The article is devoted to studying of stress and displacement amplitude distribution in ultrasonic concentrators of different forms. The modelling of different forms of ultrasonic concentrators was ...considered in detail that allowed to choose an optimal form of concentrator providing maximum amplitude of vibrational speed and uniform stress amplitude distribution across the concentrator section. The modelling was carried out for purpose of the subsequent application of ultrasonic treatment to nanostructured materials. Numerical calculation in the environment of MatLab is carried out and diagrams of dependences of stress and displacement amplitude distribution of conic, exponential, ampoule and two-ampoule forms of concentrators are constructed. Visual distribution models of stresses on the section of concentrators and elastic displacements of material in samples of these forms are constructed, resonance frequencies of longitudinal fluctuations of ultrasonic half-wave concentrators are found in the program Abaqus complex.
The Electromechanical Amplitude Modulation (EAM) is frequently used to eliminate feed-through signals between forcer and pick-off electrodes of resonant microstructures. However, there are some ...undesirable effects of EAM that need to be considered. This work studies the contribution of EAM on dissipation of energy and appeared non-linear dynamics in MEMS Coriolis Vibratory Gyroscopes (CVGs). We presented an analytical model, capturing the effect of AC carrier signal on amplitude-frequency coupling, scale factor instability, and in-run noise performance of CVGs. The effect of EAM on a Dynamically Amplified dual-mass Gyroscope (DAG) was experimentally demonstrated and compared to the simulation results of the analytical model. We concluded that the AC carrier signal in EAM influences the amplitude-frequency couplings along both the drive and sense modes of the gyroscope through modifying the non-linear electrostatic stiffnesses, which was also proven to be one of the dominant sources of both the scale factor nonlinearity and frequency instability in the near-mode-matched DAG, operating in the open-loop rate mode.
Deconvolution methods can be applied in airborne scanning radar to enhance its angular resolution for improving the collision avoidance ability in the forward-looking direction. However, as the ...movement speed of the airborne platform increases, the traditional convolution signal model cannot be applied because of the model errors in the amplitude profile and Doppler phase. In this article, an accurate profile-phase deconvolution method is proposed to achieve scanning radar forward-looking super-resolution imaging, particularly for high-speed platforms. On one hand, a profile-phase convolution (PPC) model is established by analyzing the influence of high-speed platform on echo amplitude profile and Doppler phase. The proposed model accurately captures the variation of beam dwell time caused by the coupling of platform motion and beam scanning, which directly affects the echo amplitude profile. On the other hand, relying on the proposed PPC model, an adaptive regularization (AR) deconvolution method is derived to avoid hyperparameter selection. Point-target and surface-target results demonstrate that the proposed PPC model and the AR deconvolution method are competent for super-resolution imaging on high-speed platforms.
This article presents a 60-GHz CMOS power amplifier (PA) with an adaptive impedance-compensation linearizer in the 65-nm CMOS process. The proposed linearizer adaptively provides resistance and ...capacitance that vary appropriately with input power, enabling amplitude-to-amplitude modulation (AM-AM) and amplitude-to-phase modulation (AM-PM) distortions to be compensated simultaneously. The fabricated PA with linearizer on achieves a <inline-formula> <tex-math notation="LaTeX">P_{\mathrm {1\,dB}} </tex-math></inline-formula> of 12.3 dBm and a peak power-added efficiency (PAE) of 15.6% at such <inline-formula> <tex-math notation="LaTeX">P_{\mathrm {1\,dB}} </tex-math></inline-formula>, which demonstrate improvements of 2.8 dB and 6.8%, respectively, compared with the PA with linearizer off. The PA also achieves the peak gain of 31.0 dB, peak saturated power (<inline-formula> <tex-math notation="LaTeX">P_{\mathrm {SAT}} </tex-math></inline-formula>) of 15.0 dBm, and peak PAE max of 22.7%. In addition, the AM-AM distortion at 6-dB output back-off (OBO) is less than 0.1 dB, and the AM-PM distortion at <inline-formula> <tex-math notation="LaTeX">P_{\mathrm {1\,dB}} </tex-math></inline-formula> is less than 1.5° in the overall 3-dB frequency band. The improvements in both the AM-AM and AM-PM signals lead to a 1.7-dB improvement in OBO at third-order intermodulated distortion of −25 dBc without adding to power consumption.
Interpreting EEG alpha activity Bazanova, O M; Vernon, D
Neuroscience and biobehavioral reviews,
07/2014, Volume:
44
Journal Article
Peer reviewed
Open access
Exploring EEG alpha oscillations has generated considerable interest, in particular with regards to the role they play in cognitive, psychomotor, psycho-emotional and physiological aspects of human ...life. However, there is no clearly agreed upon definition of what constitutes 'alpha activity' or which of the many indices should be used to characterize it. To address these issues this review attempts to delineate EEG alpha-activity, its physical, molecular and morphological nature, and examine the following indices: (1) the individual alpha peak frequency; (2) activation magnitude, as measured by alpha amplitude suppression across the individual alpha bandwidth in response to eyes opening, and (3) alpha "auto-rhythmicity" indices: which include intra-spindle amplitude variability, spindle length and steepness. Throughout, the article offers a number of suggestions regarding the mechanism(s) of alpha activity related to inter and intra-individual variability. In addition, it provides some insights into the various psychophysiological indices of alpha activity and highlights their role in optimal functioning and behavior.
