Tunable mechanical resonator with aluminum nitride piezoelectric

The electromechanical response of piezoelectrically-actuated AlN micromachined bridge resonators has been characterized using laser interferometry and electrical admittance measurements. We compare the response of microbridges with different dimensions and buckling (induced by the initial residual stress of the layers). The resonance frequencies are in good agreement with numerical simulations of the electromechanical behavior of the structures. We show that it is possible to perform a rough tuning of the resonance frequencies by allowing a determined amount of builtin stress in the microbridge during its fabrication. Once the resonator is made, a DC bias added to the AC excitation signal allows to fine-tune the frequency. Our microbridges yield a tuning factor of around 88 Hz/V for a 500 ?m-long microbridge.

Dual-Band Tunable Recursive Active Filter

This letter presents a novel recursive active filter topology that provides dual-band performance, with independent tuning capability in both bands. The dual-band operation is achieved by using two independent feedback lines. Additionally, linear phase shifters based on left-handed cells are included in these two branches in order to tune the center frequency of both pass bands.

Synchrotron X-ray photoabsorption spectroscopy of plasmas

Theoretical X-ray opacities are used in numerous radiative transfer simulations of plasmas at different temperatures and densities, for example astrophysics, fusion, metrology and EUV and X-rays radiation sources. However, there are only a reduced number of laboratories working on the validation of those theoretical results empirically, in particular for high temperature plasmas (mayor que 1eV). One of those limitations comes from the use of broad band EUV- X ray sources to illuminate the plasma which, among other issues, present low reproducibility and repetition rate [1]. Synchrotron radiation facilities are a more appropriate radiation source in that sense, since they provide tunable, reproducible and high resolution photons. Only their ?low? photon intensity for these experiments has prevented researchers to use it for this purpose. However, as new synchrotron facilities improve their photon fluxes, this limitation not longer holds [2]. This work evaluates the experimental requirements to use third generation synchrotron radiation sources for the empirical measurement of opacities of plasmas, proposing a pausible experimental set-up to carry them out. Properties of the laser or discharge generated plasmas to be studied with synchrotron radiation will be discussed in terms of their maximum temperatures, densities and temporal evolution. It will be concluded that there are encouraging reasons to pursue these kind of experiments which will provide with an appropriate benchmark for theoretical opacities

Electrooptic characterization of tunable cylindrical liquid crystal lenses

In this work, one-dimensional arrays of cylindrical adaptive liquid crystal lenses were manufactured and characterized; and test devices were filled with nematic liquid crystal. Comb interdigitated electrodes were designed as a mask pattern for the control electrode on the top glass substrates. A radial graded refractive index along each microsized lens was achieved by fabricating a layer of high resistance sheet deposited as a control electrode. These tunable lenses were switched by applying amplitude and frequency optimized waveforms on the control electrode. Phase profiles generated by the radial electric field distribution on each lens were measured by a convectional interferometric technique.

2D tunable graded index prism beam steering device based on nematic liquid crystals

Liquid crystal devices are being used in many non-display applications in order to construct small devices controlled by low voltage electronics without mechanical components. In this work, we present a novel liquid crystal device for laser beam steering. In this device the orientation of the liquid crystal molecules can be controlled. A change in the liquid crystal orientation results in a change of the refractive index. When a laser beam passes through the device, the beam will be deviated (Fig.1) and the device works a prism. The main difference between this device and a prism is that in the device the orientation profile of the liquid crystal molecules can be modified so that the laser beam can be deviated a required angle: the device is tuneable.

Electrically tunable delay for trains of optical pulses

A technique to implement an electrically tunable delay line with high bandwidth for trains of ultrashort optical pulses is presented. The system is based on the temporal self-imaging effect in fiber gratings and electrooptic modulation.

Tunable Fano resonance in symmetric multilayered gold nanoshells

Fano resonances (FRs) are produced when a discrete state is coupled with a continuum. In addition to fundamental scientific interests, FRs in plasmonic systems give rise to the so-called plasmon-induced transparency. In this work we have studied the evolution of dipole-dipole all-plasmonic FRs in symmetric multilayered nanoshells as the function of their geometrical parameters. We demonstrate that symmetry breaking is not mandatory for controlling the Fano resonance in such multilayered nanoshells. Generation of FRs in these symmetric nanostructures presents clear advantages over their asymmetric counterparts, as they are easier to fabricate and can be used in a wider range of technological applications.

