Mass sensing using an amorphous silicon MEMS resonator

Bilayer micro-bridge resonators of amorphous silicon and titanium were fabricated on a glass substrate at 100°C by surface micromachining using an aluminum sacrificial layer. Au square patterns with sub-micrometer dimensions were patterned on top of the microresonators. These Au squares allowed specific immobilization of thiolated single strand DNA probe oligonucleotides. The frequency response of the electrostatically-actuated resonators was measured optically. The mass loading effect of the Au squares and of the immobilized ssDNA probes were determined by the shift in the resonance frequency of the micro-bridge resonators

Hydrogenated Amorphous Silicon Thin-Film Disk Resonators

AbstractMicroelectromechanical (MEMS) structures consisting of surface micromachined disk resonators of phosphorous- doped hydrogenated amorphous silicon (n-a-Si:H) deposited by radiofrequency plasma enhanced chemical vapour deposition (RF-PECVD) were fabricated and characterized. Quality factors up to 104 in vacuum were measured for disk resonators operating at frequencies between 0.1 and 10MHz. The metallized structures were actuated with electrostatic force by radially placed electrodes. Finite element simulations were used to identify the type of vibrational modes present and show good agreement with measured values. Resonator geometry and ambient pressure were varied to attain a generalized understanding of the RF performance. Higher harmonic modes show increasing quality factors which bears great potential when designing sensors for operation in dissipative media

UV-divergences of Wilson Loops for Gauge/Gravity Duality

We analyze the structure of the UV divergences of the Wilson loop for a general gauge/gravity duality. We find that, due to the presence of a nontrivial NSNS B-field and metric, new divergences that cannot be subtracted out by the conventional Legendre transform may arise. We also derive conditions on the B-field and the metric, which when satisfied, the leading UV divergence will become linear, and can be cancelled out by choosing the boundary condition of the string appropriately. Our results, together with the recent result of arXiv:0807.5127, where the effect of a nontrivial dilaton on the structure of UV divergences in Wilson loop is analysed, allow us to conclude that Legendre transform is at best capable of cancelling the linear UV divergences arising from the area of the worldsheet, but is incapable to handle the divergences associated with the dilaton or the B-field in general. We also solve the conditions for the cancellation of the leading linear divergences generally and find that many well-known supergravity backgrounds are of these kinds, including examples such as the Sakai-Sugimoto QCD model or N=1 duality with Sasaki-Einstein spaces. We also point out that Wilson loop in the Klebanov-Strassler background have a divergence associated with the B-field which cannot be cancelled away with the Legendre transform. Finally we end with some comments on the form of the Wilson loop operator in the ABJM superconformal Chern-Simons theory.Comment: 26 pages. LaTeX. v2: reference added. version to appear in JHE

Microelectromechanical resonators based on an all polymer/carbon nanotube composite structural material

Carboxylated multi-wall carbon-nanotubes (CNTs) monolayers are integrated on microfabricated all-polymer micro-electromechanical systems (pMEMS) resonator bridges on glass substrates. The structural layer of the MEMS bridges is a multilayer blended conductive polymer based on poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) to which functionalized CNT monolayers are electrostatically attached. The resonance frequency (fres) of electrostatically actuated pMEMS bridges was measured as a function of their length (32–67 lm) for different multilayer compositions. A significant increase in fres and quality factor (Q) with the addition of CNT monolayers to the PEDOT:PSS structural material is observed, demonstrating that CNT monolayers can be used to modulate pMEMS resonator properties.Peer ReviewedPostprint (published version

Classical transport equation in non-commutative QED at high temperature

We show that the high temperature behavior of non-commutative QED may be simply obtained from Boltzmann transport equations for classical particles. The transport equation for the charge neutral particle is shown to be characteristically different from that for the charged particle. These equations correctly generate, for arbitrary values of the non-commutative parameter theta, the leading, gauge independent hard thermal loops, arising from the fermion and the gauge sectors. We briefly discuss the generating functional of hard thermal amplitudes.Comment: 11 page

Phase control and measurement of ultrashort optical pulses

We have used the Direct Optical Spectral Phase Measurement (DOSPM) technique to characterize the cubic phase tuning ability of our pulse stretcher. We have compared the measured phase to the phase determined from cross-correlation measurements

Suppression of inhomogeneous broadening in rf spectroscopy of optically trapped atoms

We present a novel method for reducing the inhomogeneous frequency broadening in the hyperfine splitting of the ground state of optically trapped atoms. This reduction is achieved by the addition of a weak light field, spatially mode-matched with the trapping field and whose frequency is tuned in-between the two hyperfine levels. We experimentally demonstrate the new scheme with Rb 85 atoms, and report a 50-fold narrowing of the rf spectrum

Semi-classical Strings in Sasaki-Einstein Manifolds

We find point-like and classical string solutions on the AdS_5 x X^5, where X^5 are the 5-dimensional Sasaki-Einstein manifolds Ypq and Lpqr. The number of acceptable solutions is limited drastically in order to satisfy the constraints on the parameters and coordinates of the manifolds. The energy of the solutions depends on the parameters of the Sasaki-Einstein manifolds and on the conserved momenta transcendentally. A discussion on BPS solutions is presented as well.Comment: 34 pages, 9 figure

Transport equation for the photon Wigner operator in non-commutative QED

We derive an exact quantum equation of motion for the photon Wigner operator in non-commutative QED, which is gauge covariant. In the classical approximation, this reduces to a simple transport equation which describes the hard thermal effects in this theory. As an example of the effectiveness of this method we show that, to leading order, this equation generates in a direct way the Green amplitudes calculated perturbatively in quantum field theory at high temperature.Comment: 13 pages, twocolumn revtex4 styl

Understorey plant community and light availability in conifer plantations and natural hardwood forests in Taiwan

Questions: What are the effects of replacing mixed species natural forests with Cryptomeria japonica plantations on understorey plant functional and species diversity? What is the role of the understorey light environment in determining understorey diversity and community in the two types of forest? Location: Subtropical northeast Taiwan. Methods: We examined light environments using hemispherical photography, and diversity and composition of understorey plants of a 35‐yr C. japonica plantation and an adjacent natural hardwood forest. Results: Understorey plant species richness was similar in the two forests, but the communities were different; only 18 of the 91 recorded understorey plant species occurred in both forests. Relative abundance of plants among different functional groups differed between the two forests. Relative numbers of shade‐tolerant and shade‐intolerant seedling individuals were also different between the two forest types with only one shade‐intolerant seedling in the plantation compared to 23 seedlings belonging to two species in the natural forest. In the natural forest 11 species of tree seedling were found, while in the plantation only five were found, and the seedling density was only one third of that in the natural forest. Across plots in both forests, understorey plant richness and diversity were negatively correlated with direct sunlight but not indirect sunlight, possibly because direct light plays a more important role in understorey plant growth. Conclusions: We report lower species and functional diversity and higher light availability in a natural hardwood forest than an adjacent 30‐yr C. japonica plantation, possibly due to the increased dominance of shade‐intolerant species associated with higher light availability. To maintain plant diversity, management efforts must be made to prevent localized losses of shade‐adapted understorey plants