Quiet Conditions Research Articles

Lombard effect in Algerian Dialect Speech: Investigation of boosting and bypass strategies in narrowband noisy environment

The paper presents the first investigation on the Lombard effect (LE) in the Algerian Dialect (AD) speech. It is devoted to the examination of boosting and bypass strategies in narrowband noisy environments (0.49–6.8 kHz). Speakers who adopt the boosting tactic would attempt to improve their audibility in noise by increasing the global intensity (I), the local intensity, and the duration (D) of their speech. The boost of the local intensity consists in amplifying the spectral magnitude of the speech waveform in the frequency region wherein the masking noise is beyond 55 dB. However, speakers who apply the bypass strategy would raise their speech in noise so that their fundamental frequency (F0) and first Formant (F1) will decrease. We built the AD Lombard Speech Corpus (ADLSC) that consists of continuous speech files uttered by eight native speakers in quiet and noisy conditions. The corpus contains phonetically rich words that cover all AD phonemes. To examine these strategies, we assessed the change in I, D, F0 and F1 from quiet to noisy environments. Subsequently, we evaluated the change in the local intensity via the computation of the Power Spectrum Ratio (PSR). Statistical tests were conducted to confirm the significance of the acoustic analysis. We found out that speakers raised their vocal effort in I and D. Furthermore, the measured PSRs confirmed the evidence that LE is frequency-specific in humans. Similarly, we noticed that speakers increased their F0 and F1 in noisy conditions. The results we obtained confirmed the boosting strategy but denied the bypass tactic. We compared our findings with the results reported in the state-of-the-art studies. The comparison revealed that LE in narrowband does not exhibit the same acoustic variations in AD and English.

Electron-to-ion Bulk Speed Ratio as a Parameter Reflecting the Occurrence of Strong Electron-dominated Current Sheets in the Solar Wind

Current sheets (CSs) are preferred sites of magnetic reconnection and energy dissipation in astrophysical plasmas. Electric currents in them may be carried by both electrons and ions. In our prior theoretical studies of the CS formation in turbulent plasmas, we utilized fully kinetic and hybrid code simulations with ions considered as particles and electrons—as a massless fluid. We found that electron-dominated CSs in which electrons become the main carriers of the electric current and contributors to energy dissipation may form inside or nearby ion-dominated CSs. These structures represent a distinguished type of CSs and should not be mixed up with so-called electron-scale CSs. Current simulations show that such CSs are characterized by the electron-to-ion bulk speed ratio (u e /u i ) increases that can be seen at ion scales according to theoretical predictions and high-resolution observations from the Magnetospheric Multiscale mission. Therefore, applying the u e /u i parameter to the solar wind data may allow locating the strongest electron-dominated CSs with an ordinary spacecraft resolution of 1−3 s. This study shows that, indeed, electron-dominated CSs observed during a period of quiet solar wind conditions at 1 au impact the surrounding plasma, which may be reflected in sharp changes of u e /u i . Electron-dominated CSs are found to be localized in the vicinity of ion-dominated CSs identified via changes in the magnetic field and plasma parameters, displaying the same clustering. We conclude that u e /u i may be used as one of the key parameters for statistical studies of CSs in the solar wind and analyzing the role of electrons in them.

Model evaluation of accuracy of obtaining total electron content by the method of spaced reception of low Earth orbit satellite signals

A model-based technique to estimate the accuracy of the ionospheric total electron content (TEC) based on the data from spaced receivers of low Earth orbit satellite signals has been suggested. That allows us to estimate the total electron content errors for both quiet ionosphere conditions and under the presence of a plasma ring. To estimate the error, the dynamic model of the electron concentration of the Earth's ionosphere has been used. For the selected input parameters (day of the year, time of day, etc.), a model two-dimensional electron density distribution has been calculated using this model. When calculating this two-dimensional distribution of the electron density, changes have been made that transformed it into a distribution that most closely matches the real ionosphere, for example, the presence of a plasma ring, a trough, etc. Using the obtained distribution, some model quantities (differential phase and total electron content) have been calculated. Then they are used for model estimation of errors in the calculation of the TEC by the spaced reception method. For quite conditions in the ionosphere, the relative error of determining the initial phase constant does not exceed 3 %, and in the case of the plasma ring - 13 %. For the vertical total electron content, the relative error in quite conditions does not exceed 7 %, and in the case of a plasma ring - 60 %. Large values of the relative error are in areas of sharp change of the vertical total electron content.

