Phase Asymmetries Research Articles

A vector intermodulation analyzer applied to behavioral modeling of nonlinear amplifiers with memory

A large signal vector intermodulation network analyzer with a dynamic range of 90 dB and phase resolution of better than 2/spl deg/ is reported. The analyzer is used in conjunction with a multislice behavioral model to characterize memory effects in three different RF power amplifiers: an MOSFET instrumentation amplifier, a multistage GaAs/silicon-based broadband microwave integrated-circuit amplifier, and an SiGe HBT monolithic-microwave integrated-circuit amplifier. The multislice behavioral model architecture builds on conventional single-tone AM-AM and AM-PM modeling extended to capture long-term memory effects that are characterized by asymmetric intermodulation distortion (IMD). Phase asymmetries of upper and lower IMD are captured. A systematic procedure for extracting the model is presented.

IM3 and IM5 phase characterization and analysis based on a simplified Newton approach

A simplified Newton method is developed to deduce closed-form expressions for two-tone third- and fifth-order intermodulation magnitude and phase predictions in nonlinear microwave circuits, taking advantage of the attractive convergence properties of Newton-based algorithms. The new approach has provided theoretical data for comparison with experimental results acquired with an automated setup for the characterization of phase asymmetries in two-tone measurements. The empirical method generates the tones in a coherent form and supports the evaluation of effects dependent on baseband impedance and tone separation. A high electron-mobility transistor amplifier under two-tone excitation has been widely characterized using the experimental setup, and measurements have been compared with simulated data showing a good agreement. The theoretical method is empowered with its capability to predict fifth-order effects in a form simpler than the conventional Volterra-series approach

Quark recombination and elliptic flow

Elliptic flow systematics for different hadron species have been explained by quark coalescence models. It has been argued that the elliptic asymmetry v_2 should scale with the number of quarks that comprise the hadron. We show how these arguments are sensitive to the relative role of asymmetries in the phase space density vs. asymmetries in the effective volume of emission. We also discuss the degree to which coalescence arguments differ from thermal models. Illustrative calculations based on solving the Boltzmann equation are presented along with the results of blast-wave models. Although the issue is complicated, ambiguities might be clarified by measurements of source-size parameters for nucleons at higher transverse momenta.

Seasonal-longitudinal variability of equatorial plasma bubbles

Abstract. We compare seasonal and longitudinal distributions of more than 8300 equatorial plasma bubbles (EPBs) observed during a full solar cycle from 1989-2000 with predictions of two simple models. Both models are based on considerations of parameters that influence the linear growth rate, γRT, of the generalized Rayleigh-Taylor instability in the context of finite windows of opportunity available during the prereversal enhancement near sunset. These parameters are the strength of the equatorial magnetic field, Beq, and the angle, α, it makes with the dusk terminator line. The independence of α and Beq from the solar cycle phase justifies our comparisons. We have sorted data acquired during more than 75000 equatorial evening-sector passes of polar-orbiting Defense Meteorological Satellite Program (DMSP) satellites into 24 longitude and 12 one-month bins, each containing ~250 samples. We show that: (1) in 44 out of 48 month-longitude bins EPB rates are largest within 30 days of when α=0°; (2) unpredicted phase shifts and asymmetries appear in occurrence rates at the two times per year when α≈0°; (3) While EPB occurrence rates vary inversely with Beq, the relationships are very different in regions where Beq is increasing and decreasing with longitude. Results (2) and (3) indicate that systematic forces not considered by the two models can become important. Damping by interhemispheric winds appears to be responsible for phase shifts in maximum rates of EPB occurrence from days when α=0°. Low EPB occurrence rates found at eastern Pacific longitudes suggest that radiation belt electrons in the drift loss cone reduce γRT by enhancing E-layer Pedersen conductances. Finally, we analyze an EPB event observed during a magnetic storm at a time and place where α≈-27°, to illustrate how electric-field penetration from high latitudes can overwhelm the damping effects of weak gradients in Pedersen conductance near dusk.

