Conductors
Fosco, C D; Mazzitelli, F D
2016-01-01
We study the vacuum (i.e., zero-temperature) Casimir energy for a system of neutral conductors which are isolated, as opposed to grounded. The former is meant to describe a situation where the total charge on each conductor, as well as all of its fluctuations, vanishes, while the latter describes a situation where the conductors are connected to a charge reservoir. We compute the difference between the vacuum energies for a given system of conductors, but subjected to the two different conditions stated above. The results can be written in terms of a generalized, frequency-dependent capacitance matrix of the system. Using a multipolar expansion, we show that the grounded Casimir energy includes a monopole-monopole interaction term that is absent in the isolated case in the large distance limit
Klimchitskaya, G. L.; Mostepanenko, V. M.
2016-08-01
Recently Guérout et al. [Phys. Rev. E 93, 022108 (2016), 10.1103/PhysRevE.93.022108] advocated that the lossless plasma model has to be redefined as the limit of the Drude model when the relaxation parameter goes to zero. It was claimed that the previously used plasma model cannot correctly describe the Casimir pressure between two plates made of both nonmagnetic and magnetic metals and has to be replaced with the redefined one. We show that the suggested redefinition does not satisfy necessary physical requirements imposed on the dielectric permittivity. We also present a plausible explanation for the fact that the lossless plasma model describes the Casimir pressure correctly even though it does not match the optical and electrical properties of metals.
Casimir energy in a small volume multiply connected static hyperbolic pre-inflationary Universe
Müller, D; Opher, R; Muller, Daniel; Fagundes, Helio V.; Opher, Reuven
2001-01-01
A few years ago, Cornish, Spergel and Starkman (CSS), suggested that a multiply connected ``small'' Universe could allow for classical chaotic mixing as a pre-inflationary homogenization process. The smaller the volume, the more important the process. Also, a smaller Universe has a greater probability of being spontaneously created. Previously DeWitt, Hart and Isham (DHI) calculated the Casimir energy for static multiply connected flat space-times. Due to the interest in small volume hyperbolic Universes (e.g. CSS), we generalize the DHI calculation by making a a numerical investigation of the Casimir energy for a conformally coupled, massive scalar field in a static Universe, whose spatial sections are the Weeks manifold, the smallest Universe of negative curvature known. In spite of being a numerical calculation, our result is in fact exact. It is shown that there is spontaneous vacuum excitation of low multipolar components.
Casimir Dark Energy, Stabilization of the Extra Dimensions and Gauss-Bonnet Term
Wongjun, Pitayuth
2013-01-01
Casimir dark energy model in five-dimensional and six-dimensional spacetime including non-relativistic matter and Gauss-Bonnet term is investigated. The Casimir energy can play the role of dark energy to drive the late-time acceleration of the universe while the radius of the extra dimensions can be stabilized. The qualitative analysis in radion picture in four-dimensional spacetime shows that the contribution from Gauss-Bonnet term will effectively slows down the radion field at the beginning time. Therefore, the radion field does not pass minimum point of the effective potential before the minimum the potential exists. This leads to the stabilizing mechanism of the extra dimensions eventually.
Aharonov-Bohm phases and Dynamical Casimir Effect in a quantum LC circuit
Yao, Yuan
2016-01-01
We study novel types of contributions to the partition function of the Maxwell system defined on a small compact manifold ${\\mathbb{M}}$ with nontrivial mappings $\\pi_1[U(1)]\\cong\\mathbb{Z}$. These novel contributions cannot be described in terms of conventional physical propagating photons with two transverse polarizations, and instead emerge as a result of tunneling transitions between topologically different but physically identical vacuum winding states. These new terms give an extra contribution to the Casimir pressure, yet to be measured. We argue that if the same system is considered in the background of a small external time-dependent E\\&M field, then real physical photons will be emitted from the vacuum, similar to the dynamical Casimir effect (DCE) where photons are radiated from the vacuum due to time-dependent boundary conditions. We propose an experimental realization of such small effects using a microwave cavity. We also comment on the possible cosmological implications of this effect.
Guérout, R.; Lambrecht, A.; Milton, K. A.; Reynaud, S.
2014-10-01
We carefully reexamine the conditions of validity for the consistent derivation of the Lifshitz-Matsubara sum formula for the Casimir pressure between metallic plane mirrors. We recover the usual expression for the lossy Drude model but not for the lossless plasma model. We give an interpretation of this new result in terms of the modes associated with the Foucault currents, which play a role in the limit of vanishing losses, in contrast to common expectations.
Casimir Effect of Massive Scalar Field with Hybrid Boundary Condition in (1+1)-Dimensional Spacetime
Institute of Scientific and Technical Information of China (English)
HE Xiao-Kai; LIU Wen-Biao; QIU Wei-Gang
2009-01-01
The Casimir energy of maesive scalar field with hybrid (Dirichlet-Neumann) boundary condition is calcu-lated. In order to regularize the model, the typical methods named as mode summation method and Green's function method are used respectively. It is found that the regularized zero-point energy density depends on the scalar field's mass. When the field is massless, the result is consistent with previous literatures.
Casimir Effect at finite temperature for the CPT-even extension of QED
Silva, L. M.; Belich, H.; Helayël-Neto, J. A.
2016-01-01
By the thermofield dynamics (TFD) formalism we obtain the energy-momentum tensor for the Electromagnetism with Lorentz Breaking Even term of the Standard Model Extended (SME) Sector in a topology $S^{1}\\times S^{1}\\times R^{2}$. We carry out the compactification by a generalized TFD-Bogoliubov transformation that is used to define a renormalized energy-momentum tensor, and the Casimir energy and pressure at finite temperature are then derived. A comparative analysis with the electromagnetic c...
Bezerra, V. B.; Klimchitskaya, G. L.; Mostepanenko, V. M.; Romero, C.
2016-01-01
We propose an experiment for measuring the effective Casimir pressure between two parallel SiC plates with aligned nuclear spins. The prospective constraints on an axion-neutron coupling constant for both hadronic and GUT axions are calculated using the process of one-axion exchange. For this purpose, a general expression for the additional pressure arising between two polarized plates due to the exchange of one axion between their constituent fermions is derived. We demonstrate that only the...
The Casimir-Polder effect for a stack of conductive planes
Khusnutdinov, Nail; Kashapov, Rashid; Woods, Lilia M.
2016-01-01
The Casimir-Polder interaction between an atom and a multilayered system composed of infinitely thin planes is considered using the zeta-function regularization approach with summation of the zero-point energies. As a prototype material, each plane is represented by a graphene sheet whose optical response is described by a constant conductivity or Drude-Lorentz model conductivity. Asymptotic expressions for various separations are derived and compared to numerical calculations. We distinguish...
Magnetic field corrections to the repulsive Casimir effect at finite temperature
Erdas, Andrea
2015-01-01
I investigate the finite temperature Casimir effect for a charged and massless scalar field satisfying mixed (Dirichlet-Neumann) boundary conditions on a pair of plane parallel plates of infinite size. The effect of a uniform magnetic field, perpendicular to the plates, on the Helmholtz free energy and Casimir pressure is studied. The zeta-function regularization technique is used to obtain finite results. Simple analytic expressions are obtained for the zeta function and the free energy, in the limits of small plate distance, high temperature and strong magnetic field. The Casimir pressure is obtained in each of the three limits and the situation of a magnetic field present between and outside the plates, as well as that of a magnetic field present only between the plates is examined. It is discovered that, in the small plate distance and high temperature limits, the repulsive pressure is less when the magnetic field is present between the plates but not outside, than it is when the magnetic field is present...
All-optical dynamical Casimir effect in a three-dimensional terahertz photonic band gap
Hagenmüller, David
2016-06-01
We identify an architecture for the observation of all-optical dynamical Casimir effect in realistic experimental conditions. We suggest that by integrating quantum wells in a three-dimensional (3D) photonic band-gap material made out of large-scale (˜200 -μ m ) germanium logs, it is possible to achieve ultrastrong light-matter coupling at terahertz frequencies for the cyclotron transition of a two-dimensional electron gas interacting with long-lived optical modes, in which vacuum Rabi splitting is comparable to the Landau level spacing. When a short, intense electromagnetic transient of duration ˜250 fs and carrying a peak magnetic field ˜5 T is applied to the structure, the cyclotron transition can be suddenly tuned on resonance with a desired photon mode, switching on the light-matter interaction and leading to a Casimir radiation emitted parallel to the quantum well plane. The radiation spectrum consists of sharp peaks with frequencies coinciding with engineered optical modes within the 3D photonic band gap, and its characteristics are extremely robust to the nonradiative damping which can be large in our system. Furthermore, the absence of continuum with associated low-energy excitations for both electromagnetic and electronic quantum states can prevent the rapid absorption of the photon flux which is likely to occur in other proposals for all-optical dynamical Casimir effect.
Cysne, T; Oliver, D; Pinheiro, F A; Rosa, F S S; Farina, C
2014-01-01
We investigate the dispersive Casimir-Polder interaction between a Rubidium atom and a suspended graphene sheet subjected to an external magnetic field B. We demonstrate that this concrete physical system allows for an unprecedented control of dispersive interactions at micro and nanoscales. Indeed, we show that the application of an external magnetic field can induce a 80% reduction of the Casimir-Polder energy relative to its value without the field. We also show that sharp discontinuities emerge in the Casimir-Polder interaction energy for certain values of the applied magnetic field at low temperatures. Moreover, for sufficiently large distances these discontinuities show up as a plateau-like pattern with a quantized Casimir-Polder interaction energy, in a phenomenon that can be explained in terms of the quantum Hall effect. In addition, we point out the importance of thermal effects in the Casimir-Polder interaction, which we show that must be taken into account even for considerably short distances. In ...
Attonewton force detection using microspheres in a dual-beam optical trap in high vacuum
Ranjit, Gambhir; Stutz, Jordan H; Cunningham, Mark; Geraci, Andrew A
2015-01-01
We describe the implementation of laser-cooled silica microspheres as force sensors in a dual-beam optical dipole trap in high vacuum. Using this system we have demonstrated trap lifetimes exceeding several days, attonewton force detection capability, and wide tunability in trapping and cooling parameters. Measurements have been performed with charged and neutral beads to calibrate the sensitivity of the detector. This work establishes the suitability of dual beam optical dipole traps for precision force measurement in high vacuum with long averaging times, and enables future applications including the study of gravitational inverse square law violations at short range, Casimir forces, acceleration sensing, and quantum opto-mechanics.
Geometry-Induced Casimir Suspension of Oblate Bodies in Fluids
Rodriguez, Alejandro W.; Reid, M. T. Homer; Intravaia, Francesco; Woolf, Alexander; Dalvit, Diego A. R.; Capasso, Federico; Johnson, Steven G.
2013-11-01
We predict that a low-permittivity oblate body (disk-shaped object) above a thin metal substrate (plate with a hole) immersed in a fluid of intermediate permittivity will experience a metastable equilibrium (restoring force) near the center of the hole. Stability is the result of a geometry-induced transition in the sign of the force, from repulsive to attractive, that occurs as the disk approaches the hole—in planar or nearly planar geometries, the same material combination yields a repulsive force at all separations, in accordance with the Dzyaloshinskiĭ-Lifshitz-Pitaevskiĭ condition of fluid-induced repulsion between planar bodies. We explore the stability of the system with respect to rotations and lateral translations of the disks and demonstrate interesting transitions (bifurcations) in the rotational stability of the disks as a function of their size. Finally, we consider the reciprocal situation in which the disk-plate materials are interchanged and find that in this case the system also exhibits metastability. The forces in the system are sufficiently large to be observed in experiments and should enable measurements based on the diffusion dynamics of the suspended bodies.
Is the electrostatic force between a point charge and a neutral metallic object always attractive?
Levin, Michael
2010-01-01
We give an example of a geometry in which the electrostatic force between a point charge and a neutral metallic object is repulsive. The example consists of a point charge centered above a thin metallic hemisphere, positioned concave up. We show that this geometry has a repulsive regime using both a simple analytical argument and an exact calculation for an analogous two-dimensional geometry. Analogues of this geometry-induced repulsion can appear in many other contexts, including Casimir systems.
Phillips, Nicholas G.; Hu, B. L.
