26,433 research outputs found
Tilt-Induced Anisotropic to Isotropic Phase Transition at
A modest in-plane magnetic field \Bpar\ is sufficient to destroy the
fractional quantized Hall states at and 7/2 and replace them with
anisotropic compressible phases. Remarkably, we find that at larger \Bpar\
these anisotropic phases can themselves be replaced by isotropic compressible
phases reminiscent of the composite fermion fluid at . We present
strong evidence that this transition is a consequence of the mixing of Landau
levels from different electric subbands. We also report surprising dependences
of the energy gaps at and 7/3 on the width of the confinement
potential.Comment: Accepted by Phys. Rev. Lett. This is a final version with rewritten
introduction and modified figure
Optical Ultrasound Generation and Detection for Intravascular Imaging: A Review.
Combined ultrasound and photoacoustic imaging has attracted significant interests for intravascular imaging such as atheromatous plaque detection, with ultrasound imaging providing spatial location and morphology and photoacoustic imaging highlighting molecular composition of the plaque. Conventional ultrasound imaging systems utilize piezoelectric ultrasound transducers, which suffer from limited frequency bandwidths and reduced sensitivity with miniature transducer elements. Recent advances on optical methods for both ultrasound generation and detection have shown great promise, as they provide efficient and ultrabroadband ultrasound generation and sensitive and ultrabroadband ultrasound detection. As such, all-optical ultrasound imaging has a great potential to become a next generation ultrasound imaging method. In this paper, we review recent developments on optical ultrasound transmitters, detectors, and all-optical ultrasound imaging systems, with a particular focus on fiber-based probes for intravascular imaging. We further discuss our thoughts on future directions on developing combined all-optical photoacoustic and ultrasound imaging systems for intravascular imaging
Quantization of the diagonal resistance: Density gradients and the empirical resistance rule in a 2D system
We have observed quantization of the diagonal resistance, R_xx, at the edges
of several quantum Hall states. Each quantized R_xx value is close to the
difference between the two adjacent Hall plateaus in the off-diagonal
resistance, R_xy. Peaks in R_xx occur at different positions in positive and
negative magnetic fields. Practically all R_xx features can be explained
quantitatively by a ~1%/cm electron density gradient. Therefore, R_xx is
determined by R_xy and unrelated to the diagonal resistivity rho_xx. Our
findings throw an unexpected light on the empirical resistivity rule for 2D
systems
Monolithic millimeter-wave diode grid frequency multiplier arrays
Monolithic diode frequency multiplier arrays, including barrier-N-N(+) (BNN) doubler, multi-quantum-barrier-varactor (MQBV) tripler, Schottky-quantum-barrier-varactor (SQBV) tripler, and resonant-tunneling-diode (RTD) tripler arrays, have been successfully fabricated with yields between 85 and 99 percent. Frequency doubling and/or tripling have been observed for all the arrays. Output powers of 2.4-2.6 W (eta = 10-18 percent) at 66 GHz with the BNN doubler and 3.8-10 W (eta = 1.7-4 percent) at 99 GHz with the SQBV tripler have been achieved
Hybrid exciton-polaritons in a bad microcavity containing the organic and inorganic quantum wells
We study the hybrid exciton-polaritons in a bad microcavity containing the
organic and inorganic quantum wells. The corresponding polariton states are
given. The analytical solution and the numerical result of the stationary
spectrum for the cavity field are finishedComment: 3 pages, 1 figure. appear in Communications in Theoretical Physic
- …