Analysis of seismic data suggests that hydrocarbon deposits are often associated with higher than usual values of attenuation, but this is generally ignored during amplitude versus offset (AVO) ...analysis. The effect can be modelled with equivalent medium theory based on the squirt flow concept, but the excess attenuation is associated with strong velocity dispersion. Consequently, when we study reflections from the interface between such an equivalent medium and an elastic overburden we find that the reflection coefficient varies with frequency. The impact of this variation depends on the AVO behaviour at the interface; class I reflections tend to be shifted to higher frequency while class III reflections have their lower frequencies amplified. We calculate synthetic seismograms for typical models using the reflectivity method for materials with frequency dependent velocities and attenuations, and find that these effects are predicted to be detectable on stacked data. Two field data sets show frequency anomalies similar to those predicted by the analysis, and we suggest that our modelling provides a plausible explanation of the observations.
Shallow crustal velocity and Poisson's ratio structures are of key importance to understand rock properties and near‐surface tectonic deformation and evolution. We propose a novel imaging method to ...acquire such information at individual stations by joint inversion of amplitude ratios between the horizontal and vertical components of both teleseismic P and S waves. Our synthetic experiments demonstrate the validity of the method in recovering subsurface structures up to ∼8–10 km depth. We apply this method to construct the velocity and Poisson's ratio images along a NW‐SE‐trending seismic array within the Sichuan Basin, southwestern China. The results reveal well developed stratification and localized high Poisson's ratio anomalies, which reflect a long‐term stable sedimentary environment and fault‐related deformation in response to the Cenozoic Tibet–basin collision, consistent with geological observations. Our new method builds a bridge between fine‐scale near‐surface seismic exploration and large‐scale deep passive‐source imaging, especially for areas of weak seismicity.
Plain Language Summary
Both seismic wave travel time and amplitude bear important information on subsurface structures and can therefore be used to image them. Travel time is commonly used in conventional seismic imaging methods, whose imaging accuracy, however, is heavily dependent on the distribution of stations and/or events. Amplitude is rarely taken into account when imaging because of poorly understood information about complex source functions. Here, we propose to utilize amplitude ratios between the horizontal and vertical components of teleseismic body waves to image the subsurface velocity and Poisson's ratio structures at individual stations. Our new method does not require any source information or high‐density raypath coverage and provides an intermediate approach between fine‐scale (∼km) near‐surface seismic exploration and large‐scale (several tens to hundreds and thousands of kilometers) deep passive‐source imaging. Considering today's abundant broadband seismic data around the world, this method is promising for their further reutilization.
Key Points
Joint inversion of P and S wave amplitude ratios enables the better recovery of the shallow crustal velocity and Poisson's ratios
Lateral traceability of strongly stratified structures may reflect a long‐term stable sedimentary environment within the Sichuan Basin
The Cenozoic Tibet–Sichuan Basin collision may have led to fault‐related deformation localized in the sedimentary cover of the basin
Four level pulse amplitude modulation (PAM-4) has become the modulation format of choice to replace on-off keying (OOK) for the 400 Gb/s short reach optical communications systems. In this paper, we ...investigate the possible modifications to conventional Mach-Zehnder modulator structures to improve the system performance. We present three different silicon photonic Mach-Zehnder modulator architectures for generating PAM-4 in the optical domain using OOK electrical driving signals. We investigate the transfer function and linearity of each modulator and experimentally compare their PAM-4 generation and transmission performance with and without use of digital signal processing (DSP). We achieve the highest reported PAM-4 generation and transmission without the use of DSP. The power consumption of each modulator is presented, and we experimentally show that multielectrode Mach-Zehnder modulators provide a clear advantage at higher symbol rates compared to conventional Mach-Zehnder modulators.
Recent advances in the retrieval of Chl fluorescence from space using passive methods (solar-induced Chl fluorescence, SIF) promise improved mapping of plant photosynthesis globally. However, ...unresolved issues related to the spatial, spectral, and temporal dynamics of vegetation fluorescence complicate our ability to interpret SIF measurements.
We developed an instrument to measure leaf-level gas exchange simultaneously with pulse-amplitude modulation (PAM) and spectrally resolved fluorescence over the same field of view – allowing us to investigate the relationships between active and passive fluorescence with photosynthesis.
Strongly correlated, slope-dependent relationships were observed between measured spectra across all wavelengths (Fλ
, 670–850 nm) and PAM fluorescence parameters under a range of actinic light intensities (steady-state fluorescence yields, F
t) and saturation pulses (maximal fluorescence yields, F
m). Our results suggest that this method can accurately reproduce the full Chl emission spectra – capturing the spectral dynamics associated with changes in the yields of fluorescence, photochemical (ΦPSII), and nonphotochemical quenching (NPQ).
We discuss how this method may establish a link between photosynthetic capacity and the mechanistic drivers of wavelength-specific fluorescence emission during changes in environmental conditions (light, temperature, humidity). Our emphasis is on future research directions linking spectral fluorescence to photosynthesis, ΦPSII, and NPQ.
For short range optical transmissions, the intensity modulation and direct detection (IM/DD) offers the advantages of low cost and low complexity. In this paper, we will review our recent ...investigation results about IM/DD schemes such as polybinary and discrete multitone (DMT). Polybinary four-level pulse amplitude modulation (PAM-4) system shows better performance than the conventional PAM-4 system for both multimode and single-mode fibers. If the electrical dispersion compensation (EDC) is conducted with DDMZM, the reachable distance can be extended to 80 km which is suitable for the metro access scenario. Single sideband (SSB) polybinary-PAM-4 is also feasible to greatly increase the spectral efficiency (SE) and system capacity. Also, some DMT architectures for metro applications without using dispersion compensating modules will be introduced. SSB-DMT is very simple, while chromatic dispersion (CD) calculation and pre-compensation are not necessary. EDC double sideband (DSB) DMT owns 3-dB better performance than the SSB-DMT. CD can be calculated according to the power fading and the result is sent back to the transmitter for pre-compensation. Twin-SSB-DMT has the highest SE. More than 200-Gb/s data have been successfully generated and transmitted over 80 km single mode fiber (SMF).
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