2000-10-01
We present calculations of the variance of fluctuations and of the mean of the energy momentum tensor of a massless scalar field for the Minkowski and Casimir vacua as a function of an intrinsic scale defined by a smeared field or by point separation. We point out that, contrary to prior claims, the ratio of variance to mean-squared being of the order unity is not necessarily a good criterion for measuring the invalidity of semiclassical gravity. For the Casimir topology we obtain expressions for the variance to mean-squared ratio as a function of the intrinsic scale (defined by a smeared field) compared to the extrinsic scale (defined by the separation of the plates, or the periodicity of space). Our results make it possible to identify the spatial extent where negative energy density prevails which could be useful for studying quantum field effects in worm holes and baby universes, and for examining the design feasibility of real-life ``time machines.'' For the Minkowski vacuum we find that the ratio of the variance to the mean-squared, calculated from the coincidence limit, is identical to the value of the Casimir case at the same limit for spatial point separation while identical to the value of a hot flat space result with a temporal point separation. We analyze the origin of divergences in the fluctuations of the energy density and discuss choices in formulating a procedure for their removal, thus raising new questions about the uniqueness and even the very meaning of regularization of the energy momentum tensor for quantum fields in curved or even flat spacetimes when spacetime is viewed as having an extended structure.
Lifshitz-Matsubara sum formula for the Casimir pressure between magnetic metallic mirrors
Guérout, R.; Lambrecht, A.; Milton, K. A.; Reynaud, S.
2016-02-01
We examine the conditions of validity for the Lifshitz-Matsubara sum formula for the Casimir pressure between magnetic metallic plane mirrors. As in the previously studied case of nonmagnetic materials [Guérout et al., Phys. Rev. E 90, 042125 (2014), 10.1103/PhysRevE.90.042125], we recover the usual expression for the lossy model of optical response, but not for the lossless plasma model. We also show that the modes associated with the Foucault currents play a crucial role in the limit of vanishing losses, in contrast to expectations.
Particle creation by a black hole as a consequence of the Casimir effect
Energy Technology Data Exchange (ETDEWEB)
Nugayev, R.M.
1987-08-01
Particle creation by a blackhole is investigated in terms of temperature corrections to the Casimir effect. The reduction of the Hawking effect to more familiar effects observed in the laboratory enables us to reveal the mechanism of particle creation. The blackbody nature of the Hawking radiation is due to the interaction of virtual particles with the surface of a ''cavity'' formed by the Schwarzschild gravitational field potential barrier. These particles are ''squeezed out'' by the contraction of the potential barrier and appear to an observer at J/sup +/ as the real blackbody ones.
Stress Tensors and Casimir Energies in the AdS/CFT Correspondence
Myers, R C
1999-01-01
We discuss various approaches to extracting the full stress-energy tensor of the conformal field theory from the corresponding supergravity solutions, within the framework of the Maldacena conjecture. This provides a more refined probe of the AdS/CFT correspondence. We apply these techniques in considering the Casimir energy of the conformal field theory on a torus. It seems that either generically the corresponding supergravity solutions are singular (i.e., involve regions of large string-scale curvatures), or that they are largely insensitive to the boundary conditions of the CFT on the torus.
Phonon-polaritons in Bose-Einstein condensates induced by Casimir-Polder interaction with graphene
Terças, H; Ribeiro, S.; Mendonça, J. T.
2014-01-01
We consider the mechanical coupling between a two-dimensional Bose-Einstein condensate with a graphene sheet via the vacuum fluctuations of the electromagnetic field which are at the origin of the so-called Casimir-Polder potential. By deriving a self-consistent set of equations governing the dynamics of the condensate and the flexural (out-of-plane) modes of the graphene, we can show the formation of a new type of purely acoustic quasi-particle excitation, a phonon-polariton resulting from t...
Self-adjointness and the Casimir effect with confined quantized spinor matter
Sitenko, Yurii A
2015-01-01
A generalization of the MIT bag boundary condition for spinor matter is proposed basing on the requirement that the Dirac hamiltonian operator be self-adjoint. An influence of a background magnetic field on the vacuum of charged spinor matter confined between two parallel material plates is studied. Employing the most general set of boundary conditions at the plates in the case of the uniform magnetic field directed orthogonally to the plates, we find the pressure from the vacuum onto the plates. In physically plausible situations, the Casimir effect is shown to be repulsive, independently of a choice of boundary conditions and of a distance between the plates.
MIR: An experiment for the measurement of the dynamical Casimir effect
Energy Technology Data Exchange (ETDEWEB)
Agnesi, A; Pirzio, F; Reali, G; Scarpa, D [Dipartimento di Elettronica, Universita di Pavia, Via Ferrata 1, 27100 Pavia (Italy); Braggio, C; Galeazzi, G [Dipartimento di Fisica, Universita di Padova, via Marzolo 8, 35131 Padova (Italy); Bressi, G [INFN sez. di Pavia, via Bassi 6, 27100 Pavia (Italy); Carugno, G [INFN sez. di Padova, via Marzolo 8, 35131 Padova (Italy); Valle, F Della; Messineo, G [INFN sez. di Trieste and Dipartimento di Fisica, Universita di Trieste, Via Valerio 2, 34127 Trieste (Italy); Ruoso, G [INFN lab. naz. Legnaro, viale dell' Universita 2, 35020 Legnaro (Pd) (Italy); Zanello, D, E-mail: Caterina.Braggio@pd.infn.i [INFN sez. di Roma, P.le A. Moro 2, 00185 Roma (Italy)
2009-04-01
In this paper we report the status of the experiment MIR (Motion Induced Radiation), aimed at the experimental verification of the dynamical Casimir effect. The stringent theoretical requirements to observe the effect are satisfied in a scheme in which the conductivity of a semiconductor inside a superconducting microwave resonant cavity is varied in time. Free carriers in the semiconductor are periodically excited and recombine at 5 GHz. In this process vacuum and thermal photons are parametrically amplified in a time interval of 200-500 ns.
Zeta Function Regularization in Casimir Effect Calculations and J. S. Dowker's Contribution
Elizalde, Emilio
2012-07-01
A summary of relevant contributions, ordered in time, to the subject of operator zeta functions and their application to physical issues is provided. The description ends with the seminal contributions of Stephen Hawking and Stuart Dowker and collaborators, considered by many authors as the actual starting point of the introduction of zeta function regularization methods in theoretical physics, in particular, for quantum vacuum fluctuation and Casimir effect calculations. After recalling a number of the strengths of this powerful and elegant method, some of its limitations are discussed. Finally, recent results of the so called operator regularization procedure are presented.
Quasi-polaritons in Bose-Einstein condensates induced by Casimir-Polder interaction with graphene.
Terças, H; Ribeiro, S; Mendonça, J T
2015-06-01
We consider the mechanical coupling between a two-dimensional Bose-Einstein condensate and a graphene sheet via the vacuum fluctuations of the electromagnetic field which are at the origin of the so-called Casimir-Polder potential. By deriving a self-consistent set of equations governing the dynamics of the condensate and the flexural (out-of-plane) modes of the graphene, we can show the formation of a new type of purely acoustic quasi-particle excitation, a quasi-polariton resulting from the coherent superposition of quanta of flexural and Bogoliubov modes. PMID:25966318
Casimir Effect at finite temperature for the Kalb-Ramond field
Belich, H; Helayël-Neto, J A; Santana, A E
2010-01-01
We use the thermofield dynamics (TFD) formalism to obtain the energy-momentum tensor for the Kalb-Ramond (KR) field in a topology $% S^{1}\\times S^{1}\\times R^{2}$. The compactification is carried out by a generalized TFD-Bogoliubov transformation that is used to define a renormalized energy-momentum tensor. The expressions for the Casimir energy and pressure at finite temperature are then derived. A comparative analysis with the electromagnetic case is developed, and the results may be important for applications, as in cuprate superconductivity, for instance.
Casimir Effect at finite temperature for the Kalb-Ramond field
Belich, H.; Silva, L. M.; Helayël-Neto, J. A.; Santana, A. E.
2010-01-01
We use the thermofield dynamics (TFD) formalism to obtain the energy-momentum tensor for the Kalb-Ramond (KR) field in a topology $% S^{1}\\times S^{1}\\times R^{2}$. The compactification is carried out by a generalized TFD-Bogoliubov transformation that is used to define a renormalized energy-momentum tensor. The expressions for the Casimir energy and pressure at finite temperature are then derived. A comparative analysis with the electromagnetic case is developed, and the results may be impor...
Tuning Casimir-Polder interactions in atom-metamaterial hybrid devices
Chan, Eng Aik; Adamo, Giorgio; Laliotis, Athanasios; Ducloy, Martial; Wilkowski, David
2016-01-01
We report on the coupling of a surface plasmonic mode with a thermal vapor of cesium atoms. The plasmonic resonance is created using a nano-structured metallic surface. By changing the geometrical properties of the metamaterial, we tune the plasmonic resonance wavelength with respect to the D2 line of cesium. When the two resonances are close, we observe a strong modification of the Casimir-Polder interaction accompanied by a change of the atomic lifetime. A proper tuning leads to an almost suppression of the frequency shift of the cesium transition. This result paves the way for precision atomic spectroscopy in the vicinity of a material surface.
The thermal Casimir-Polder interaction of an atom with spherical plasma shell
Khusnutdinov, Nail R.
2012-01-01
The van der Waals and Casimir-Polder interaction energy of an atom with an infinitely thin sphere with finite conductivity is investigated in the framework of the hydrodynamic approach at finite temperature. This configuration models the real interaction of an atom with fullerene. The Lifshitz approach is used to find the free energy. We find the explicit expression for the free energy and perform the analysis of it for i) high and low temperatures, ii) large radii of sphere and ii) short sep...
Interference phenomena in the dynamical Casimir effect for a single mirror with Robin conditions
Silva, Jeferson D. Lima; Braga, Alessandra N.; Rego, Andreson L. C.; Alves, Danilo T.
2015-07-01
In the literature, the interference phenomenon in the particle creation via the dynamical Casimir effect is investigated for cavities with two moving mirrors. Here, considering the Robin boundary condition (BC), we investigate the interference phenomenon produced by just a single moving mirror. Specifically, we consider a real massless scalar field in 1 +1 dimensions submitted to a Robin BC with a time-dependent Robin parameter at the instantaneous position of a moving mirror, and compute the expressions for the spectral distribution and the rate of created particles. These expressions, which include interference terms, generalize those found in the literature related to the isolated effects of a Robin BC with a time-dependent Robin parameter for a fixed mirror, or a Robin BC with a time-independent Robin parameter for a moving mirror. Differently from models where the problem of interference in the dynamical Casimir effect is considered for cavities with two Dirichlet moving mirrors, in the present model the spectrum is a continuum, and the interference pattern exhibits new features, in the sense that different regions of the spectrum can be affected in different manners by constructive or destructive effects. Furthermore, we also investigate interference in the context of superconducting circuits.
Impact of Casimir-Polder interaction on Poisson-spot diffraction at a dielectric sphere
Hemmerich, Joshua Leo; Reisinger, Thomas; Nimmrichter, Stefan; Fiedler, Johannes; Hahn, Horst; Gleiter, Herbert; Buhmann, Stefan Yoshi
2016-01-01
Diffraction of matter-waves is an important demonstration of the fact that objects in nature possess a mixture of particle-like and wave-like properties. Unlike in the case of light diffraction, matter-waves are subject to a vacuum-mediated interaction with diffraction obstacles. Here we present a detailed account of this effect through the calculation of the attractive Casimir-Polder potential between a dielectric sphere and an atomic beam. Furthermore, we use our calculated potential to make predictions about the diffraction patterns to be observed in an ongoing experiment where a beam of indium atoms is diffracted around a silicon dioxide sphere. The result is an amplification of the on-axis bright feature which is the matter-wave analogue of the well-known `Poisson spot' from optics. Our treatment confirms that the diffraction patterns resulting from our complete account of the sphere Casimir-Polder potential are indistinguishable from those found via a large-sphere non-retarded approximation in the discu...
Coupled-oscillator theory of dispersion and Casimir-Polder interactions.
Berman, P R; Ford, G W; Milonni, P W
2014-10-28
We address the question of the applicability of the argument theorem (of complex variable theory) to the calculation of two distinct energies: (i) the first-order dispersion interaction energy of two separated oscillators, when one of the oscillators is excited initially and (ii) the Casimir-Polder interaction of a ground-state quantum oscillator near a perfectly conducting plane. We show that the argument theorem can be used to obtain the generally accepted equation for the first-order dispersion interaction energy, which is oscillatory and varies as the inverse power of the separation r of the oscillators for separations much greater than an optical wavelength. However, for such separations, the interaction energy cannot be transformed into an integral over the positive imaginary axis. If the argument theorem is used incorrectly to relate the interaction energy to an integral over the positive imaginary axis, the interaction energy is non-oscillatory and varies as r(-4), a result found by several authors. Rather remarkably, this incorrect expression for the dispersion energy actually corresponds to the nonperturbative Casimir-Polder energy for a ground-state quantum oscillator near a perfectly conducting wall, as we show using the so-called "remarkable formula" for the free energy of an oscillator coupled to a heat bath [G. W. Ford, J. T. Lewis, and R. F. O'Connell, Phys. Rev. Lett. 55, 2273 (1985)]. A derivation of that formula from basic results of statistical mechanics and the independent oscillator model of a heat bath is presented.
