1,698 research outputs found
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 (32â67 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
Recommended from our members
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 35âyr 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 shadeâtolerant and shadeâintolerant seedling individuals were also different between the two forest types with only one shadeâintolerant 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 30âyr C. japonica plantation, possibly due to the increased dominance of shadeâintolerant species associated with higher light availability. To maintain plant diversity, management efforts must be made to prevent localized losses of shadeâadapted understorey plants
- âŠ