Main Coupling Mechanism Research Articles

Observation of magnetic Feshbach resonances between Cs and Yb173

We report the observation of magnetic Feshbach resonances between $^{173}\mathrm{Yb}$ and $^{133}\mathrm{Cs}$. In a mixture of Cs atoms prepared in the $(f=3,{m}_{f}=3)$ state and unpolarized fermionic $^{173}\mathrm{Yb}$, we observe resonant atom loss due to two sets of magnetic Feshbach resonances around 622 and 702 G. Resonances for individual Yb nuclear spin components ${m}_{i,\mathrm{Yb}}$ are split by its interaction with the Cs electronic spin, which also provides the main coupling mechanism for the observed resonances. The observed splittings and relative resonance strengths are in good agreement with theoretical predictions from coupled-channel calculations.

NiFe/CoFe/Cu/CoFe/MnIr spin valves studied by ferromagnetic resonance

Ion-beam deposited (Glass/Ta/NiFe/CoFe/Cu/CoFe/MnIr/Ta) spin valves (SVs) with a Cu-spacer thickness (tCu) varying from 14 to 28 Å have been studied by ferromagnetic resonance (FMR) and magnetoresistance (MR) measurements. With respect to the interlayer coupling strength between the free and fixed ferromagnetic layers, the samples have been divided in those with a weak coupling (for tCu > 16 Å) and a strong coupling regimes (for tCu ≤ 16 Å). The FMR behavior in these two regimes is quite different. For the weakly coupled series, there are two well-defined FMR peaks stemming from the free and fixed layers. Their in-plane angular dependences exhibit 180° and 360° symmetries, respectively. For the strongly coupled SVs, the resonance modes are hybridized and possess features of both layers simultaneously. The main coupling mechanism between the two layers, as concluded from the FMR and MR measurements, is the Néel “orange-peel” magnetostatic interaction, accompanied by a direct exchange due to pinholes in the Cu spacer for tCu < 17 Å.

Optical investigations on single vertically coupled InP/GaInP quantum dot pairs

AbstractSingle vertically stacked pairs of InP quantum dots (QDs) with different interdot barrier width are investigated using microphotoluminescence, photoluminescence excitation spectroscopy and time‐resolved techniques. The results indicate unidirectional carrier tunneling to be the main coupling mechanism between the two layers containing QDs with intentionally different size. The coupling is changing from electron–hole tunneling to electron tunneling and finally vanishing tunneling with increasing barrier size.magnified image Two QDs of different size form an asymmetric QD molecule with different ground state energies of the composing single QDs. Carriers can tunnel from the small dot to the large dot depending on the interdot spacer thickness dsp.

Characterization of the Virgo seismic environment

The Virgo gravitational wave detector is an interferometer (ITF) with 3 km arms located in Pisa, Italy. From July to October 2010, Virgo performed its third science run (VSR3) in coincidence with the LIGO detectors. Despite several techniques adopted to isolate the ITF from the environment, seismic noise remains an important issue for Virgo. Vibrations produced by the detector infrastructure (such as air conditioning units, water chillers/heaters, pumps) are found to affect Virgo’s sensitivity, with the main coupling mechanisms being through beam jitter and scattered light processes. The Advanced Virgo design seeks to reduce ITF couplings to environmental noise by having most vibration-sensitive components suspended and in vacuum, as well as muffle and relocate loud machines. During the months of June and July in 2010, a Güralp-3TD seismometer was stationed at various locations around the Virgo site hosting major infrastructure machines. Seismic data were examined using spectral and coherence analysis with seismic probes close to the detector. The primary aim of this study was to identify noisy machines which seismically affect the ITF environment and thus require mitigation attention. Analyzed machines are located at various distances from the experimental halls, ranging from 10 to 100 m. An attempt is made to measure the attenuation of emitted noise at the ITF and correlate it with the distance from the source and with seismic attenuation models in soil.

Analysis of Simultaneous Switching Noise Coupling in Multilayer Power/Ground Planes With Segmentation Method and Cavity Model

An accurate power bus model is essential for predicting noise coupling in high-speed printed circuit board (PCB) and package designs. With a complex multilayer structure, the power bus is often modeled using numerical simulation methods. However, full-wave approaches are computationally inefficient, or even infeasible for extremely complicated geometries. Fortunately, the segmentation method makes it possible to combine different types of models together, and both simulation accuracy and efficiency can be obtained through this “divide-and-conquer” strategy. After segmentation, one of the fundamental blocks is a parallel plane pair. For this block, analytical expressions for the impedance ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> ) matrix are available for a rectangular plane pair and some special triangular plane pairs. The combination of the cavity model with the segmentation technique has been known to be an efficient way to analyze irregularly shaped multilayer structures. In this paper, this approach is further extended to the general multilayer structures with overlapping planes. Noise-coupling mechanisms are then studied, and the two main coupling mechanisms, the plane edge coupling and the via coupling, are further characterized. Engineering implications on reducing noise coupling in a practical multilayer PCB are discussed through a series of simulation examples.