Dynamical Casimir Effect in a small compact manifold for the Maxwell vacuum
Zhitnitsky, Ariel R
2015-01-01
We study novel type of contributions to the partition function of the Maxwell system defined on a small compact manifold ${\\mathbb{M}}$ such as torus. These new terms can not be described in terms of the physical propagating photons with two transverse polarizations. Rather, these novel contributions emerge as a result of tunnelling events when transitions occur between topologically different but physically identical vacuum winding states. These new terms give an extra contribution to the Casimir pressure, yet to be measured. We argue that if the same system is considered in the background of a small external time-dependent magnetic field, than there will be emission of photons from the vacuum, similar to the Dynamical Casimir Effect (DCE) when real particles are radiated from the vacuum due to the time-dependent boundary conditions. The difference with conventional DCE is that the dynamics of the vacuum in our system is not related to the fluctuations of the conventional degrees of freedom, the virtual phot...
Phillips, N G; Phillips, Nicholas. G.
2000-01-01
We present calculations of the variance of fluctuations and of the mean of the energy momentum tensor of a massless scalar field for the Minkowski and Casimir vacua as a function of an intrinsic scale defined by a smeared field or by point separation. We point out that contrary to prior claims, the ratio of variance to mean-squared being of the order unity is not necessarily a good criterion for measuring the invalidity of semiclassical gravity. For the Casimir topology we obtain expressions for the variance to mean-squared ratio as a function of the intrinsic scale (defined by a smeared field) compared to the extrinsic scale (defined by the separation of the plates, or the periodicity of space). Our results make it possible to identify the spatial extent where negative energy density prevails which could be useful for studying quantum field effects in worm holes and baby universe, and for examining the design feasibility of real-life `time-machines'. For the Minkowski vacuum we find that the ratio of the var...
Développement multipolaire de l'eﬀet Casimir dans la géométrie sphère-plan.
Canaguier-Durand, Antoine
2011-01-01
We evaluate the Casimir interaction between a sphere and a plane, at arbitrary temperature, accounting for imperfect reflection. This enables us to study the rich dependance of the Casimir effect on the geometry, and to estimate the error made by the proximity approximation (PFA) commonly used in this sphere-plane configuration, which is the one of the experiments. For this evaluation we apply the scattering method, based on the theory of optical networks, to the sphere-plane geometry. The te...
Energy Technology Data Exchange (ETDEWEB)
Niekerken, Ole
2009-06-15
In this diploma thesis the Casimir-Polder force at zero temperature and at finite temperatures is calculated by using a well-defined quantum field theory (formulated in position space) and the method of image charges. For the calculations at finite temperature KMS-states are used. The so defined temperature describes the temperature of the electromagnetic background. A one oscillator model for inhomogeneous dispersive absorbing dielectric material is introduced and canonically quantized to calculate the Casimir-Polder force at a dielectric interface at finite temperature. The model fulfils causal commutation relations and the dielectric function of the model fulfils the Kramer-Kronig relations. We then use the same methods to calculate the van der Waals force between two neutral atoms at zero temperature and at finite temperatures. It is shown that the high temperature behaviour of the Casimir-Polder force and the van der Waals force are independent of {Dirac_h}. This means that they have to be understood classically, what is then shown in an algebraic statistical theory by using classical KMS states. (orig.)
New experimental limits on non-Newtonian forces in the micrometer-range
Sushkov, A O; Dalvit, D A R; Lamoreaux, S K
2011-01-01
We report measurements of the short-range forces between two macroscopic gold-coated plates using a torsion pendulum. The force is measured for separations between 0.7 $\\mu$m and 7 $\\mu$m, and is well described by a combination of the Casimir force, including the finite-temperature correction, and an electrostatic force due to patch potentials on the plate surfaces. We use our data to place constraints on the Yukawa-type "new" forces predicted by theories with extra dimensions. We establish a new best bound for force ranges 0.4 $\\mu$m to 4 $\\mu$m, and, for forces mediated by gauge bosons propagating in $(4+n)$ dimensions and coupling to the baryon number, extract a $(4+n)$-dimensional Planck scale lower limit of $M_*>70$ TeV.
Bezerra, V B; Mostepanenko, V M; Romero, C
2016-01-01
We propose an experiment for measuring the effective Casimir pressure between two parallel SiC plates with aligned nuclear spins. The prospective constraints on an axion-neutron coupling constant for both hadronic and GUT axions are calculated using the process of one-axion exchange. For this purpose, a general expression for the additional pressure arising between two polarized plates due to the exchange of one axion between their constituent fermions is derived. We demonstrate that only the polarization component perpendicular to the plates contribute to the pressure. The obtained pressure can be both repulsive and attractive depending on whether the polarizations of both plates are unidirectional or directed in opposite directions. It is shown that although the constraints on an axion-electron coupling obtained in the case of magnetized plates are not competitive, the constraints on an axion-neutron coupling found for plates with polarized nuclear spins are of the same order of magnitude of those obtained ...
Finite temperature Casimir effect for charged massless scalars in a magnetic field
Erdas, Andrea
2013-01-01
The zeta function regularization technique is used to study the finite temperature Casimir effect for a charged and massless scalar field confined between parallel plates and satisfying Dirichlet boundary conditions at the plates. A magnetic field perpendicular to the plates is included. Three equivalent expressions for the zeta function are obtained, which are exact to all orders in the magnetic field strength, temperature and plate distance. These expressions of the zeta function are used to calculate the Helmholtz free energy of the scalar field and the pressure on the plates, in the case of high temperature, small plate distance and strong magnetic field. In all cases, simple analytic expressions are obtained for the free energy and pressure which are accurate and valid for practically all values of temperature, plate distance and magnetic field.
International Nuclear Information System (INIS)
We investigate the effects of dynamical Casimir effect in superradiant light scattering by Bose—Einstein condensate in an optomechanical cavity. The system is studied using both classical and quantized mirror motions. The cavity frequency is harmonically modulated in time for both the cases. The main quantity of interest is the number of intracavity scattered photons. The system has been investigated under the weak and strong modulations. It has been observed that the amplitude of the scattered photons is more for the classical mirror motion than the quantized mirror motion. Also, initially, the amplitude of scattered photons is high for lower modulation amplitude than higher modulation amplitude. We also found that the behavior of the plots are similar under strong and weak modulations for the quantized mirror motion. (general)
Efficient near-field energy transfer and relieved Casimir stiction between sub-wavelength gratings
Liu, Xianglei; Zhao, Bo; Zhang, Zhuomin
2015-03-01
The promising applications of near-field heat transfer in thermophotovoltaic devices, thermal imaging, thermal rectifiers, and local thermal management have motivated the search for nanostructures capable of supporting higher efficiency or greater heat flux than simple planar substances. In this work, efficient and delocalized radiative heat transfer between two aligned 1D sub-wavelength gratings is demonstrated based on the scattering theory using the rigorous coupled-wave analysis (RCWA). It is shown that the heat flux can be greatly enhanced and the accurate prediction may differ significantly from that of the geometry-based Derjaguin's proximity approximation (PA). The underlying mechanism is attributed to the excitation of hyperbolic modes that increase the energy transmission by supporting propagation of waves with large parallel wavevectors and. Besides efficient energy transport, the performance is robust, insensitive to the relative lateral shift. In addition, the Casimir stiction considering both quantum and thermal fluctuations is found to be relieved compared with bulks.
The thermal Casimir-Polder interaction of an atom with spherical plasma shell
Khusnutdinov, Nail R
2012-01-01
The van der Waals and Casimir-Polder interaction energy of an atom with an infinitely thin sphere with finite conductivity is investigated in the framework of the hydrodynamic approach at finite temperature. The Lifshits approach is used to find the free energy. We find the close expression for the free energy and make the analysis of it for i) high and low temperatures, ii) large radii of sphere and ii) short distance from sphere. At low temperatures the thermal part of the free energy tends to zero as forth power of the temperature while for high temperatures it is proportional to the first degree of the temperature. We show that the entropy of this system is positive for small radii of sphere and it becomes negative at low temperatures and for large radii of the sphere.
Casimir-Polder potential in a dielectric medium out of thermal equilibrium
International Nuclear Information System (INIS)
The Casimir-Polder potential between a pair of atoms or molecules, either one of which may be excited, in a dielectric medium out of thermal equilibrium is obtained using a field operator that accounts for the attenuation or amplification of the radiation. Two contributions to the intermolecular potential are identified. One term is that induced by the excitations and relaxations that the interacting molecules experience due to the thermal bath, obtained using the resonance energy transfer rate and the Wigner-Weisskopf model. The second contribution arises as a consequence of the polarization induced in the interacting molecules by vacuum and thermal radiation. A number of disagreements between the present theory and several previously reported formulations examining this intermolecular potential are revealed.
On the Derivative Expansion for the Electromagnetic Casimir Free Energy at High Temperatures
Fosco, C D; Mazzitelli, F D
2015-01-01
We study the contribution of the thermal zero modes to the Casimir free energy, in the case of a fluctuating electromagnetic (EM) field in the presence of real materials described by frequency-dependent, local and isotropic permittivity ($\\epsilon$) and permeability ($\\mu$) functions. Those zero modes, present at any finite temperature, become dominant at high temperatures, since the theory is dimensionally reduced. Our work, within the context of the Derivative Expansion (DE) approach, focusses on the emergence of non analyticities in that dimensionally reduced theory. We conclude that the DE is well defined whenever the function $\\Omega(\\omega)$, defined by $[\\Omega(\\omega)]^2 \\equiv \\omega^2\\epsilon(\\omega)$, vanishes in the zero-frequency limit, for at least one of the two material media involved.
Casimir effect of two conducting parallel plates in a general weak gravitational field
Energy Technology Data Exchange (ETDEWEB)
Nazari, Borzoo [University of Tehran, Faculty of Engineering Science, College of Engineering, P.O. Box 11155-4563, Tehran (Iran, Islamic Republic of)
2015-10-15
We calculate the finite vacuum energy density of the scalar and electromagnetic fields inside a Casimir apparatus made up of two conducting parallel plates in a general weak gravitational field. The metric of the weak gravitational field has a small deviation from flat spacetime inside the apparatus, and we find it by expanding the metric in terms of small parameters of the weak background. We show that the metric found can be transformed via a gauge transformation to the Fermi metric. We solve the Klein-Gordon equation exactly and find mode frequencies in Fermi spacetime. Using the fact that the electromagnetic field can be represented by two scalar fields in the Fermi spacetime, we find general formulas for the energy density and mode frequencies of the electromagnetic field. Some well-known weak backgrounds are examined and consistency of the results with the literature is shown. (orig.)
Does the Transverse Electric Zero Mode Contribute to the Casimir Effect for a Metal?
Høye, J S; Aarseth, J B; Milton, K A
2003-01-01
The finite temperature Casimir free energy, entropy, and internal energy are considered anew for a conventional parallel-plate configuration, in the light of current discussions in the literature. In the case of an "ideal" metal, characterized by a refractive index equal to infinity for all frequencies, we recover, via a somewhat unconventional method, conventional results for the temperature dependence, meaning that the zero-frequency transverse electric mode contributes the same as the transverse magnetic mode. For a real metal, however, approximately obeying the Drude dispersive model at low frequencies, we find that the zero-frequency transverse electric mode does not contribute at all. This would appear to lead to an observable temperature dependence and a violation of the third law of thermodynamics. It had been suggested that the source of the difficulty was the behaviour of the reflection coefficient for perpendicular polarization but we show that this is not the case. By introducing a simplified mode...
Institute of Scientific and Technical Information of China (English)
李铜忠
2004-01-01
A new concise method is presented for the calculation of the ground-state energy of the electromagnetic field and matter field interacting system. With the assumption of squeezed-like state, a new vacuum state is obtained for the interacting system. The energy of the new vacuum state is lower than that given by the second-order perturbation theory in existing theories. In our theory, the Casimir effect is attributed neither to the quantum fluctuation in the zero-point energy of the genuine electromagnetic field nor to that in the zero-point energy of the genuine matter field, but to that in the vacuum state of the interacting system. Both electromagnetic field and matter field are responsible for the Casimir effect.
