Perturbation Indices Research Articles

Assessment of the capabilities and applicability of ionospheric perturbation indices provided in Europe

Perturbations in the ionosphere are of great interest not only for scientific research, but also for applications using transionospheric radiosignals (e.g. GNSS applications and HF communication), because the transmission of radiosignals is sensitive to the electron density in the ionosphere. However, ionospheric perturbations have manifold character. Their spatial range can vary between global and very local effects (a few hundreds of km range) and their temporal range varies between seconds and days. All these perturbations have different physical background and different impact on applications. Many ionosphere perturbation indices that characterize the state of ionospheric perturbations have been introduced in the past (e.g. ROTI, S4, σPhi, AATR, Reff, W-index, SISTED, SOLERA, DIXSG, IBI, Dfu/Dfl, etc.). This manuscript is an assessment of a subset of diverse ionospheric indices developed and/or applied in Europe. It describes the objectives of the indices, demonstrates their character in a case study for September 2017, indicates their applicability for different use cases in science and industry and guides users to find the appropriate index for their purposes.

Ionospheric perturbation indices based on the low- and high-orbiting satellite radio tomography data

Methods are suggested for constructing ionospheric perturbation indices (IPIs) based on empirical radio tomographic (RT) electron density distributions taking into account spatiotemporal resolution, and coverage of low- and high-orbiting (LO and HO) RT data. The LORT-based IPIs are calculated as spatial root mean square values of electron density derivatives indicating the presence of local ionospheric structures on a spatial scale of dozens of kilometers. The HORT-based IPIs are based on the statistical characteristics, i.e., means and deviations from the means, of electron density or vertical TEC distributions with different normalizations and subsequent spatial averaging, which take into account the geomagnetic activity and seasonal behavior of ionospheric plasma. Various schemes of IPIs construction are considered, correlations between IPIs and geomagnetic Kp index are analyzed, the indices most sensitive to geomagnetic activity are identified, and additional modifications of computational algorithms enhancing this sensitivity are suggested.

Beta Responses in Healthy Elderly and in Patients With Amnestic Mild Cognitive Impairment During a Task of Temporal Orientation of Attention.

Recent studies demonstrated that beta oscillations are elicited during cognitive processes. To investigate their potential as electrophysiological markers of amnestic mild cognitive impairment (aMCI), we recorded beta EEG activity during resting and during an omitted tone task in patients and healthy elderly. Thirty participants were enrolled (15 patients, 15 healthy controls). In particular, we investigated event-related spectral perturbation and intertrial coherence indices. Analyses showed that ( a) healthy elderly presented greater beta power at rest than patients with aMCI patients; ( b) during the task, healthy elderly were more accurate than aMCI patients and presented greater beta power than aMCI patients; ( c) both groups showed qualitatively similar spectral perturbation responses during the task, but different spatiotemporal response patterns; and ( d) aMCI patients presented greater beta phase locking than healthy elderly during the task. Results indicate that beta activity in healthy elderly differs from that of patients with aMCI. Furthermore, the analysis of task-related EEG activity extends evidences obtained during resting and suggests that during the prodromal phase of Alzheimer's disease there is a reduced efficiency in information exchange by large-scale neural networks. The study for the first time shows the potential of task-related beta responses as early markers of aMCI impairments.

Reliable acoustic measurements in children between 5;0 and 9;11 years: Gender, age, height and weight effects on fundamental frequency, jitter and shimmer in phonations without and with controlled voice SPL

BackgroundCurrent pediatric voice assessment guidelines include instrumental measurements of fundamental frequency (F0) and the perturbation indices jitter and shimmer. In children below 10 years, gender, age, height and weight effects on these parameters have been inconsistently characterized. Recent research in healthy children showed, that differences in habitual speaking voice intensity (voice SPL) under the usual assessment procedure significantly affect jitter and shimmer. These effects were reduced in phonations with controlled voice SPL >80dBA. Reliable measurement methods and description of physiologic influencing factors are essential to identify pathologic voices. ObjectiveThis cross-sectional single cohort study investigates in children between 5;0 and 9;11 years how gender, age, height and weight affect voice F0, jitter and shimmer in phonations at individually “medium” voice intensity (modeling the usual clinical practice) and with controlled voice SPL >80dBA. Subjects and methods68 vocally healthy children (39 f/29 m) aged 5;0–9;11 years provided 3 prolonged phonations of/a/at individually “medium” and controlled voice intensity at “>80dBA” (visual feedback, 10cm distance). F0 (Hz), jitter (%), shimmer (%) and voice SPL (dBA) were determined with PRAAT. Gender, age, height and weight effects without and with controlled voice SPL were assessed by descriptive statistics, Analysis of Variance and Linear Mixed Models. ResultsF0 (Hz), jitter (%), shimmer (%) and voice SPL (dBA) were significantly different in medium voice compared to >80dBA (p<0.01). In medium phonations girls had a higher F0 than boys (girls: 276.7(50.7), boys: 261.5(33.7)), but with >80dBA this difference was only minimal (girls: 328.9(52.2), boys 327.9(51.2)). Mean jitter (0.27(0.10)) and shimmer (4.34(1.68)) were smaller and showed less spread (jitter: 0.5(0.26); shimmer: 9.47(3.47)) with >80dBA. Gender, age, height and weight had no significant effects on F0, jitter, shimmer and voice SPL in both phonation types (p-range=0.42–0.99). ConclusionsNeither without nor with controlled voice SPL there were systematic gender, age, height or weight effects on voice F0, jitter and shimmer. Gender related F0 discrepancies were equalized in phonations with >80dBA. In children below 10 years gender related acoustic voice differences may be mainly linked to behavior, which should be considered in future works regarding physiologic voice development.