Temperature dependence of the coupling between n-type δ-doping region and quantum dot assemblies

We present experimental evidence that at room temperature the main coupling mechanism between an n-type δ-doping region and an adjacent plane of dots is energy-conserving electron-electron scattering, in which a hot electron in the δ-doping region transfers energy to a deeply confined electron in that region and relaxes to the quantum dot. We demonstrate that at room temperature the increased capture cross section due to electron-electron scattering considerably enhances the injection into the quantum dots with a certain size and thus reduces the phonon bottleneck in quantum dot assemblies for the quantum dots that interact with the δ-doping region. We identify different temperature-dependent injection schemes by comparing the photoluminescence of dilute and dense assemblies with the corresponding photoluminescence of similar structures including n-type δ-doping regions adjacent to the dots’ plane.

Static response of thin-walled composite I-beams loaded at their free-end cross-section: analytical solution

Analytical solutions for the static response of anisotropic composite I-beams loaded at their free end are presented. The analysis is accomplished within the framework of the theory of composite thin-walled beams featuring the two main coupling mechanisms, namely, circumferentially uniform stiffness (CUS) and circumferentially asymmetric stiffness (CAS) configurations. Within each of these two configurations, the implications of the directionality property of composite materials, of warping inhibition and transverse shear on the static response of I-beams are highlighted, and final conclusions are outlined.

Stimulus artifact reduction in evoked potential measurements

Objective: To investigate the main coupling mechanisms involved in stimulus artifact contamination of evoked potential recordings and to suggest techniques that minimize this interference. Design: A before-after trial of a single subject. Setting: Measurements were obtained at a university biomedical engineering laboratory. Participants: Data were obtained from one volunteer subject. Intervention: An electrical stimulus was used to depolarize the posterior tibial nerve at the ankle. Various recording electrode configurations were used to demonstrate stimulus artifact recordings. Results: Three mechanisms are defined as contributing significantly to stimulus artifact contamination of evoked potential data. These are: the volume conducted component, the displacement current component, and the electromagnetic coupling component. When each component is maximally controlled, the problem of stimulus artifact is greatly reduced. Conclusion: Three major factors that contribute to stimulus artifact contamination of the evoked potential waveform can be identified and minimized by relatively simple clinical techniques.

Analysis of shielded-room error for screened rooms and its application to low-frequency emission measurements from electrically small sources

Screened rooms are an alternative to open area test sites for radiative emission measurements. The cost of screened anechoic rooms by comparison is considerable, especially for low-frequency operation. The paper considers the use of screened rooms operated below resonance in obtaining low-frequency emission measurements from electrically-small sources. The screened room is modelled as a lossless rectangular cavity using a rapidly convergent Green's function formulation. This is used to establish the shielded-room error for electric and magnetic current sources and examine the main coupling mechanisms between the source and observation point in a screened room. Emission measurements are presented for a self-contained electrically-small test source. Comparison with open-air measurements and emission measurements from a TEM cell show agreement to within ± 5 dB.

Feedback-induced noise in crossed field devices

A guiding center fluid model involving a single RF mode of slowly varying amplitude and phase is used to study the long-time behavior of a distributed emission, reentrant crossed-field amplifier. The space charge recirculation through the drift space provides the main coupling mechanism between the output and the input. The output fluctuations among successive tube passes in the RF power, phase shift and hub density generate a narrow bandwidth around the carrier. By fixing the external control parameters and varying the secondary emission coefficient or the recirculating hub charge fraction, the pass-to-pass fluctuations exhibit transitions from steady-state to periodic limit cycles and finally to unpredictable, chaotic behavior. It is shown that the development of chaotic output patterns is connected with slow, large-amplitude hub density oscillations during a single pass. Analysis shows that the nonlinear and time-delay effects characterizing the hub density evolution cause unstable, oscillatory behavior. The influence of excess space charge accumulation on the tube intrinsic noise is discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>