Energy Technology Data Exchange (ETDEWEB)
Lim, S C [Faculty of Engineering, Multimedia University, Jalan Multimedia, Cyberjaya, 63100, Selangor Darul Ehsan (Malaysia); Teo, L P [Faculty of Information Technology, Multimedia University, Jalan Multimedia, Cyberjaya, 63100, Selangor Darul Ehsan (Malaysia)
2007-09-21
We derive rigorously explicit formulae of the Casimir free energy at finite temperature for massless scalar field and electromagnetic field confined in a closed rectangular cavity with different boundary conditions by a zeta regularization method. We study both the low and high temperature expansions of the free energy. In each case, we write the free energy as a sum of a polynomial in temperature plus exponentially decay terms. We show that the free energy is always a decreasing function of temperature. In the cases of massless scalar field with the Dirichlet boundary condition and electromagnetic field, the zero temperature Casimir free energy might be positive. In each of these cases, there is a unique transition temperature (as a function of the side lengths of the cavity) where the Casimir energy changes from positive to negative. When the space dimension is equal to two and three, we show graphically the dependence of this transition temperature on the side lengths of the cavity. Finally we also show that we can obtain the results for a non-closed rectangular cavity by letting the size of some directions of a closed cavity go to infinity, and we find that these results agree with the usual integration prescription adopted by other authors.
Milton, Kimball A; Parashar, Prachi; Kalauni, Pushpa; Murphy, Taylor
2016-01-01
Motivated by a desire to understand quantum fluctuation energy densities and stress within a spatially varying dielectric medium, we examine the vacuum expectation value for the stress tensor of a scalar field with arbitrary conformal parameter, in the background of a given potential that depends on only one spatial coordinate. We regulate the expressions by incorporating a temporal-spatial cutoff in the (imaginary) time and transverse-spatial directions. The divergences are captured by the zeroth- and second-order WKB approximations. Then the stress tensor is "renormalized" by omitting the terms that depend on the cutoff. The ambiguities that inevitably arise in this procedure are both duly noted and restricted by imposing certain physical conditions; one result is that the renormalized stress tensor exhibits the expected trace anomaly. The renormalized stress tensor exhibits no pressure anomaly, in that the principle of virtual work is satisfied for motions in a transverse direction. We then consider a pote...
Short-range force detection using optically-cooled levitated microspheres
Geraci, Andrew A; Kitching, John
2010-01-01
We propose an experiment using optically trapped and cooled dielectric microspheres for the detection of short-range forces. The center-of-mass motion of a microsphere trapped in vacuum can experience extremely low dissipation and quality factors of $10^{12}$, leading to yoctonewton force sensitivity. Trapping the sphere in an optical field enables positioning at less than 1 $\\mu$m from a surface, a regime where exotic new forces may exist. We expect that the proposed system could advance the search for non-Newtonian gravity forces via an enhanced sensitivity of $10^5-10^7$ over current experiments at the 1 $\\mu$m length scale. Moreover, our system may be useful for characterizing other short-range physics such as Casimir forces.
Quantum Gravitational Force Between Polarizable Objects.
Ford, L H; Hertzberg, Mark P; Karouby, J
2016-04-15
Since general relativity is a consistent low energy effective field theory, it is possible to compute quantum corrections to classical forces. Here we compute a quantum correction to the gravitational potential between a pair of polarizable objects. We study two distant bodies and compute a quantum force from their induced quadrupole moments due to two-graviton exchange. The effect is in close analogy to the Casimir-Polder and London-van der Waals forces between a pair of atoms from their induced dipole moments due to two photon exchange. The new effect is computed from the shift in vacuum energy of metric fluctuations due to the polarizability of the objects. We compute the potential energy at arbitrary distances compared to the wavelengths in the system, including the far and near regimes. In the far distance, or retarded, regime, the potential energy takes on a particularly simple form: V(r)=-3987ℏcG^{2}α_{1S}α_{2S}/(4πr^{11}), where α_{1S}, α_{2S} are the static gravitational quadrupole polarizabilities of each object. We provide estimates of this effect. PMID:27127955
Quantum Gravitational Force Between Polarizable Objects
Ford, L H; Karouby, J
2015-01-01
Since general relativity is a consistent low energy effective field theory, it is possible to compute quantum corrections to classical forces. Here we compute a quantum correction to the gravitational potential between a pair of polarizable objects. We study two distant bodies and compute a quantum force from their induced quadrupole moments due to two graviton exchange. The effect is in close analogy to the Casimir-Polder and London-van der Waals forces between a pair of atoms from their induced dipole moments due to two photon exchange. The new effect is computed from the shift in vacuum energy of metric fluctuations due to the polarizability of the objects. We compute the potential energy at arbitrary distances compared to the wavelengths in the system, including the far and near regimes. In the far distance, or retarded, regime, the potential energy takes on a particularly simple form: $V(r)=-3987\\,\\hbar\\,c\\,G^2\\alpha_{1S}\\,\\alpha_{2S}/(4\\,\\pi\\,r^{11})$, where $\\alpha_{1S},\\,\\alpha_{2S}$ are the static gr...
Bezerra, V. B.; Klimchitskaya, G. L.; Mostepanenko, V. M.; Romero, C.
2016-08-01
We propose an experiment for measuring the effective Casimir pressure between two parallel silicon carbide (SiC) plates with aligned nuclear spins. The prospective constraints on an axion-neutron coupling constant for both hadronic and grand unified theory (GUT) axions are calculated using the process of one-axion exchange. For this purpose, a general expression for the additional pressure arising between two polarized plates due to the exchange of one axion between their constituent fermions is derived. We demonstrate that only the polarization component perpendicular to the plates contributes to the pressure. The obtained pressure can be both repulsive and attractive depending on whether the polarizations of both plates are unidirectional or directed in opposite directions. It is shown that although the constraints on an axion-electron coupling obtained in the case of magnetized plates are not competitive, the constraints on an axion-neutron coupling found for plates with polarized nuclear spins are of the same order of magnitude as those obtained previously for the GUT axions alone using the process of two-axion exchange. The proposed experiment allows us also to strengthen the presently known constraints on the axion-neutron coupling constants of GUT axions by using both processes of one- and two-axion exchange.
Fosco, César D
2015-01-01
We study the properties of the classical electromagnetic (EM) radiation produced by two phys- ically different yet closely related systems, which may be regarded as classical analogues of the Dynamical Casimir Effect (DCE). They correspond to two flat, infinite, parallel planes, one of them static and imposing perfect conductor boundary conditions, while the other performs a rigid oscil- latory motion. The systems differ just in the electrical properties of the oscillating plane: one of them is just a planar dipole layer (representing, for instance, a small-width electret). The other, instead, has a dipole layer on the side which faces the static plane, but behaves as a conductor on the other side: this can be used as a representation of a conductor endowed with patch potentials (on the side which faces the conducting plane). We evaluate, in both cases, the dissipative flux of energy between the system and its environment, showing that, at least for small mechanical oscillation amplitudes, it can be written i...
Directory of Open Access Journals (Sweden)
T. A. Puurtinen
2014-12-01
Full Text Available In a previous publication [I. J. Maasilta, AIP Advances 1, 041704 (2011], we discussed the formalism and some computational results for phononic thermal conduction in the suspended membrane geometry for radial heat flow from a central source, which is a common geometry for some low-temperature detectors, for example. We studied the case where only diffusive surface scattering is present, the so called Casimir limit, which can be experimentally relevant at temperatures below ∼ 10 K in typical materials, and even higher for ultrathin samples. Here, we extend our studies to much thinner membranes, obtaining numerical results for geometries which are more typical in experiments. In addition, we interpret the results in terms of the small signal and differential thermal conductance, so that guidelines for designing devices, such as low-temperature bolometric detectors, are more easily obtained. Scaling with membrane dimensions is shown to differ significantly from the bulk scattering, and, in particular, thinning the membrane is shown to lead to a much stronger reduction in thermal conductance than what one would envision from the simplest bulk formulas.
Puurtinen, T. A.; Maasilta, I. J.
2014-12-01
In a previous publication [I. J. Maasilta, AIP Advances 1, 041704 (2011)], we discussed the formalism and some computational results for phononic thermal conduction in the suspended membrane geometry for radial heat flow from a central source, which is a common geometry for some low-temperature detectors, for example. We studied the case where only diffusive surface scattering is present, the so called Casimir limit, which can be experimentally relevant at temperatures below ˜ 10 K in typical materials, and even higher for ultrathin samples. Here, we extend our studies to much thinner membranes, obtaining numerical results for geometries which are more typical in experiments. In addition, we interpret the results in terms of the small signal and differential thermal conductance, so that guidelines for designing devices, such as low-temperature bolometric detectors, are more easily obtained. Scaling with membrane dimensions is shown to differ significantly from the bulk scattering, and, in particular, thinning the membrane is shown to lead to a much stronger reduction in thermal conductance than what one would envision from the simplest bulk formulas.
Energy Technology Data Exchange (ETDEWEB)
Fosco, César D. [Centro Atómico Bariloche, Instituto Balseiro, Comisión Nacional de Energía Atómica, R8402AGP, Bariloche (Argentina); Lombardo, Fernando C., E-mail: lombardo@df.uba.ar [Departamento de Física Juan José Giambiagi, FCEyN UBA and IFIBA CONICET-UBA, Facultad de Ciencias Exactas y Naturales, Ciudad Universitaria, Pabellón I, 1428, Buenos Aires (Argentina)
2015-12-17
We study the properties of the classical electromagnetic radiation produced by two physically different yet closely related systems, which may be regarded as classical analogues of the dynamical Casimir effect. They correspond to two flat, infinite, parallel planes, one of them static and imposing perfect-conductor boundary conditions, while the other performs a rigid oscillatory motion. The systems differ just in the electrical properties of the oscillating plane: one of them is just a planar dipole layer (representing, for instance, a small-width electret). The other, instead, has a dipole layer on the side which faces the static plane, but behaves as a conductor on the other side: this can be used as a representation of a conductor endowed with patch potentials (on the side which faces the conducting plane). We evaluate, in both cases, the dissipative flux of energy between the system and its environment, showing that, at least for small mechanical oscillation amplitudes, it can be written in terms of the dipole layer autocorrelation function. We show that there are resonances as a function of the frequency of the mechanical oscillation.
Energy Technology Data Exchange (ETDEWEB)
Fosco, Cesar D. [Comision Nacional de Energia Atomica, Centro Atomico Bariloche, Instituto Balseiro, Bariloche (Argentina); Lombardo, Fernando C. [Ciudad Universitaria, Departamento de Fisica Juan Jose Giambiagi, FCEyN UBA y IFIBA CONICET-UBA, Facultad de Ciencias Exactas y Naturales, Buenos Aires (Argentina)
2015-12-15
We study the properties of the classical electromagnetic radiation produced by two physically different yet closely related systems, which may be regarded as classical analogues of the dynamical Casimir effect. They correspond to two flat, infinite, parallel planes, one of them static and imposing perfect-conductor boundary conditions, while the other performs a rigid oscillatory motion. The systems differ just in the electrical properties of the oscillating plane: one of them is just a planar dipole layer (representing, for instance, a small-width electret). The other, instead, has a dipole layer on the side which faces the static plane, but behaves as a conductor on the other side: this can be used as a representation of a conductor endowed with patch potentials (on the side which faces the conducting plane). We evaluate, in both cases, the dissipative flux of energy between the system and its environment, showing that, at least for small mechanical oscillation amplitudes, it can be written in terms of the dipole layer autocorrelation function. We show that there are resonances as a function of the frequency of the mechanical oscillation. (orig.)
De vette jaren: de Commissie-Casimir en het Nederlandse wetenschapsbeleid 1957-1970
Directory of Open Access Journals (Sweden)
David Baneke
2012-11-01
Full Text Available The Years of Abundance: the Casimir Committee and Dutch Science Policy 1957–1970 In October 1958, a committee of six prominent Dutch scientists and industrial managers presented a brief report in which they requested a major increase of the science budget. This report has been described as a turning point in the history of science in the Netherlands, signaling the beginning of a decade of rapid growth of funding for ‘pure’ research. Surprisingly little is known about the backgrounds of this report, however. In this paper, I analyze its origin, its relation to contemporary higher education policy, and its consequences. As it turns out, the report was less revolutionary than is usually assumed: it mostly reinforced developments that had already begun earlier. Furthermore, Sputnik and the Cold War were not as important as is often claimed. This paper also suggests a reinterpretation of the justification of the government spending on academic research after the Second World War. Producing skilled researchers for industry was at least as important as produc- ing new knowledge.
