Global consequences of a local Casimir force: Adhered cantilever

Although stiction is a cumbersome problem for microsystems, it stimulates investigations of surface adhesion. In fact, the shape of an adhered cantilever carries information of the adhesion energy that locks one end to the substrate. We demonstrate here that the system is also sensitive to the dispersion forces that are operative very close to the point of contact, but their contribution to the shape is maximum at about one third of the unadhered length. When the force exceeds a critical value the cantilever does not lose stability but it settles at smaller unadhered length, whose relation to adhesion energy is only slightly affected by the force. Our calculations suggest to use adhered cantilevers to measure the dispersion forces at short separations, where other methods suffer from jump-to-contact instability. Simultaneous measurement of the force and adhesion energy allows the separation of the dispersion contribution to the surface adhesion.Comment: 5 pages, 3 figure

Thermal Casimir-Polder interaction of different atoms with graphene

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 conclude that the theoretical predictions following from the two models can be reliably discriminated in experiments on quantum reflection of different atoms on graphene.Comment: 19 pages, 6 figures, to appear in Phys. Rev.

Comparison of the hydrodynamic and Dirac models of the dispersion interaction between graphene and H, He∗{}^{\ast}, or Na atoms

The van der Waals and Casimir-Polder interaction of different atoms with graphene is investigated using the Dirac model which assumes that the energy of quasiparticles is linear with respect to the momentum. The obtained results for the van der Waals coefficients of hydrogen atoms and molecules and atoms of metastable He${}^{\ast}$ and Na as a function of separation are compared with respective results found using the hydrodynamic model of graphene. It is shown that, regardless of the value of the gap parameter, the Dirac model leads to much smaller values of the van der Waals coefficients than the hydrodynamic model. The experiment on quantum reflection of metastable He${}^{\ast}$ and Na atoms on graphene is proposed which is capable to discriminate between the two models of the electronic structure of graphene. In this respect the parameters of the phenomenological potential for both these atoms interacting with graphene described by different models are determined.Comment: 15 pages, 4 figure

Efficient calculation of van der Waals dispersion coefficients with time-dependent density functional theory in real time: application to polycyclic aromatic hydrocarbons

The van der Waals dispersion coefficients of a set of polycyclic aromatic hydrocarbons, ranging in size from the single-cycle benzene to circumovalene (C66H20), are calculated with a real-time propagation approach to time-dependent density functional theory (TDDFT). In the non-retarded regime, the Casimir-Polder integral is employed to obtain C6, once the dynamic polarizabilities have been computed at imaginary frequencies with TDDFT. On the other hand, the numerical coefficient that characterizes the fully retarded regime is obtained from the static polarizabilities. This ab initio strategy has favorable scaling with the size of the system - as demonstrated by the size of the reported molecules - and can be easily extended to obtain higher order van der Waals coefficients.Comment: submitted to J. Chem. Phy

Substrate Inhibition Growth Kinetics for Cutinase Producing Pseudomonas cepacia Using Tomato-peel Extracted Cutin

Using tomato-peel extracted cutin, an economically viable substrate, cutinase production by Pseudomonas cepacia was studied at different initial substrate concentrations (2–20 g L–1). The highest volumetric enzyme activity was observed at 10 g L–1 of cutin, which was inhibited at further higher concentrations. Various 3-, 4- and 5- parametric Monod-variant models were chosen to analyze the inhibition kinetics. The model parameters as well as goodness of fit were estimated using non-linear regression analysis. The 4- parameter Webb model was the best-fit model (R2 = 0.933), followed by the 3-parameter Andrews model (R2 = 0.92). Parameter sensitivity analysis revealed that the maximum specific growth rate was the most sensitive parameter for both the models, and the Webb constant was the least sensitive. Finally, based on a strong evidence ratio 190.65 from Akaike’s information content criteria analysis as well as extra sum of square F test (P > 0.05), it was found that 3-parameter Andrews model gave the best fit

Precision measurement of the Casimir-Lifshitz force in a fluid

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 consistent with Lifshitz's theory.Comment: 6 pages, 3 figures. (version before final publication

Design of Pulse Generator in 180nm Technology for GPR Applications

In this work, we present a low-complexity and low cost pulse generator in 180nm technology for ground penetrating ultra-wideband (UWB) radar system applications. Here I have implemented an UWB pulse generator circuit. A UWB pulse generator is a method introduced in communication system to simplify the data transmission and remove disadvantages that occurs in other systems. This generator generates a Gaussian pulse for a small period of time of the order of some nanoseconds. As UWB pulses are generated for a short time, hence no carrier signal is required to send a base band or message signal. So power loss due to carrier signal doesn’t exist at all. These pulses are very high in frequency; hence it has very less chance to be got affected by noise. This pulse generator uses a delay generator along with a Gilbert XOR cell for generating a Gaussian pulse which can be shaped by using a FIR filter, and finally a Gaussian mono cycle pulse is observed at the output which has a pulse width of 97ps thereby give rise to a bandwidth of 10.3 GHz which meet the FCC requirements. The pulse generator comprises of three cascaded delay blocks, a XOR block, and a FIR filter. The interpolation delay blocks uses voltage for adjusting the delay time by the control of the gains of each path. By adjusting the delay time, pulse generator can achieve the required frequency. The XOR gate is implemented using a Gilbert cell. When the two signals given as input have opposite voltage levels at a given time, the XOR gate creates a pulse. After the XOR gate, a Gaussian pulse is generated and then it goes through the FIR filter to shape it to a Gaussian mono cycle pulse. The design and simulation of the pulse generator was performed using the Cadence UMC tool in 180nm CMOS process

Dependences of the Casimir-Polder interaction between an atom and a cavity wall on atomic and material properties

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.Comment: 5 pages, 1 figure, iopart.cls is used, to appear in J. Phys. A (special issue: Proceedings of QFEXT05, Barcelona, Sept. 5-9, 2005

Enhanced dispersion interaction in confined geometry

The dispersion interaction between two point-like particles confined in a dielectric slab between two plates of another dielectric medium is studied within a continuum (Lifshitz) theory. The retarded (Casimir-Polder) interaction at large inter-particle distances is found to be strongly enhanced as the mismatch between the dielectric permittivities of the two media is increased. The large-distance interaction is multiplied due to confinement by a factor of $(33\gamma^{5/2}+13\gamma^{-3/2})/46$ at zero temperature, and by $(5\gamma^2+\gamma^{-2})/6$ at finite temperature, \gamma=\ein(0)/\eout(0) being the ratio between the static dielectric permittivities of the inner and outer media. This confinement-induced amplification of the dispersion interaction can reach several orders of magnitude.Comment: 4 page

Stable suspension and dispersion-induced transitions from repulsive Casimir forces between fluid-separated eccentric cylinders

Using an exact numerical method for finite 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, via a method to compute Casimir torques for finite objects. Furthermore, the stable orientation of the square cylinder is shown to undergo an unusual 45 degrees transition as a function of the separation lengthscale, which is explained as a consequence of material dispersion.Comment: Published in Physical Review Letters. Vol. 101, page, 190404 (2008