Nonlinear Dynamic-Based Analysis of Severe Dysphonia in Patients With Vocal Fold Scar and Sulcus Vocalis

The primary goal of this study was to evaluate a nonlinear dynamic approach to the acoustic analysis of dysphonia associated with vocal fold scar and sulcus vocalis. Case-control study. Acoustic voice samples from scar/sulcus patients and age-/sex-matched controls were analyzed using correlation dimension (D2) and phase plots, time-domain based perturbation indices (jitter, shimmer, signal-to-noise ratio [SNR]), and an auditory-perceptual rating scheme. Signal typing was performed to identify samples with bifurcations and aperiodicity. Type 2 and 3 acoustic signals were highly represented in the scar/sulcus patient group. When data were analyzed irrespective of signal type, all perceptual and acoustic indices successfully distinguished scar/sulcus patients from controls. Removal of type 2 and 3 signals eliminated the previously identified differences between experimental groups for all acoustic indices except D2. The strongest perceptual-acoustic correlation in our data set was observed for SNR and the weakest correlation was observed for D2. These findings suggest that D2 is inferior to time-domain based perturbation measures for the analysis of dysphonia associated with scar/sulcus; however, time-domain based algorithms are inherently susceptible to inflation under highly aperiodic (ie, type 2 and 3) signal conditions. Auditory-perceptual analysis, unhindered by signal aperiodicity, is therefore a robust strategy for distinguishing scar/sulcus patient voices from normal voices. Future acoustic analysis research in this area should consider alternative (e.g., frequency- and quefrency-domain based) measures alongside additional nonlinear approaches.

Half of the T‐cell repertoire combinatorial diversity is genetically determined in humans and humanized mice

In humanized mice, the T-cell repertoire is derived from genetically identical human progenitors in distinct animals. Thus, careful comparison of the T-cell repertoires of humanized mice with those of humans may reveal the contribution of genetic determinism on T-cell repertoire formation. Here, we performed a comprehensive assessment of the distribution of V-J combinations of the human β chain of the T-cell receptor (hTRBV) in NOD.SCID.γc(-/-) (NSG) humanized mice. We observed that numerous V-J combinations were equally distributed in the thymus and in the periphery of humanized mice compared with human references. A global analysis of the data, comparing repertoire perturbation indices in humanized NSG mice and unrelated human PBMCs, reveals that 50% of the hTRBV families significantly overlapped. Using multivariate ranking and bootstrap analyses, we found that 18% of all possible V-J combinations contributed close to 50% of the expressed diversity, with significant over-representation of BV5-J1.1+1.2 and BV6-J1.1+1.2 rearrangements. Finally, comparison of CD3(-) and CD3(+) thymocyte repertoires indicated that the observed V-J combination overlap was already present before TCR-MHC selection in the thymus. Altogether, our results show that half of the T-cell repertoire combinatorial diversity in humans is genetically determined.

Microphysics and heterogeneous chemistry in aircraft plumes - high sensitivity on local meteorology and atmospheric composition

Abstract. An aircraft plume model has been developed on the basis of two coupled trajectory box models. Two boxes, one for plume and one for background conditions, are coupled by means of a mixing parameterization based on turbulence theory. The model considers comprehensive gas phase chemistry for the tropopause region including acetone, ethane and their oxidation products. Heterogeneous halogen, N2O5 and HOx chemistry on various types of background and aircraft-induced aerosols (liquid and ice) is considered, using state-of-the-art solubility dependent uptake coefficients for liquid phase reactions. The microphysical scheme allows for coagulation, gas-diffusive particle growth and evaporation, so that the particle development from 1s after emission to several days can be simulated. Model results are shown, studying emissions into the upper troposphere as well as into the lowermost stratosphere for contrail and non-contrail conditions. We show the microphysical and chemical evolution of spreading plumes and use the concept of mean plume encounter time, tl, to define effective emission and perturbation indices (EEIs and EPIs) for the North Atlantic Flight Corridor (NAFC) showing EEI(NOy) and EPI(O3) for various background conditions, such as relative humidity, local time of emission, and seasonal variations. Our results show a high sensitivity of EEI and EPIs on the exact conditions under which emissions take place. The difference of EEIs with and without considering plume processes indicates that these processes cannot be neglected.