International Nuclear Information System (INIS)
Conservation laws in ideal gas dynamics and magnetohydrodynamics (MHD) associated with fluid relabeling symmetries are derived using Noether's first and second theorems. Lie dragged invariants are discussed in terms of the MHD Casimirs. A nonlocal conservation law for fluid helicity applicable for a non-barotropic fluid involving Clebsch variables is derived using Noether's theorem, in conjunction with a fluid relabeling symmetry and a gauge transformation. A nonlocal cross helicity conservation law involving Clebsch potentials, and the MHD energy conservation law are derived by the same method. An Euler–Poincaré variational approach is also used to derive conservation laws associated with fluid relabeling symmetries using Noether's second theorem. (paper)
Directory of Open Access Journals (Sweden)
Michael A. Persinger
2015-09-01
Full Text Available The ~1.5 × 10−20 J which is considered a universal quantity and is associated with the movement of protons in water also relates to the ratio of the magnetic moment of a proton divided by its unit charge, multiplied by viscosity and applied over the O-H distance. There is quantitative evidence that thixotropy, the “spontaneous” increased viscosity in water when undisturbed, originates from the transformation of virtual particles or vacuum oscillations to real states through conversion of Casimir-magnetic energies that involve the frequency of the neutral hydrogen line and the upper bound threshold value for intergalactic magnetic fields. The results indicate that ½ of a single electron orbit is real (particle and the other ½ is virtual (wave. The matter equivalent per s for virtual-to-real states for electrons in 1 mL of water with a neutral pH is consistent with the numbers of protons (H+ and the measured range of molecules in the coherent domains for both width and duration of growth and is similar to widths of intergalactic dust grains from which planets and stars may condense. The de Broglie momentum for the lower boundary of the width of coherent domains multiplied by the fine structure velocity of an electron is concurrent with the quantum when one proton is being removed from another and when the upper boundary of the rest mass of a photon is transformed by the product of velocities for putative “entanglement” and light. Theoretical and experimental results indicate that components of thixotropy, such as specific domains of intercalated water molecules, could display excess correlations over very large distances. Because the energies of the universal quantity and water converge it may be a special conduit for discrete transformations from virtual to real states.
The Casimir Effect from the Point of View of Algebraic Quantum Field Theory
Dappiaggi, Claudio; Nosari, Gabriele; Pinamonti, Nicola
2016-06-01
We consider a region of Minkowski spacetime bounded either by one or by two parallel, infinitely extended plates orthogonal to a spatial direction and a real Klein-Gordon field satisfying Dirichlet boundary conditions. We quantize these two systems within the algebraic approach to quantum field theory using the so-called functional formalism. As a first step we construct a suitable unital ∗-algebra of observables whose generating functionals are characterized by a labelling space which is at the same time optimal and separating and fulfils the F-locality property. Subsequently we give a definition for these systems of Hadamard states and we investigate explicit examples. In the case of a single plate, it turns out that one can build algebraic states via a pull-back of those on the whole Minkowski spacetime, moreover inheriting from them the Hadamard property. When we consider instead two plates, algebraic states can be put in correspondence with those on flat spacetime via the so-called method of images, which we translate to the algebraic setting. For a massless scalar field we show that this procedure works perfectly for a large class of quasi-free states including the Poincaré vacuum and KMS states. Eventually Wick polynomials are introduced. Contrary to the Minkowski case, the extended algebras, built in globally hyperbolic subregions can be collected in a global counterpart only after a suitable deformation which is expressed locally in terms of a *-isomorphism. As a last step, we construct explicitly the two-point function and the regularized energy density, showing, moreover, that the outcome is consistent with the standard results of the Casimir effect.
Occupational Outlook Quarterly, 2012
2012-01-01
The labor force is the number of people ages 16 or older who are either working or looking for work. It does not include active-duty military personnel or the institutionalized population, such as prison inmates. Determining the size of the labor force is a way of determining how big the economy can get. The size of the labor force depends on two…
Revivals and Casimir energy for a free Maxwell field (spin-1 singleton) on R x S^d for odd d
Dowker, J S
2016-01-01
Earlier work on quantum revivals is extended to Maxwell fields (aka spin-one singletons). An evaluation of the Casimir energy on the generalised Einstein universe is also done to illustrate the utility of the Barnes zeta-function and generalised Bernoulli polynomials. Contact is made with some recent calculations in AdS/CFT.
Casimir energy of the Nambu-Goto string with Gauss-Bonnet term and point-like masses at the ends
Hadasz, L
1999-01-01
We calculate (using zeta function regularization) the Casimir energy of the rotating Nambu-Goto string with the Gauss-Bonnet term in the action and point-like masses at the ends. The resulting value turns out to be negative for all values of the parameters of the model.
在周期边界条件下的类Casimir力%Casimir-like effect with periodic boundary conditions
Institute of Scientific and Technical Information of China (English)
李长松; 张玥; 郑泰玉; 姜文英; 潘淑梅
2013-01-01
The Casimir-like effect is investigated in dilute Bose-Einstein Condensation at zero-temperature between the two parallel plates with periodic boundary conditions. Obtained the much smaller Bogoliubov corrections due to the nonlinearity of the Bogoliubov dispersion relation. In the calculation, any ultraviolet cut-off parameter was not introduced. These results will will help us further understand the physical effect in the Bose-Einstein condensed body and provide certain reference value to Casimir effect and the Bose-Einstein Condensation experimental study.%研究了在绝对零度下2个平行板之间周期边界条件下均匀稀释玻色爱因斯坦凝聚体中的类Casimir力,得到Bogoliubov色散关系的高阶修正项.计算中没有引入任何截断函数,获得了有限的结果.该结果有助于进一步了解玻色爱因斯坦凝聚体的物理机制,并且对Casimir效应和玻色-爱因斯坦凝聚的实验研究具有一定的参考价值.
Pejhan, Hamed
2016-01-01
In a previous work [S. Rahbardehghan et al. in Phys. Lett. B 750, 627 (2015)], we considered a simple brane-world model; a single $4$-dimensional brane embedded in a $5$-dimensional de Sitter (dS) space-time. Then, by including a conformally coupled scalar field in the bulk, we studied the induced Casimir energy-momentum tensor. Technically, the Krein-Gupta-Bleuler (KGB) quantization scheme as a covariant and renormalizable quantum field theory in dS space was used to perform the calculations. In the present paper, we generalize this study to a less idealized, but physically motivated, scenario, namely we consider Friedmann-Robertson-Walker (FRW) space-time which behaves asymptotically as a dS space-time. More precisely, we evaluate Casimir energy-momentum tensor for a system with two $D$-dimensional curved branes on background of $D+1$-dimensional FRW space-time with negative spatial curvature and a bulk conformally coupled scalar field that satisfies Dirichlet boundary condition on the branes.
Capture de forces à atomes piégés dans un réseau optique : caractérisation des performances
Hilico, Adèle
2014-01-01
The thesis presents the set up of the second version of the experiment FORCA-G (CAsimir FORce and Gravitation at short range). The purpose of this experiment is the measurement of short-range interactions between an atom and a massive surface. The measurement is realised thanks to atom interferometers using atoms trapped in a 1D vertical optical lattice. The energy levels of atoms in such a trap are shifted from lattice site to another by the force we aim at measuring. We move the atoms from ...
Forces between a partially coherent fluctuating source and a magnetodielectric particle
Auñon, Juan Miguel
2013-01-01
We address the forces exerted by the electromagnetic ?eld emitted by a planar uctuating source on dielectric particles that have arose much interest because of their recently shown magnetodielectric behavior. In this context, we analyze as a particular case the modi?cation of the Casimir and Van der Waals forces. We study the e?ect of the source coherence length as well as the interplay between the force from the radiated ?eld and that from the electric and magnetic dipoles induced on the particle. This allows a control of these interactions as well as of the weight and interference e?ects between the ?elds from both kinds of induced dipoles, in particular when large changes in their di?erential scattering cross section occur due to Kerker minimum forward or zero backward conditions; thus opening new paths to nanoparticle ensembling and manipulation. The influence of surface waves of the source is also studied.
A scheme for solving the plane-plane challenge in force measurements at the nanoscale.
Siria, Alessandro; Huant, Serge; Auvert, Geoffroy; Comin, Fabio; Chevrier, Joel
2010-05-19
Non-contact interaction between two parallel flat surfaces is a central paradigm in sciences. This situation is the starting point for a wealth of different models: the capacitor description in electrostatics, hydrodynamic flow, thermal exchange, the Casimir force, direct contact study, third body confinement such as liquids or films of soft condensed matter. The control of parallelism is so demanding that no versatile single force machine in this geometry has been proposed so far. Using a combination of nanopositioning based on inertial motors, of microcrystal shaping with a focused-ion beam (FIB) and of accurate in situ and real-time control of surface parallelism with X-ray diffraction, we propose here a "gedanken" surface-force machine that should enable one to measure interactions between movable surfaces separated by gaps in the micrometer and nanometer ranges.
Controlling dispersion forces between small particles with artificially created random light fields
Bruegger, Georges; Scheffold, Frank; Saenz, Juan Jose
2015-01-01
Appropriate combinations of laser beams can be used to trap and manipulate small particles with "optical tweezers" as well as to induce significant "optical binding" forces between particles. These interaction forces are usually strongly anisotropic depending on the interference landscape of the external fields. This is in contrast with the familiar isotropic, translationally invariant, van der Waals and, in general, Casimir-Lifshitz interactions between neutral bodies arising from random electromagnetic waves generated by equilibrium quantum and thermal fluctuations. Here we show, both theoretically and experimentally, that dispersion forces between small colloidal particles can also be induced and controlled using artificially created fluctuating light fields. Using optical tweezers as gauge, we present experimental evidence for the predicted isotropic attractive interactions between dielectric microspheres induced by laser-generated, random light fields. These light induced interactions open a path towards...
A Scheme for Solving the Plane–Plane Challenge in Force Measurements at the Nanoscale
Directory of Open Access Journals (Sweden)
Comin Fabio
2010-01-01
Full Text Available Abstract Non-contact interaction between two parallel flat surfaces is a central paradigm in sciences. This situation is the starting point for a wealth of different models: the capacitor description in electrostatics, hydrodynamic flow, thermal exchange, the Casimir force, direct contact study, third body confinement such as liquids or films of soft condensed matter. The control of parallelism is so demanding that no versatile single force machine in this geometry has been proposed so far. Using a combination of nanopositioning based on inertial motors, of microcrystal shaping with a focused-ion beam (FIB and of accurate in situ and real-time control of surface parallelism with X-ray diffraction, we propose here a “gedanken” surface-force machine that should enable one to measure interactions between movable surfaces separated by gaps in the micrometer and nanometer ranges.
Sanders, David
2007-01-01
A young child can explore and learn and compensate for unknown dynamics by prodding, pushing, touching, grasping and feeling. Force sensing and software research could soon allow artificial mechanisms to do the same. Force sensing has its roots in strain gauges, piezoelectrics, Wheatstone bridges, automation, robotics, grippers and virtual reality. That force sensing research has now become commonplace and has expanded from those roots to include so much more: video games, athletic equipment,...
Without the strong force, there could be no life. The carbon in living matter is synthesised in stars via the strong force. Lighter atomic nuclei become bound together in a process called nuclear fusion. A minor change in this interaction would make life impossible. As its name suggests, the strong force is the most powerful of the 4 forces, yet its sphere of influence is limited to within the atomic nucleus. Indeed it is the strong force that holds together the quarks inside the positively charged protons. Without this glue, the quarks would fly apart repulsed by electromagnetism. In fact, it is impossible to separate 2 quarks : so much energy is needed, that a second pair of quarks is produced. Text for the interactive: Can you pull apart the quarks inside a proton?
Without the weak force, the sun wouldn't shine. The weak force causes beta decay, a form of radioactivity that triggers nuclear fusion in the heart of the sun. The weak force is unlike other forces: it is characterised by disintegration. In beta decay, a down quark transforms into an up quark and an electron is emitted. Some materials are more radioactive than others because the delicate balance between the strong force and the weak force varies depending on the number of particles in the atomic nucleus. We live in the midst of a natural radioactive background that varies from region to region. For example, in Cornwall where there is a lot of granite, levels of background radiation are much higher than in the Geneva region. Text for the interactive: Move the Geiger counter to find out which samples are radioactive - you may be surprised. It is the weak force that is responsible for the Beta radioactivity here. The electrons emitted do not cross the plastic cover. Why do you think there is some detected radioa...
Institute of Scientific and Technical Information of China (English)
Yulong Yan; Baozeng Yue∗
2016-01-01
The stability of partly liquid filled spacecraft with flexible attachment was investigated in this paper. Liquid sloshing dynamics was simplified as the spring–mass model, and flexible attachment was modeled as the linear shearing beam. The dynamic equations and Hamiltonian of the coupled spacecraft system were given by analyzing the rigid body, liquid fuel, and flexible appendage. Nonlinear stability conditions of the coupled spacecraft system were derived by computing the variation of Casimir function which was added to the Hamiltonian. The stable region of the parameter space was given and validated by numerical computation. Related results suggest that the change of inertia matrix, the length of flexible attachment, spacecraft spinning rate, and filled ratio of liquid fuel tank have strong influence on the stability of the spacecraft system.
