556 research outputs found
Optomechanics in an ultrahigh-Q two-dimensional photonic crystal cavity
We demonstrate an ultrahigh-Q slotted two-dimensional photonic crystal cavity capable of obtaining strong interaction between the internal light field and the mechanical motion of the slotted structure. The measured optical quality factor is Q = 1.2×10^6 for a cavity with an effective modal volume of V_(eff) = 0.04(λ)^3. Optical transduction of the thermal motion of the fundamental in-plane mechanical resonance of the structure (ν_m = 151 MHz) is performed, from which a zero-point motion optomechanical coupling rate of g∗/2π = 320 kHz is inferred. Dynamical back-action of the optical field on the mechanical motion, resulting in cooling and amplication of the mechanical motion, is also demonstrated
Electrostatically tunable optomechanical "zipper" cavity laser
A tunable nanoscale "zipper" laser cavity, formed from two doubly clamped
photonic crystal nanobeams, is demonstrated. Pulsed, room temperature,
optically pumped lasing action at a wavelength of 1.3 micron is observed for
cavities formed in a thin membrane containing InAsP/GaInAsP quantum-wells.
Metal electrodes are deposited on the ends of the nanobeams to allow for
micro-electro-mechanical actuation. Electrostatic tuning and modulation of the
laser wavelength is demonstrated at a rate of 0.25nm/V^2 and a frequency as
high as 6.7MHz, respectively.Comment: 4 pages, 4 figure
Microstrip resonator for microwaves with controllable polarization
In this work the authors implemented a resonator based upon microstrip
cavities that permits the generation of microwaves with arbitrary polarization.
Design, simulation, and implementation of the resonators were performed using
standard printed circuit boards. The electric field distribution was mapped
using a scanning probe cavity perturbation technique. Electron spin resonance
using a standard marker was carried out in order to verify the polarization
control from linear to circular.Comment: 3 pages, 3 figures, submitted to Appl. Phys. Let
Determination of spin polarization in InAs/GaAs self-assembled quantum dots
The spin polarization of electrons trapped in InAs self-assembled quantum dot
ensembles is investigated. A statistical approach for the population of the
spin levels allows one to infer the spin polarization from the measure values
of the addition energies. From the magneto-capacitance spectroscopy data, the
authors found a fully polarized ensemble of electronic spins above 10 T when
and at 2.8 K. Finally, by including the g-tensor
anisotropy the angular dependence of spin polarization with the magnetic field
orientation and strength could be determined.Comment: 3 pages, 2 figures, Accepted Appl. Phys. Let
Polarization-selective excitation of N-V centers in diamond
The nitrogen-vacancy (N-V) center in diamond is promising as an electron spin
qubit due to its long-lived coherence and optical addressability. The ground
state is a spin triplet with two levels () degenerate at zero
magnetic field. Polarization-selective microwave excitation is an attractive
method to address the spin transitions independently, since this allows
operation down to zero magnetic field. Using a resonator designed to produce
circularly polarized microwaves, we have investigated the polarization
selection rules of the N-V center. We first apply this technique to N-V
ensembles in [100] and [111]-oriented samples. Next, we demonstrate an imaging
technique, based on optical polarization dependence, that allows rapid
identification of the orientations of many single N-V centers. Finally, we test
the microwave polarization selection rules of individual N-V centers of known
orientation
Lande g-tensor in semiconductor nanostructures
Understanding the electronic structure of semiconductor nanostructures is not
complete without a detailed description of their corresponding spin-related
properties. Here we explore the response of the shell structure of InAs
self-assembled quantum dots to magnetic fields oriented in several directions,
allowing the mapping of the g-tensor modulus for the s and p shells. We found
that the g-tensors for the s and p shells show a very different behavior. The
s-state in being more localized allows the probing of the confining potential
details by sweeping the magnetic field orientation from the growth direction
towards the in-plane direction. As for the p-state, we found that the g-tensor
modulus is closer to that of the surrounding GaAs, consistent with a larger
delocalization. These results reveal further details of the confining
potentials of self-assembled quantum dots that have not yet been probed, in
addition to the assessment of the g-tensor, which is of fundamental importance
for the implementation of spin related applications.Comment: 4 pages, 4 figure
Observation of Quantum Motion of a Nanomechanical Resonator
In this Letter we use resolved sideband laser cooling to cool a mesoscopic mechanical resonator to near its quantum ground state (phonon occupancy 2.6±0.2), and observe the motional sidebands generated on a second probe laser. Asymmetry in the sideband amplitudes provides a direct measure of the displacement noise power associated with quantum zero-point fluctuations of the nanomechanical resonator, and allows for an intrinsic calibration of the phonon occupation number
Evaluation on the use of active bearing in internal combustion engines
Orientador: Marco Lucio BittencourtDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecanicaResumo: Legislações mais severas em relação ao consumo de combustÃvel e a redução na emissão de gases estão fazendo com que os motores de combustão interna operem com pressões de combustão cada vez mais elevadas. Como consequencia destas restrições, os mancais são afetados diretamente. Este trabalho tem como principal objetivo estudar a viabilidade do uso de mancais ativos para o aumento do desempenho dos mancais de motores de combustão interna, principalmente na redução de atrito e desgaste. Um conjunto de simulações numéricas em mancais hidrodinâmicos foi realizada para avaliar a influencia no comportamento do filme de oleo a partir da variação da pressão de injeção de lubrificante e sua posição angular em relação ao mancal. Um segundo conjunto de simulações avaliou a influencia no comportamento do filme de oleo de uma descontinuidade e sua posição angular. Essa descontinuidade pode ser considerada um perfilamento na superficie do alojamento do mancal. Uma terceira e quarta series de simulações avaliaram a influencia da magnitude do carregamento e o seu modo, dinamico ou estatico, no comportamento do filme de oleo de mancais com descontinuidade em seu alojamento. Por fim, a partir dos dados gerados nas simulações e nos princÃpios sobre mancais ativos, foi possÃvel avaliar a viabilidade técnica do uso destes tipos de mancais em motores de combustão interna, propondo-se uma configuração básica de um novo mancal ativo.Abstract: Severe legislative requirements on fuel consumption and reduction of exhaust emissions require that the internal combustion engines operate with higher combustion pressures. As a result of these restrictions, the bearings are directly affected. The main objective of this work is the feasibility study on using active bearings to increase the performance of internal combustion engines bearings, primarily to reduce friction and wear.
Numerical simulations of a hydrodynamic bearing were performed to evaluate the behavior of the oil film due to the variation of the oil pressure injection and its angular position in relation to the bearing. A second set of simulations evaluated the behavior of the oil film
due to a discontinuity on the bearing shell and its angular position. This discontinuity can
be considered a profile on the bearing shell surface. A third and fourth series of simulations
evaluated the behavior of the oil film on a bearing shell with discontinuity, influenced by the magnitude of the load and its dynamic or static mode. Finally, from the data generated in simulations and on active bearing principles, it was possible to evaluate the technical feasibility of using these types of bearings in internal combustion engines. A basic configuration for a new active bearing was proposed.MestradoMecânica dos Sólidos e Projeto MecânicoMestre em Engenharia Mecânic
- …