Vocal fatigue in young trained singers across a solo performance: a preliminary study

This preliminary study aimed to measure changes in vocal function across a solo vocal performance task. Five participants, all trained singers, were required to complete a 10-min standard vocal warm-up, sing from a familiar repertoire for 40 min, and rest their voices for 10 min. Vocal function data were collected at 10-min intervals throughout the experimental session. Acoustic perturbation, sound pressure level and semitone pitch indices were employed as objective vocal function measures. A visual analogue scale and checklist of vocal fatigue symptoms were employed as self-report measures. Results revealed individual variation in vocal endurance, suggesting the importance of vocal history and repertoire factors in predisposing the onset of fatigue. Sound pressure level and pitch indices appeared more useful than perturbation indices in reflecting meaningful trends in vocal change.

Perturbation versus Differentiation Indices

We discuss the relation between perturbation and differentiation indices for overdetermined systems of differential equations based on the formal theory. We show how the Cartan normal form of an involutive system can be used to extend the notion of an underlying equation from differential algebraic equations to partial differential equations. This allows us to generalise results of Campbell and Gear on the relation between perturbation and differentiation indices to systems of partial differential equations.

Resilience of forested wetlands located in the southeastern United States: Demonstration of a soil perturbation index

This study examined the usefulness of soil organic matter (SOM), total organic carbon (TOC), total Kjeldahl nitrogen (TKN), and total phosphorus (TP) as indicators of resilience in forested wetlands located within southeast Virginia, USA. These data were also examined as standards for reference wetlands before and after timber harvesting and for comparisons of mature and early successional stages. Results indicate that the wetland soils in this study seem to be relatively resilient to perturbation. Soil total phosphorus was significantly greater in the 0- and 0.5-year stages than the 5-, 8-, and 14-year stages (p<0.05). Although there were no significant differences in SOM, TOC, and TKN levels before and after timber harvest or between early and mature successional stages, there were consistent trends that may prove beneficial in determining reference standards. A Soil Perturbation Index was developed by combining all four parameters for soils collected in the Chowan River watershed to determine extent of deviation from the biogeochemical reference. Using the model developed in this study, biogeochemical functions decrease after harvesting, with the low point reached at approximately 8 to 9 years after human alteration. This index predicts that it would take 16–17 years for SOM, TOC, TKN, and TP to return to pre-harvest conditions. Perturbation indices could be used for assessment of human impacts, restoration projects, and mitigation of wetlands. We maintain that a Soil Perturbation Index can be one useful component of an index of biotic integrity for wetland ecosystems.

Simulation of the propagation of an acoustic wave through a turbulent velocity field: A study of phase variance

A numerical technique for simulating the behavior of an acoustic wave propagating through a turbulent medium is introduced. The technique involves two elements: the generation of 3-D, random, hypothetical, isotropic velocity fields in terms of a collection of discrete Fourier velocity modes; and the integration of the ray-trace equations to describe the trajectories of points tagging an acoustic wave front. The propagation times for these points to travel fixed distances through each of an ensemble of random velocity fields are recorded, and the variance of travel time (or acoustic phase) over the ensemble is calculated. In numerical ray-trace experiments through fields having average perturbation indices ≊0.01, acoustic travel-time variances are obtained that have a higher-order dependence on travel distance R than the classical Chernov prediction—a linear increase with R. The Chernov result is obtained, however, when the rays are confined to axial trajectories. Additional numerical experiments integrating the stochastic Helmholtz equation and its parabolic approximation yield time-variance estimates consistent with the ray-trace results. Predictions from these simulations are then applied to the laboratory experiments of Blanc-Benon and found to be in qualitative agreement. Finally, a set of 2-D travel-time experiments are presented to identify differences between source–receiver eigenray propagation and preassigned initial direction ray propagation.

A comparison of intrasubject variation across sessions of three vocal frequency perturbation indices.

Within-subject variation of three vocal frequency perturbation indices was compared across multiple sessions. The magnitude of jitter factor (JF), pitch perturbation quotient (PPQ), and directional perturbation quotient (DPF) was measured every other day for 33 consecutive days for ten female and five male normal young adult speakers. Perturbation measures were calculated using a zero-crossing analysis of taped [i] and [u] productions. Pearson product-moment correlations among the three perturbation indices were calculated to examine their relation over time. Coefficients of variation for JF, PPQ, and DPF were considered indicative of the temporal stability of the three measures. JF and PPQ provided redundant information about laryngeal behaviors in steady-state productions. DPF, however, appeared to measure different laryngeal behaviors. Also, JF and PPQ varied considerably within individuals across sessions while DPF was the more temporally stable measure. Multiple sampling sessions and measurement of both the magnitude and direction of period differences are advised for future investigations of vocal frequency perturbation.