International Nuclear Information System (INIS)
We study the Casimir energy density of the Klein-Gordon-field in the case of two static geometries. We model the effect by coupling the free quantum field to a static classical scalar field. We work out the dependence on the coupling λ, including the limit λ=∞ (Dirichlet boundary condition). The chosen geometries are described by a δ-funktion (σ(x)=δ(x3)) and a step function of finite height (σ(x)(1)/(2ε)1[ε,ε](x3)), respectively. In the area outside the support of the background the density energy converges; calculations for the distorted area lead to divergent surface terms. (orig.)
Chernodub, M N
2012-01-01
Recently, we have demonstrated that for a certain class of Casimir-type systems ("devices") the energy of zero-point vacuum fluctuations reaches its global minimum when the device rotates about certain axis rather than remains static. This rotational vacuum effect may lead to emergence of permanently rotating objects - philosophically similar to "time crystals" proposed recently by Shapere and Wilczek in classical and quantum mechanical systems - provided the negative rotational energy of zero-point fluctuations cancels the positive rotational energy of the device itself. In this paper we show that for massless electrically charged particles the rotational vacuum effect should be drastically (astronomically) enhanced in the presence of magnetic field. As an illustration, we show that in a background of experimentally available magnetic fields the zero-point energy of massless excitations in rotating torus-shaped doped carbon nanotubes may indeed overwhelm the classical energy of rotation for certain angular f...
Mostepanenko, V M; Caride, A O; Klimchitskaya, G L; Zanette, S I
2006-01-01
The Casimir-Polder and van der Waals interactions between an atom and a flat cavity wall are investigated under the influence of real conditions including the dynamic polarizability of the atom, actual conductivity of the wall material and nonzero temperature of the wall. The cases of different atoms near metal and dielectric walls are considered. It is shown that to obtain accurate results for the atom-wall interaction at short separations, one should use the complete tabulated optical data for the complex refractive index of the wall material and the accurate dynamic polarizability of an atom. At relatively large separations in the case of a metal wall, one may use the plasma model dielectric function to describe the dielectric properties of wall material. The obtained results are important for the theoretical interpretation of experiments on quantum reflection and Bose-Einstein condensation.
Chernodub, M. N.
2013-01-01
Recently, we have demonstrated that for a certain class of Casimir-type systems (“devices”) the energy of zero-point vacuum fluctuations reaches its global minimum when the device rotates about a certain axis rather than remains static. This rotational vacuum effect may lead to the emergence of permanently rotating objects provided the negative rotational energy of zero-point fluctuations cancels the positive rotational energy of the device itself. In this paper, we show that for massless electrically charged particles the rotational vacuum effect should be drastically (astronomically) enhanced in the presence of a magnetic field. As an illustration, we show that in a background of experimentally available magnetic fields the zero-point energy of massless excitations in rotating torus-shaped doped carbon nanotubes may indeed overwhelm the classical energy of rotation for certain angular frequencies so that the permanently rotating state is energetically favored. The suggested “zero-point-driven” devices—which have no internally moving parts—correspond to a perpetuum mobile of a new, fourth kind: They do not produce any work despite the fact that their equilibrium (ground) state corresponds to a permanent rotation even in the presence of an external environment. We show that our proposal is consistent with the laws of thermodynamics.
Elizalde, E; Saharian, A A
2011-01-01
We investigate the fermionic condensate and the vacuum expectation value of the energy-momentum tensor for a massive fermionic field in the geometry of two parallel plate on the background of Minkowski spacetime with an arbitrary number of toroidally compactified spatial dimensions, in the presence of a constant gauge field. Bag boundary conditions are imposed on the plates and periodicity conditions with arbitrary phases are considered along the compact dimensions. The boundary induced parts in the fermionic condensate and the vacuum energy density are negative, with independence of the phases in the periodicity conditions and of the value of the gauge potential. Interaction forces between the plates are thus always attractive. However, in physical situations where the quantum field is confined to the region between the plates, the pure topological part contributes as well, and then the resulting force can be either attractive or repulsive, depending on the specific phases encoded in the periodicity conditio...
Casimir interaction of rodlike particles in a two-dimensional critical system
Eisenriegler, E.; Burkhardt, T. W.
2016-09-01
We consider the fluctuation-induced interaction of two thin, rodlike particles, or "needles," immersed in a two-dimensional critical fluid of Ising symmetry right at the critical point. Conformally mapping the plane containing the needles onto a simpler geometry in which the stress tensor is known, we analyze the force and torque between needles of arbitrary length, separation, and orientation. For infinite and semi-infinite needles we utilize the mapping of the plane bounded by the needles onto the half plane, and for two needles of finite length we use the mapping onto an annulus. For semi-infinite and infinite needles the force is expressed in terms of elementary functions, and we also obtain analytical results for the force and torque between needles of finite length with separation much greater than their length. Evaluating formulas in our approach numerically for several needle geometries and surface universality classes, we study the full crossover from small to large values of the separation to length ratio. In these two limits the numerical results agree with results for infinitely long needles and with predictions of the small-particle operator expansion, respectively.
Danilova, N. P.
2015-09-01
From the Editorial Board. In a brief followup to the talk by E I Kats on "Van der Waals, Casimir, and Lifshitz forces in soft matter" (see pp. 892 - 896 of this issue) at the E M Lifshitz centennial session of the Physical Sciences Division of the Russian Academy of Sciences, an interesting and instructive story was told by Nina Petrovna Danilova (Department of Low Temperature Physics and Superconductivity, Faculty of Physics, Moscow State University) of how E M Lifshitz was enlisted to explain I I Abrikosova's and B V Derjaguin's experimental results. The Editorial Board of Uspekhi Fizicheskikh Nauk (UFN) [Physics-Uspekhi] journal found the story appropriate to be published in the "Letters to the Editor" section of UFN in a jubilee selection of works marking the centennial of E M Lifshitz' birth.
Casimir densities for two concentric spherical shells in the global monopole spacetime
Saharian, A A
2003-01-01
The quantum vacuum effects are investigated for a massive scalar field with general curvature coupling and obeying the Robin boundary conditions given on two concentric spherical shells with radii $a $ and $b$ in the $D+1$-dimensional global monopole background. The expressions are derived for the Wightman function, the vacuum expectation values of the field square, the vacuum energy density, radial and azimuthal stress components in the region between the shells. A regularization procedure is carried out by making use of the generalized Abel-Plana formula for the series over zeros of combinations of the cylinder functions. This formula allows us to extract from the vacuum expectation values the parts due to a single sphere on background of the global monopole gravitational field, and to present the "interference" parts in terms of exponentially convergent integrals, useful, in particular, for numerical evaluations. The vacuum forces acting on the boundaries are presented as a sum of the self--action and inte...
Sun, Zhelin; Wang, Deli; Xiang, Jie
2014-11-25
Spontaneous attractions between free-standing nanostructures have often caused adhesion or stiction that affects a wide range of nanoscale devices, particularly nano/microelectromechanical systems. Previous understandings of the attraction mechanisms have included capillary force, van der Waals/Casimir forces, and surface polar charges. However, none of these mechanisms universally applies to simple semiconductor structures such as silicon nanowire arrays that often exhibit bunching or adhesions. Here we propose a simple capacitive force model to quantitatively study the universal spontaneous attraction that often causes stiction among semiconductor or metallic nanostructures such as vertical nanowire arrays with inevitably nonuniform size variations due to fabrication. When nanostructures are uniform in size, they share the same substrate potential. The presence of slight size differences will break the symmetry in the capacitive network formed between the nanowires, substrate, and their environment, giving rise to electrostatic attraction forces due to the relative potential difference between neighboring wires. Our model is experimentally verified using arrays of vertical silicon nanowire pairs with varied spacing, diameter, and size differences. Threshold nanowire spacing, diameter, or size difference between the nearest neighbors has been identified beyond which the nanowires start to exhibit spontaneous attraction that leads to bridging when electrostatic forces overcome elastic restoration forces. This work illustrates a universal understanding of spontaneous attraction that will impact the design, fabrication, and reliable operation of nanoscale devices and systems. PMID:25329454
Directory of Open Access Journals (Sweden)
Ya-Pu Zhao
2007-11-01
Full Text Available The influence of damping on the dynamical behavior of the electrostaticparallel-plate and torsional actuators with the van der Waals (vdW or Casimir force(torque is presented. The values of the pull-in parameters and the number of theequilibrium points do not change whether there is damping or not. The ability ofequilibrium points is varied with the appearance of damping. One equilibrium point is anunstable saddle with a different damping coefficient, the other equilibrium point is astable node when the damping coefficient is greater than some critical value, andotherwise it is a stable focus. Then there are two heteroclinic orbits passing from theunstable saddle point to the stable node or focus.
Arzura Idris
2012-01-01
This paper analyzes the phenomenon of “forced migration” in Malaysia. It examines the nature of forced migration, the challenges faced by Malaysia, the policy responses and their impact on the country and upon the forced migrants. It considers forced migration as an event hosting multifaceted issues related and relevant to forced migrants and suggests that Malaysia has been preoccupied with the issue of forced migration movements. This is largely seen in various responses invoked from Malaysi...
Stefanescu, Dan Mihai
2011-01-01
Part I introduces the basic ""Principles and Methods of Force Measurement"" acording to a classification into a dozen of force transducers types: resistive, inductive, capacitive, piezoelectric, electromagnetic, electrodynamic, magnetoelastic, galvanomagnetic (Hall-effect), vibrating wires, (micro)resonators, acoustic and gyroscopic. Two special chapters refer to force balance techniques and to combined methods in force measurement. Part II discusses the ""(Strain Gauge) Force Transducers Components"", evolving from the classical force transducer to the digital / intelligent one, with the inco
Nanonet Force Microscopy for Measuring Cell Forces.
Sheets, Kevin; Wang, Ji; Zhao, Wei; Kapania, Rakesh; Nain, Amrinder S
2016-07-12
The influence of physical forces exerted by or felt by cells on cell shape, migration, and cytoskeleton arrangement is now widely acknowledged and hypothesized to occur due to modulation of cellular inside-out forces in response to changes in the external fibrous environment (outside-in). Our previous work using the non-electrospinning Spinneret-based Tunable Engineered Parameters' suspended fibers has revealed that cells are able to sense and respond to changes in fiber curvature and structural stiffness as evidenced by alterations to focal adhesion cluster lengths. Here, we present the development and application of a suspended nanonet platform for measuring C2C12 mouse myoblast forces attached to fibers of three diameters (250, 400, and 800 nm) representing a wide range of structural stiffness (3-50 nN/μm). The nanonet force microscopy platform measures cell adhesion forces in response to symmetric and asymmetric external perturbation in single and cyclic modes. We find that contractility-based, inside-out forces are evenly distributed at the edges of the cell, and that forces are dependent on fiber structural stiffness. Additionally, external perturbation in symmetric and asymmetric modes biases cell-fiber failure location without affecting the outside-in forces of cell-fiber adhesion. We then extend the platform to measure forces of (1) cell-cell junctions, (2) single cells undergoing cyclic perturbation in the presence of drugs, and (3) cancerous single-cells transitioning from a blebbing to a pseudopodial morphology. PMID:27410747
Force propagation and force generation in cells.
Jonas, Oliver; Duschl, Claus
2010-09-01
Determining how forces are produced by and propagated through the cytoskeleton (CSK) of the cell is of great interest as dynamic processes of the CSK are intimately correlated with many molecular signaling pathways. We are presenting a novel approach for integrating measurements on cell elasticity, transcellular force propagation, and cellular force generation to obtain a comprehensive description of dynamic and mechanical properties of the CSK under force loading. This approach uses a combination of scanning force microscopy (SFM) and Total Internal Reflection Fluorescence (TIRF) microscopy. We apply well-defined loading schemes onto the apical cell membrane of fibroblasts using the SFM and simultaneously use TIRF microscopy to image the topography of the basal cell membrane. The locally distinct changes of shape and depth of the cytoskeletal imprints onto the basal membrane are interpreted as results of force propagation through the cytoplasm. This observation provides evidence for the tensegrity model and demonstrates the usefulness of our approach that does not depend on potentially disturbing marker compounds. We confirm that the actin network greatly determines cell stiffness and represents the substrate that mediates force transduction through the cytoplasm of the cell. The latter is an essential feature of tensegrity. Most importantly, our new finding that, both intact actin and microtubule networks are required for enabling the cell to produce work, can only be understood within the framework of the tensegrity model. We also provide, for the first time, a direct measurement of the cell's mechanical power output under compression at two femtowatts. PMID:20607861
Directory of Open Access Journals (Sweden)
Arzura Idris
2012-06-01
Full Text Available This paper analyzes the phenomenon of “forced migration” in Malaysia. It examines the nature of forced migration, the challenges faced by Malaysia, the policy responses and their impact on the country and upon the forced migrants. It considers forced migration as an event hosting multifaceted issues related and relevant to forced migrants and suggests that Malaysia has been preoccupied with the issue of forced migration movements. This is largely seen in various responses invoked from Malaysia due to “south-south forced migration movements.” These responses are, however, inadequate in terms of commitment to the international refugee regime. While Malaysia did respond to economic and migration challenges, the paper asserts that such efforts are futile if she ignores issues critical to forced migrants.
