Halving the Casimir force with conductive oxides

The possibility to modify the strength of the Casimir effect by tailoring the dielectric functions of the interacting surfaces is regarded as a unique opportunity in the development of Micro- and NanoElectroMechanical Systems. In air, however, one expects that, unless noble metals are used, the electrostatic force arising from trapped charges overcomes the Casimir attraction, leaving no room for exploitation of Casimir force engineering at ambient conditions. Here we show that, in the presence of a conductive oxide, the Casimir force can be the dominant interaction even in air, and that the use of conductive oxides allows one to reduce the Casimir force up to a factor of 2 when compared to noble metals.Comment: modified version, accepted for publication in Phys Rev Let

No anomalous scaling in electrostatic calibrations for Casimir force measurements

In a recent paper (Phys.Rev.A78, 020101(R) (2008)), Kim at al. have reported a large anomaly in the scaling law of the electrostatic interaction between a sphere and a plate, which was observed during the calibration of their Casimir force set-up. Here we experimentally demonstrate that in proper electrostatic calibrations the scaling law follows the behavior expected from elementary electrostatic arguments, even when the electrostatic voltage that one must apply to minimize the force (typically ascribed to contact potentials) depends on the separation between the surfaces.Comment: Final versio

Fiber-top atomic force microscope

We present the implementation of an atomic force microscope (AFM) based on fiber-top design. Our results demonstrate that the performances of fiber-top AFMs in contact mode are comparable to those of similar commercially available instruments. Our device thus represents an interesting\ud alternative to existing AFMs, particularly for applications outside specialized research laboratories, where a compact, user-friendly, and versatile tool might often be preferred

High-Q nested resonator in an actively stabilized optomechanical cavity

Experiments involving micro- and nanomechanical resonators need to be carefully designed to reduce mechanical environmental noise. A small scale on-chip approach is to add an additional resonator to the system as a mechanical low-pass filter. Unfortunately, the inherent low frequency of the low-pass filter causes the system to be easily excited mechanically. Fixating the additional resonator ensures that the resonator itself can not be excited by the environment. This, however, negates the purpose of the low-pass filter. We solve this apparent paradox by applying active feedback to the resonator, thereby minimizing the motion with respect the front mirror of an optomechanical cavity. Not only does this method actively stabilize the cavity length, but it also retains the on-chip vibration isolation.Comment: Minor adjustments mad

Orbitabodemfracturen

De orbitabodem kan betrokken raken bij diverse fracturen van het aangezichtsskelet. Bij een zygomafractuur, een bovenkaakfractuur van het type Le Fort IJ en een orbitabodem-randfractuur loopt de fractuurlijn steeds door de orbitabodem. De bodemfractuur is in deze gevallen een onderdeel van een meer uitgebreide middengezichtsfractuur. Bij een bovenkaakfractuur van het typeLeFort II zijn bovendien beide orbitabodems gefractureerd. Naast deze zogenaamde gecombineerde orbitabodemfracturen komt de bodemfractuur in geïsoleerde vorm voor, in navolging van Converse en Smith (1957) meestal "blow-out" fractuur genoemd. Gedurende de laatste 25 jaar zijn de klinische en röntgenologische aspecten, alsmede de indicaties tot en de methodes van operatieve behandeling van orbitabodemfracturen uitvoerig beschreven in de ophthalmologische, otolaryngologische, plastische, kaakchirurgische en radiologische literatuur. Hoewel enkele beginselen van diagnostiek en behandeling tegenwoordig algemeen worden aanvaard, is er nog altijd geen consensus over beide. Van grote betekenis voor de wijze van diagnostiek en behandeling van orbitabodemfracturen zijn de in dit verband inmiddels beroemd geworden publicaties van Converse en Smith (1957) en Smith en Regan (1957) geweest. De auteurs vestigen hierin de aandacht op de mogelijkheid van zich langzaam ontwikkelende diplopie en enophthalmus bij niet of slecht behandelde blow-out fracturen en adviseren daarom vroegtijdige exploratie en reconstructie van de orbitabodem en het aanbrengen van een bodemimplantaat. In de daarop volgende jaren ontstond bij steeds meer operateurs de mening dat een blow-out fractuur een frequent vóórkomende fractuur is (Anderson en Teague 1963, Smith 1963, Reehen Tsujimura 1966, Greenwald e.a. 1974), die dikwijls over het hoofd wordt gezien (Converse en Smith 1960, Müsebeck 1966, Borghouts en Otto 1974). De kans op late* diplopie en enophthalmus zou bovendien niet alleen bestaan bij blow-out fracturen, maar ook bij gecombineerde orbitabodemfracturen (Freeman 1962, McCoy e.a. 1962, Dodd en Abrahams 1963, Cramer e.a. 1965, Davies 1972, Crewe 1978). Sommige auteurs (Bleeker en Van Ommen 1959, Cramer e.a. 1965, Hötte 1970, Diamant 1980) neigen er zelfs toe de diagnostische criteria van een blow-out fractuur uit te breiden en ook niet-geïsoleerde bodemfracturen blow-out, impure blow-out of orbitafractuur te noemen

Using Networks For Changing Innovation Strategy: The Case of IBM

Large-scale strategic change projects in companies may be supported by using alliance networks. This paper shows that IBM’s change from an exploitation strategy towards an exploration strategy required a radically different network strategy as well. By entering into more non-equity alliances, involving new partners in the network and loosening the ties with existing partners, IBM supported its transformation from a hardware manufacturing company to a global service provider and software company

Influence of preload and nonlinearity of railpads on vibration of railway tracks under stationary and moving harmonic loads

In railway track dynamics, the stiffness and damping properties of railpads have a significant effect on track vibration, decay rates as well forces transmitted to the track supporting structure. Many studies have shown that railpads exhibit pronounced nonlinear behaviour, with preload and frequency dependent properties. This paper presents a three parameter railpad model, together with its differential equation of motion and the required model parameters obtained from experimental data. A time domain model of a rail discretely supported on these railpads is then formulated using the finite element method. The model is subjected to static and dynamic loading in order to study the effects of preload and frequency on its dynamic behaviour. Results are shown as time histories and frequency spectra for the track displacements and reaction forces for various preload levels. They emphasise the necessity of accounting for nonlinear behaviour based on the large disparities (up to 20 dB) observed between the linear and nonlinear cases for the parameters used in this study