Lateral Phase Mucosal Wave Asymmetries in the Clinical Voice Laboratory

Summary: Anecdotally, in some persons it has been observed by the Senior Author (K.K.) that asymmetries of the mucosal wave exist when examined videostroboscopically. In the vast majority of these people, no pathology is ever discovered. Mucosal wave asymmetries could cause concern for the otolaryngologist, who may consider them to be a forewarning of subclinical pathology and subject the patient to unnecessary, expensive, and anxiety-provoking investigations or interventions. The purpose of this study was to establish the prevalence of mucosal wave asymmetries in an asymptomatic population lacking laryngeal pathology. Acoustic spectral analysis is also utilized to determine if the presence of subharmonics might be associated. A hospital-based, cross-sectional study design was used. The subjects had no known vocal or medical pathologies, and were nonsmoking. The study group was composed of 30 males aged 35–50 years and 30 women between 22–55 years. Each of the males underwent acoustic spectral analysis; and all subjects completed a medical questionnaire, subjective talkativeness rating, and videostroboscopic laryngeal examination. 10.5% of the subjects (exact 95% CI = 4.0–21.5%) exhibited mucosal wave variations at stroboscopy, characterized as periodic lateral phase asymmetries found consistently in both the modal and upper registers. There was no association with the chosen acoustic spectral parameters, talkativeness scales, or questionnaire-based variables. Mucosal wave asymmetries may be a variance of normal, and are likely to be far more common in the general population than previously believed. The prevalence detected here is expected to be important in the clinical laryngology practice, where these asymmetries may be frequently encountered and influencing management decisions. There has been little normative data published for variations of the mucosal wave specifically for epidemiological purposes. Clinically, in the absence of such data, otolaryngologists may over interpret videostroboscopic findings, leading to unnecessary investigations or interventions.

Mucosal wave asymmetries in the clinical voice laboratory.

Anecdotally, it has been observed that in some healthy middle-aged men, who have neither vocal complaints nor known vocal pathology, asymmetries of the mucosal wave exist when examined videostroboscopically. This may cause concern on the part of the otolaryngologist, who might consider mucosal wave asymmetries to be a forewarning of subclinical pathology and subject the patient to unnecessary, expensive, and anxiety-provoking investigations or interventions. The purpose of this study is to establish the presence of mucosal wave asymmetries in a healthy, asymptomatic subpopulation. Acoustic spectral analysis is also used to determine if the presence of subharmonics might be associated. A prospective, cohort study design was used. The population was randomly selected, healthy, asymptomatic, nonsmoking men aged 35 to 50 years. Each subject completed acoustic spectral analysis and a medical questionnaire, followed by videostroboscopic laryngeal examination. Thirty-seven percent of the subjects exhibited mucosal wave variations at stroboscopy, characterized as periodic lateral phase asymmetries. There was no association with the acoustic spectral parameters chosen. Mucosal wave asymmetries may be a variance of normal. The 37% found here is expected to be very significant. Mucosal wave asymmetries are likely to be far more common in the general population than previously believed. There have been few normative data published for variations of the mucosal wave specifically for epidemiologic purposes. These results establish a starting point and justification for the normative population studies under way at our institution. Clinically, in the absence of such data, otolaryngologists may overinterpret videostroboscopic findings, leading to unnecessary investigations or interventions.

Effects of mean winds and dissipation on the diurnal propagating tide: An analytic approach

The effects of mean winds and dissipation on the vertical and horizontal structures of the diurnal propagating tide are investigated analytically using a set of “modified” (complex) Hough functions, velocity expansion functions, and equivalent depths. These are derived by introducing a doppler-shifted complex frequency σ ∗ into the “large ϵ” approximation of Longuet-Higgins (1968, Phil. Trans. R. Soc. (London) A262, 511) for his “Type 1” waves. An equivalent result can be obtained by utilizing an equatorial betaplane approximation. The imaginary part of σ ∗ represents effective Rayleigh friction and Newtonian cooling coefficients which parameterize diffusion of momentum (mechanical dissipation) and heat (thermal dissipation), respectively, and the real part of σ ∗ is doppler-shifted according to an average (latitude-dependent) zonal wind speed. Our results are utilized to interpret salient features of recent numerical simulations of the propagating diurnal tide, including formation of an amplitude peak near 90 km, coupling into evanescent modes above this altitude, amplitude and phase asymmetries about the equator, and amplitude broadening with latitude. We suggest that these functions can be utilized to interpret tidal observations in the 70–100 km region, and perhaps to serve as basis functions for fitting (decomposing) such data from a latitude chain of stations.

Frequency-dependent AC system equivalents for harmonic studies and transient convertor simulation

A technique for the the generalization of the impedance loci is described. This technique is capable of displaying the complete frequency response of any given power system including multiphase-related effects such as phase asymmetries and mutual couplings. This information is used to derive frequency-dependent equivalent circuits suitable for integration in the time-domain solutions of power-system waveforms. Direct and optimization techniques are used in the derivation of the equivalent circuits. Their effects on impedance frequency matching and computational efficiency are compared.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The postnatal development of monocular optokinetic nystagmus in infants

Monocular optokinetic nystagmus (OKN) was studied in 24 human infants aged 3–35 weeks using electro-oculography and moving vertical gratings. At a constant velocity of 25 deg/sec, infants display direction-dependent slow phase asymmetries until approximately 5 months after birth. A comparison was made of the cumulative eye displacement during the slow phases of OKN for nasal and temporal movement. A preliminary report of these findings has appeared previously (Naegele J.R. and Held R., 1980) ARVO Annual Meeting, Orlando, FL.