Hydrophobic Forces in Flotation
Pazhianur, Rajesh R
1999-01-01
An atomic force microscope (AFM) has been used to conduct force measurements to better understand the role of hydrophobic forces in flotation. The force measurements were conducted between a flat mineral substrate and a hydrophobic glass sphere in aqueous solutions. It is assumed that the hydrophobic glass sphere may simulate the behavior of air bubbles during flotation. The results may provide information relevant to the bubble-particle interactions occurring during flotation. The glass ...
Debunking Coriolis Force Myths
Shakur, Asif
2014-01-01
Much has been written and debated about the Coriolis force. Unfortunately, this has done little to demystify the paradoxes surrounding this fictitious force invoked by an observer in a rotating frame of reference. It is the purpose of this article to make another valiant attempt to slay the dragon of the Coriolis force! This will be done without…
International Nuclear Information System (INIS)
A force transducer for measuring lift and drag coefficients for a circular cylinder in turbulent water flow is presented. In addition to describing the actual design and construction of the strain-gauged force- ring based transducer, requirements for obtained valid fluid force test data are discussed, and pertinent flow test experience is related
Static forces in d=2+1 SU(N) gauge theories
Energy Technology Data Exchange (ETDEWEB)
Meyer, H.B.
2006-07-15
Using a three-level algorithm we perform a high-precision lattice computation of the static force up to 1fm in the 2+1 dimensional SU(5) gauge theory. Discretization errors and the continuum limit are discussed in detail. By comparison with existing SU(2) and SU(3) data it is found that {sigma}r{sup 2}{sub 0}=1.65-({pi})/(24) holds at an accuracy of 1% for all N{>=}2, where r{sub 0} is the Sommer reference scale. The effective central charge c(r) is obtained and an intermediate distance r{sub s} is defined via the property c(r{sub s})=({pi})/(24). It separates in a natural way the short-distance regime governed by perturbation theory from the long-distance regime described by an effective string theory. The ratio {tau}{sub s}/{tau}{sub 0} decreases significantly from SU(2) to SU(3) to SU(5), where r{sub s}
Static forces in d=2+1 SU(N) gauge theories
International Nuclear Information System (INIS)
Using a three-level algorithm we perform a high-precision lattice computation of the static force up to 1fm in the 2+1 dimensional SU(5) gauge theory. Discretization errors and the continuum limit are discussed in detail. By comparison with existing SU(2) and SU(3) data it is found that σr20=1.65-(π)/(24) holds at an accuracy of 1% for all N≥2, where r0 is the Sommer reference scale. The effective central charge c(r) is obtained and an intermediate distance rs is defined via the property c(rs)=(π)/(24). It separates in a natural way the short-distance regime governed by perturbation theory from the long-distance regime described by an effective string theory. The ratio τs/τ0 decreases significantly from SU(2) to SU(3) to SU(5), where rs0. We give a preliminary estimate of its value in the large-N limit. The static force in the smallest representation of N-ality 2, which tends to the k=2 string tension as r→∞, is also computed up to 0.7 fm. The deviation from Casimir scaling is positive and grows from 0.1% to 1% in that range. (Orig.)
Hansen, J.; Sato, M.; Ruedy, R.; Nazarenko, L.; Lacis, A.; Schmidt, G. A.; Russell, G.; Aleinov, I.; Bauer, M.; Bauer, S.; Bell, N.; Cairns, B.; Canuto, V.; Chandler, M.; Cheng, Y.; Del Genio, A.; Faluvegi, G.; Fleming, E.; Friend, A.; Hall, T.; Jackman, C.; Kelley, M.; Kiang, N.; Koch, D.; Lean, J.; Lerner, J.; Lo, K.; Menon, S.; Miller, R.; Minnis, P.; Novakov, T.; Oinas, V.; Perlwitz, Ja.; Perlwitz, Ju.; Rind, D.; Romanou, A.; Shindell, D.; Stone, P.; Sun, S.; Tausnev, N.; Thresher, D.; Wielicki, B.; Wong, T.; Yao, M.; Zhang, S.
2005-09-01
We use a global climate model to compare the effectiveness of many climate forcing agents for producing climate change. We find a substantial range in the "efficacy" of different forcings, where the efficacy is the global temperature response per unit forcing relative to the response to CO2 forcing. Anthropogenic CH4 has efficacy ˜110%, which increases to ˜145% when its indirect effects on stratospheric H2O and tropospheric O3 are included, yielding an effective climate forcing of ˜0.8 W/m2 for the period 1750-2000 and making CH4 the largest anthropogenic climate forcing other than CO2. Black carbon (BC) aerosols from biomass burning have a calculated efficacy ˜58%, while fossil fuel BC has an efficacy ˜78%. Accounting for forcing efficacies and for indirect effects via snow albedo and cloud changes, we find that fossil fuel soot, defined as BC + OC (organic carbon), has a net positive forcing while biomass burning BC + OC has a negative forcing. We show that replacement of the traditional instantaneous and adjusted forcings, Fi and Fa, with an easily computed alternative, Fs, yields a better predictor of climate change, i.e., its efficacies are closer to unity. Fs is inferred from flux and temperature changes in a fixed-ocean model run. There is remarkable congruence in the spatial distribution of climate change, normalized to the same forcing Fs, for most climate forcing agents, suggesting that the global forcing has more relevance to regional climate change than may have been anticipated. Increasing greenhouse gases intensify the Hadley circulation in our model, increasing rainfall in the Intertropical Convergence Zone (ITCZ), Eastern United States, and East Asia, while intensifying dry conditions in the subtropics including the Southwest United States, the Mediterranean region, the Middle East, and an expanding Sahel. These features survive in model simulations that use all estimated forcings for the period 1880-2000. Responses to localized forcings, such
Hernández-Trujillo, Jesús; Cortés-Guzmán, Fernando; Fang, De-Chai; Bader, Richard F W
2007-01-01
Chemistry is determined by the electrostatic forces acting within a collection of nuclei and electrons. The attraction of the nuclei for the electrons is the only attractive force in a molecule and is the force responsible for the bonding between atoms. This is the attractive force acting on the electrons in the Ehrenfest force and on the nuclei in the Feynman force, one that is countered by the repulsion between the electrons in the former and by the repulsion between the nuclei in the latter. The virial theorem relates these forces to the energy changes resulting from interactions between atoms. All bonding, as signified by the presence of a bond path, has a common origin in terms of the mechanics determined by the Ehrenfest, Feynman and virial theorems. This paper is concerned in particular with the mechanics of interaction encountered in what are classically described as 'nonbonded interactions'--are atoms that 'touch' bonded or repelling one another? PMID:17328425
Hernández-Trujillo, Jesús; Cortés-Guzmán, Fernando; Fang, De-Chai; Bader, Richard F W
2007-01-01
Chemistry is determined by the electrostatic forces acting within a collection of nuclei and electrons. The attraction of the nuclei for the electrons is the only attractive force in a molecule and is the force responsible for the bonding between atoms. This is the attractive force acting on the electrons in the Ehrenfest force and on the nuclei in the Feynman force, one that is countered by the repulsion between the electrons in the former and by the repulsion between the nuclei in the latter. The virial theorem relates these forces to the energy changes resulting from interactions between atoms. All bonding, as signified by the presence of a bond path, has a common origin in terms of the mechanics determined by the Ehrenfest, Feynman and virial theorems. This paper is concerned in particular with the mechanics of interaction encountered in what are classically described as 'nonbonded interactions'--are atoms that 'touch' bonded or repelling one another?
Energy Technology Data Exchange (ETDEWEB)
Bialynicki-Birula, I. [Center for Theoretical Physics, Polish Academy of Sciences, Warsaw (Poland); Abt. fuer Quantenphysik, Univ. Ulm, Ulm (Germany); Cirone, M.A.; Straub, F.; Schleich, W.P. [Abt. fuer Quantenphysik, Univ. Ulm, Ulm (Germany); Dahl, J.P. [Abt. fuer Quantenphysik, Univ. Ulm, Ulm (Germany); Chemical Physics, Dept. of Chemistry, Technical Univ. of Denmark, Lyngby (Denmark); Seligman, T.H. [Centro de Ciencias Fisicas, Univ. of Mexico (UNAM), Cuernavaca (Mexico)
2002-07-01
We present Heisenberg's equation of motion for the radial variable of a free non-relativistic particle in D dimensions. The resulting radial force consists of three contributions: (i) the quantum fictitious force which is either attractive or repulsive depending on the number of dimensions, (ii) a singular quantum force located at the origin, and (iii) the centrifugal force associated with non-vanishing angular momentum. Moreover, we use Heisenberg's uncertainty relation to introduce a lower bound for the kinetic energy of an ensemble of neutral particles. This bound is quadratic in the number of atoms and can be traced back to the repulsive quantum fictitious potential. All three forces arise for a free particle: ''Force without force''. (orig.)
Nonlinear Dynamic Force Spectroscopy
Björnham, Oscar
2016-01-01
Dynamic force spectroscopy (DFS) is an experimental technique that is commonly used to assess information of the strength, energy landscape, and lifetime of noncovalent bio-molecular interactions. DFS traditionally requires an applied force that increases linearly with time so that the bio-complex under investigation is exposed to a constant loading rate. However, tethers or polymers can modulate the applied force in a nonlinear regime. For example, bacterial adhesion pili and polymers with worm-like chain properties are examples of structures that show nonlinear force responses. In these situations, the theory for traditional DFS cannot be readily applied. In this work we expand the theory for DFS to also include nonlinear external forces while still maintaining compatibility with the linear DFS theory. To validate the theory we modeled a bio-complex expressed on a stiff, an elastic and a worm-like chain polymer, using Monte Carlo methods, and assessed the corresponding rupture force spectra. It was found th...
Relativistic Linear Restoring Force
Clark, D.; Franklin, J.; Mann, N.
2012-01-01
We consider two different forms for a relativistic version of a linear restoring force. The pair comes from taking Hooke's law to be the force appearing on the right-hand side of the relativistic expressions: d"p"/d"t" or d"p"/d["tau"]. Either formulation recovers Hooke's law in the non-relativistic limit. In addition to these two forces, we…
Theory of intermolecular forces
Margenau, H; Ter Haar, D
1971-01-01
Theory of Intermolecular Forces deals with the exposition of the principles and techniques of the theory of intermolecular forces. The text focuses on the basic theory and surveys other aspects, with particular attention to relevant experiments. The initial chapters introduce the reader to the history of intermolecular forces. Succeeding chapters present topics on short, intermediate, and long range atomic interactions; properties of Coulomb interactions; shape-dependent forces between molecules; and physical adsorption. The book will be of good use to experts and students of quantum mechanics
Intermolecular and surface forces
Israelachvili, Jacob N
2011-01-01
This reference describes the role of various intermolecular and interparticle forces in determining the properties of simple systems such as gases, liquids and solids, with a special focus on more complex colloidal, polymeric and biological systems. The book provides a thorough foundation in theories and concepts of intermolecular forces, allowing researchers and students to recognize which forces are important in any particular system, as well as how to control these forces. This third edition is expanded into three sections and contains five new chapters over the previous edition.· starts fr
Maggs, William Ward
Hopes that geophysicists might be able to document a fifth force of nature have diminished, as new measurements and analyses of earlier geodetic experiments have yielded no solid evidence of a non-Newtonian component of gravity.Modern physics recognizes four fundamental forces with distinct spheres of influence: The strong and weak nuclear forces operate over the range of one atom, while gravity and electromagnetism have an infinite range. Gravity measurements over a few centimeters in laboratories and over millions of kilometers in space continue to buttress Issac Newton's conclusion that the gravitational force between two objects decreases as the square of the distance between them.