Tunable Fano resonance in symmetric multilayered gold nanoshells

We have studied the evolution of dipole–dipole all-plasmonic Fano resonances (FRs) in symmetric multilayered nanoshells as a function of their geometrical parameters. We demonstrate that symmetry breaking is not mandatory for controlling the Fano resonance in such multilayer structures. By carefully selecting the geometrical parameters, the position of the FR can be tuned between 600 and 950 nm and its intensity can be increased up to four fold with respect to the non-optimized structures. Generation of FRs in such symmetric nanostructures presents clear advantages over their asymmetric counterparts, as they are easier to fabricate and can be used in a wider range of technological applications.

Wedged analog tunable beam steering device based on cholesteric liquid crystals

In this work we propose a novel cholesteric liquid crystal beam steering device based on the Kerr effect. The first version of the device consists of two ITO coated glass plates, with intentionally prepared electrodes, assembled together with a thickness gradient between both sides of the device. One side of the cell has two substrates at direct contact; the other side has separated substrates to form the wedge. The cell was filled with a cholesteric liquid crystal. The liquid crystal material is an innovative mixture called 1892E with extremely low viscosity doped with a ZLI chiral nematogen. The proposed beam steering device based on cholesteric liquid crystals has great potential for many photonic applications. Results describing the performance of the device and the properties of the selected liquid crystals are presented.

Tunable liquid crystal-photonic crystal fiber interferometer

In this work, we present a novel interferometer based on liquid crystal and photonic crystal fiber technology. The objective of this project is the development of a tunable (switchable) modal (Mach-Zehnder) interferometer for optical communications or sensing.

Thermally tunable polarization by nanoparticle plasmonic resonance in photonic crystal fibers

A photonic crystal fiber selectively filled with silver nanoparticles dispersed in polydimethylsiloxane has been numerically studied via finite elements analysis. These nanoparticles possess a localized surface plasmon resonance in the visible region which depends on the refractive index of the surrounding medium. The refractive index of polydimethylsiloxane can be thermally tuned leading to the design of polarization tunable filters. Filters found with this setup show anisotropic attenuation of the x-polarization fundamental mode around ?x = 1200dB/cm remarkably higher than the y-polarization mode. Moreover, high fiber birefringence and birefringence reversal is observed in the spectral region of the plasmon.

Aldol sensors for the rapid generation of tunable fluorescence by antibody catalysis

The synthesis of novel fluorogenic retro-aldol substrates for aldolase antibody 38C2 is described. These substrates are efficiently and specifically processed by antibody aldolases but not by natural cellular enzymes. Together, the fluorogenic substrates and antibody aldolases provide reporter gene systems that are compatible with living cells. The broad scope of the antibody aldolase allows for the processing of a range of substrates that can be designed to allow fluorescence monitoring at a variety of wavelengths. We also have developed the following concept in fluorescent protein tags. β-Diketones bearing a fluorescent tag are bound covalently by the aldolase antibody and not other proteins. We anticipate that proteins fused with the antibody can be tagged specifically and covalently within living cells with fluorophores of virtually any color, thereby providing an alternative to green fluorescent protein fusions.

Deliberate self harm: systematic review of efficacy of psychosocial and pharmacological treatments in preventing repetition

Objective: To identify and synthesise the findings from all randomised controlled trials that have examined the effectiveness of treatments of patients who have deliberately harmed themselves.

The repetition of large-earthquake ruptures.

This survey of well-documented repeated fault rupture confirms that some faults have exhibited a "characteristic" behavior during repeated large earthquakes--that is, the magnitude, distribution, and style of slip on the fault has repeated during two or more consecutive events. In two cases faults exhibit slip functions that vary little from earthquake to earthquake. In one other well-documented case, however, fault lengths contrast markedly for two consecutive ruptures, but the amount of offset at individual sites was similar. Adjacent individual patches, 10 km or more in length, failed singly during one event and in tandem during the other. More complex cases of repetition may also represent the failure of several distinct patches. The faults of the 1992 Landers earthquake provide an instructive example of such complexity. Together, these examples suggest that large earthquakes commonly result from the failure of one or more patches, each characterized by a slip function that is roughly invariant through consecutive earthquake cycles. The persistence of these slip-patches through two or more large earthquakes indicates that some quasi-invariant physical property controls the pattern and magnitude of slip. These data seem incompatible with theoretical models that produce slip distributions that are highly variable in consecutive large events.