Climate forcings and feedbacks
Hansen, James
1993-01-01
Global temperature has increased significantly during the past century. Understanding the causes of observed global temperature change is impossible in the absence of adequate monitoring of changes in global climate forcings and radiative feedbacks. Climate forcings are changes imposed on the planet's energy balance, such as change of incoming sunlight or a human-induced change of surface properties due to deforestation. Radiative feedbacks are radiative changes induced by climate change, such as alteration of cloud properties or the extent of sea ice. Monitoring of global climate forcings and feedbacks, if sufficiently precise and long-term, can provide a very strong constraint on interpretation of observed temperature change. Such monitoring is essential to eliminate uncertainties about the relative importance of various climate change mechanisms including tropospheric sulfate aerosols from burning of coal and oil smoke from slash and burn agriculture, changes of solar irradiance changes of several greenhouse gases, and many other mechanisms. The considerable variability of observed temperature, together with evidence that a substantial portion of this variability is unforced indicates that observations of climate forcings and feedbacks must be continued for decades. Since the climate system responds to the time integral of the forcing, a further requirement is that the observations be carried out continuously. However, precise observations of forcings and feedbacks will also be able to provide valuable conclusions on shorter time scales. For example, knowledge of the climate forcing by increasing CFC's relative to the forcing by changing ozone is important to policymakers, as is information on the forcing by CO2 relative to the forcing by sulfate aerosols. It will also be possible to obtain valuable tests of climate models on short time scales, if there is precise monitoring of all forcings and feedbacks during and after events such as a large volcanic eruption
On the decomposition of forces
Directory of Open Access Journals (Sweden)
Dong Eui Chang
2014-01-01
Full Text Available We show that any continuously differentiable force is decomposed into the sum of a Rayleigh force and a gyroscopic force. We also extend this result to piecewise continuously differentiable forces. Our result improves the result on the decomposition of forces in a book by David Merkin and further extends it to piecewise continuously differentiable forces.
Elementary Particles and Forces.
Quigg, Chris
1985-01-01
Discusses subatomic particles (quarks, leptons, and others) revealed by higher accelerator energies. A connection between forces at this subatomic level has been established, and prospects are good for a description of forces that encompass binding atomic nuclei. Colors, fundamental interactions, screening, camouflage, electroweak symmetry, and…
Hestenes, David; And Others
1992-01-01
Reports the rationale, design, validation, and uses of the "Force Concept Inventory," an instrument to assess the students' beliefs on force. Includes results and implications of two studies that compared the inventory with the "Mechanics Baseline." Includes a copy of the instrument. (MDH)
Antila, Hanne S; Salonen, Emppu
2013-01-01
This chapter provides an overview of the most common methods for including an explicit description of electronic polarization in molecular mechanics force fields: the induced point dipole, shell, and fluctuating charge models. The importance of including polarization effects in biomolecular simulations is discussed, and some of the most important achievements in the development of polarizable biomolecular force fields to date are highlighted.
El-Kirat-Chatel, Sofiane; Beaussart, Audrey; Vincent, Stéphane P.; Abellán Flos, Marta; Hols, Pascal; Lipke, Peter N.; Dufrêne, Yves F.
2015-01-01
In the baker's yeast Saccharomyces cerevisiae, cell-cell adhesion (``flocculation'') is conferred by a family of lectin-like proteins known as the flocculin (Flo) proteins. Knowledge of the adhesive and mechanical properties of flocculins is important for understanding the mechanisms of yeast adhesion, and may help controlling yeast behaviour in biotechnology. We use single-molecule and single-cell atomic force microscopy (AFM) to explore the nanoscale forces engaged in yeast flocculation, focusing on the role of Flo1 as a prototype of flocculins. Using AFM tips labelled with mannose, we detect single flocculins on Flo1-expressing cells, showing they are widely exposed on the cell surface. When subjected to force, individual Flo1 proteins display two distinct force responses, i.e. weak lectin binding forces and strong unfolding forces reflecting the force-induced extension of hydrophobic tandem repeats. We demonstrate that cell-cell adhesion bonds also involve multiple weak lectin interactions together with strong unfolding forces, both associated with Flo1 molecules. Single-molecule and single-cell data correlate with microscale cell adhesion behaviour, suggesting strongly that Flo1 mechanics is critical for yeast flocculation. These results favour a model in which not only weak lectin-sugar interactions are involved in yeast flocculation but also strong hydrophobic interactions resulting from protein unfolding.
DEFF Research Database (Denmark)
Bialynicki-Birula, I; Cirone, M.A.; Dahl, Jens Peder;
2002-01-01
We present Heisenberg's equation of motion for the radial variable of a free non-relativistic particle in D dimensions. The resulting radial force consists of three contributions: (i) the quantum fictitious force which is either attractive or repulsive depending on the number of dimensions, (ii) ...
DEFF Research Database (Denmark)
Maffiuletti, Nicola A; Aagaard, Per; Blazevich, Anthony J;
2016-01-01
The evaluation of rate of force development during rapid contractions has recently become quite popular for characterising explosive strength of athletes, elderly individuals and patients. The main aims of this narrative review are to describe the neuromuscular determinants of rate of force...
Energy Technology Data Exchange (ETDEWEB)
Bell, R.E.; Hartley, D.S.III; Packard, S.L.
1999-05-01
This report documents refined requirements for tools to aid the process of force design in Operations Other Than War (OOTWs). It recommends actions for the creation of one tool and work on other tools relating to mission planning. It also identifies the governmental agencies and commands with interests in each tool, from whom should come the user advisory groups overseeing the respective tool development activities. The understanding of OOTWs and their analytical support requirements has matured to the point where action can be taken in three areas: force design, collaborative analysis, and impact analysis. While the nature of the action and the length of time before complete results can be expected depends on the area, in each case the action should begin immediately. Force design for OOTWs is not a technically difficult process. Like force design for combat operations, it is a process of matching the capabilities of forces against the specified and implied tasks of the operation, considering the constraints of logistics, transport and force availabilities. However, there is a critical difference that restricts the usefulness of combat force design tools for OOTWs: the combat tools are built to infer non-combat capability requirements from combat capability requirements and cannot reverse the direction of the inference, as is required for OOTWs. Recently, OOTWs have played a larger role in force assessment, system effectiveness and tradeoff analysis, and concept and doctrine development and analysis. In the first Quadrennial Defense Review (QDR), each of the Services created its own OOTW force design tool. Unfortunately, the tools address different parts of the problem and do not coordinate the use of competing capabilities. These tools satisfied the immediate requirements of the QDR, but do not provide a long-term cost-effective solution.
A functional approach to quantum friction: effective action and dissipative force
Farías, M Belén; Lombardo, Fernando C; Mazzitelli, Francisco D; López, Adrián E Rubio
2014-01-01
We study the Casimir friction due to the relative, uniform, lateral motion of two parallel mirrors coupled to a vacuum real scalar field, $\\phi$. We follow a functional approach, whereby nonlocal terms in the action for $\\phi$, concentrated on the mirrors' locii, appear after functional integration of the microscopic degrees of freedom. This action for $\\phi$, which incorporates the relevant properties of the mirrors, is then used as the starting point for two complementary evaluations: Firstly, we calculate the { in-out} effective action for the system, which develops an imaginary part, hence a non-vanishing probability for the decay (because of friction) of the initial vacuum state. Secondly, we evaluate another observable: the vacuum expectation value of the frictional force, using the { in-in} or Closed Time Path formalism. Explicit results are presented for zero-width mirrors and half-spaces, in a model where the microscopic degrees of freedom at the mirrors are a set of identical quantum harmonic oscill...
DEFF Research Database (Denmark)
Lindemann, J.; Damkilde, Lars
2009-01-01
ForcePAD is a 2-dimensional finite element application that started as a concept application for finite element modeling. Over the course of 10 years the application has been evolved into an application that is used extensively in both an educational setting as well as a tool for design and engin...... engineering. In the latest version of ForcePAD an optimization module was added to enable to take advantage of topology optimization in the design process....
Energy Technology Data Exchange (ETDEWEB)
Bing, G.; Chrzanowski, P.; May, M.; Nordyke, M.
1989-04-06
The Strategic Forces Briefing'' is our attempt, accomplished over the past several months, to outline and highlight the more significant strategic force issues that must be addressed in the near future. Some issues are recurrent: the need for an effective modernized Triad and a constant concern for force survivability. Some issues derive from arms control: the Strategic Arms Reduction Talks (SALT) are sufficiently advanced to set broad numerical limits on forces, but not so constraining as to preclude choices among weapon systems and deployment modes. Finally, a new administration faced with serious budgetary problems must strive for the most effective strategic forces limited dollars can buy and support. A review of strategic forces logically begins with consideration of the missions the forces are charged with. We begin the briefing with a short review of targeting policy and implementation within the constraints of available unclassified information. We then review each element of the Triad with sections on SLBMs, ICBMs, and Air-Breathing (bomber and cruise missile) systems. A short section at the end deals with the potential impact of strategic defense on offensive force planning. We consider ABM, ASAT, and air defense; but we do not attempt to address the technical issues of strategic defense per se. The final section gives a brief overview of the tritium supply problem. We conclude with a summary of recommendations that emerge from our review. The results of calculation on the effectiveness of various weapon systems as a function of cost that are presented in the briefing are by Paul Chrzanowski.
DEFF Research Database (Denmark)
Pedersen, Preben Terndrup
1996-01-01
The purpose of these notes is to present a basis for the estimation of the internal collision forces between conventinal merchant vessels and large volume offshore structures in the form of gravity-supported offshore installations and bridges crossing international shipping routes.The main emphas...... is on the presentation of impact loads on fixed offshore structures due to bow collisions. The crushing forces are determined as functions of vessels size, vessels speed, bow profile, collision angles and eccentric impacts....
Roland Bennewitz
2005-01-01
Friction force microscopy (FFM) can detect lateral force variations on the atomic scale when sliding a sharp tip over a flat surface. The sliding often takes the form of a stick-slip movement with the same periodicity as the atomic lattice. Here, I discuss how the occurrence of stick-slip instabilities is related to the onset of dissipation. The velocity and load dependence of atomic friction on various materials are discussed in the light of simple classical laws of friction.
Forced ventilation increases variability of isometric finger forces
Li, Sheng; Yasuda, Nobuo
2006-01-01
The study aimed to assess the effects of forced ventilation on variability of the index finger force at the submaximal levels. Fourteen (6 men, 8 women) healthy subjects were instructed to perform self-initiated forced inspiration and forced expiration, the Valsalva maneuver and normal breathing while sustaining 15%, 30%, and 45% of maximal voluntary contraction (MVC) by the index finger. Standard deviation (S.D.) of finger forces increased significantly with the level of force. At each level...
Radiative forcing by contrails
Energy Technology Data Exchange (ETDEWEB)
Meerkoetter, R.; Schumann, U. [DLR Oberpfaffenhofen, Wessling (Germany). Inst. fuer Phys. der Atmosphaere; Doelling, D.R.; Minnis, P. [National Aeronautics and Space Administration, Hampton, VA (United States). Langley Research Center; Nakajima, T.; Tsushima, Y. [Tokyo Univ. (Japan). Center for Climate System Research
1999-08-01
A parametric study of the instantaneous radiative impact of contrails is presented using three different radiative transfer models for a series of model atmospheres and cloud parameters. Contrails are treated as geometrically and optically thin plane parallel homogeneous cirrus layers in a static atmosphere. The ice water content is varied as a function of ambient temperature. The model atmospheres include tropical, midlatitude, and subarctic summer and winter atmospheres. Optically thin contrails cause a positive net forcing at top of the atmosphere. At the surface the radiative forcing is negative during daytime. The forcing increases with the optical depth and the amount of contrail cover. At the top of the atmosphere, a mean contrail cover of 0.1% with average optical depth of 0.2 to 0.5 causes about 0.01 to 0.03 Wm{sup -2} daily mean instantaneous radiative forcing. Contrails cool the surface during the day and heat the surface during the night, and hence reduce the daily temperature amplitude. The net effect depends strongly on the daily variation of contrail cloud cover. The indirect radiative forcing due to particle changes in natural cirrus clouds may be of the same magnitude as the direct one due to additional cover. (orig.) 78 refs.
Radiative forcing by contrails
Directory of Open Access Journals (Sweden)
R. Meerkötter
Full Text Available A parametric study of the instantaneous radiative impact of contrails is presented using three different radiative transfer models for a series of model atmospheres and cloud parameters. Contrails are treated as geometrically and optically thin plane parallel homogeneous cirrus layers in a static atmosphere. The ice water content is varied as a function of ambient temperature. The model atmospheres include tropical, mid-latitude, and subarctic summer and winter atmospheres. Optically thin contrails cause a positive net forcing at top of the atmosphere. At the surface the radiative forcing is negative during daytime. The forcing increases with the optical depth and the amount of contrail cover. At the top of the atmosphere, a mean contrail cover of 0.1% with average optical depth of 0.2 to 0.5 causes about 0.01 to 0.03 Wm^{-2} daily mean instantaneous radiative forcing. Contrails cool the surface during the day and heat the surface during the night, and hence reduce the daily temperature amplitude. The net effect depends strongly on the daily variation of contrail cloud cover. The indirect radiative forcing due to particle changes in natural cirrus clouds may be of the same magnitude as the direct one due to additional cover.
Key words. Atmospheric composition and structure (aerosols and particles · Meteorology and atmospheric dynamics (climatology · radiative processes