Positioning performance of the Neustrelitz total electron content model driven by Galileo Az coefficients

To aid single-frequency GNSS users, the Neustrelitz Total Electron Content Model (NTCM) has been proposed as an adequate solution to mitigate propagation errors besides the GPS Klobuchar and Galileo NeQuick models. Using the three effective ionization coefficients broadcast in the Galileo navigation message as driver parameters, the version NTCM-GlAzpar, in general, performs equal to or better than NeQuickG when compared to the total electron content domain. In this work, we performed a global statistical validation of the NTCM-GlAzpar model in the position domain by comparing its results with the results of the Klobuchar and NeQuickG models for the first time. For this purpose, we used the GNSS analysis tool gLAB and its customization capabilities in the Standard Point Positioning mode. The data used for model validation correspond to a one-month period of perturbed solar and geomagnetic activity (December 2014) and another one-month period of quiet conditions (December 2019). The data have a worldwide coverage with up to 73 IGS stations. The statistical analysis of the hourly average 3D position error shows that the root mean squared (RMS) values of the Klobuchar model are 6.71 and 2.75 m for the perturbed and quiet conditions, respectively, whereas the NeQuickG model has RMS values of 4.61 and 2.35 m. In comparison, the corresponding RMS values of 4.36 and 2.32 m of the NTCM-GlAzpar model confirm its better positioning performance for both periods. However, we identify also that the performance of NTCM-GlAzpar slightly worsens toward higher latitudes and at night local time. Simple software adaptations and a low computational cost make NTCM-GlAzpar an alternative practicable algorithm to improve the accuracy of GNSS single-frequency applications.

Electrochemical Oxygen Generator With 99.9% Oxygen Purity and High Energy Efficiency

AbstractUnder the growing crisis of the coronavirus disease 2019 pandemic, the global medical system is facing the predicament of an acute shortage of medical‐grade oxygen (O2, ≥ 99.5% purity). Herein, an oxygen generation device is manufactured that relies on electrochemical technology. The performance of the electrochemical oxygen generator (EOG) is remarkably improved to a practically applicable level, achieving long‐term (>200 h), stable, and quick production (>1.5 L min−1) of high purity O2 (99.9%) at high energy efficiency (496 L kW−1 h−1), via simultaneous optimization for intrinsic electrochemical reaction mechanisms, electrocatalysts, and external cell structure. The EOG also presents powerful competitiveness in user experience, which finds expression in high portability (4.7 kg), nearly instant O2 production (<1 s), and a quiet working condition (<39 dB). The EOG shows great potential to substitute commercial pressure swing adsorption O2 generation devices, which may significantly impact the traditional oxygen production industry.

Loudness affects motion: asymmetric volume of auditory feedback results in asymmetric gait in healthy young adults

BackgroundThe potential of auditory feedback for motor learning in the rehabilitation of various diseases has become apparent in recent years. However, since the volume of auditory feedback has played a minor role so far and its influence has hardly been considered, we investigate the volume effect of auditory feedback on gait pattern and gait direction and its interaction with pitch.MethodsThirty-two healthy young participants were randomly divided into two groups: Group 1 (n = 16) received a high pitch (150-250 Hz) auditory feedback; group 2 (n = 16) received a lower pitch (95-112 Hz) auditory feedback. The feedback consisted of a real-time sonification of the right and left foot ground contact. After an initial condition (no auditory feedback and full vision), both groups realized a 30-minute habituation period followed by a 30-minute asymmetry period. At any condition, the participants were asked to walk blindfolded and with auditory feedback towards a target at 15 m distance and were stopped 5 m before the target. Three different volume conditions were applied in random order during the habituation period: loud, normal, and quiet. In the subsequent asymmetry period, the three volume conditions baseline, right quiet and left quiet were applied in random order.ResultsIn the habituation phase, the step width from the loud to the quiet condition showed a significant interaction of volume*pitch with a decrease at high pitch (group 1) and an increase at lower pitch (group 2) (group 1: loud 1.02 ± 0.310, quiet 0.98 ± 0.301; group 2: loud 0.95 ± 0.229, quiet 1.11 ± 0.298). In the asymmetry period, a significantly increased ground contact time on the side with reduced volume could be found (right quiet: left foot 0.988 ± 0.033, right foot 1.003 ± 0.040, left quiet: left foot 1.004 ± 0.036, right foot 1.002 ± 0.033).ConclusionsOur results suggest that modifying the volume of auditory feedback can be an effective way to improve gait symmetry. This could facilitate gait therapy and rehabilitation of hemiparetic and arthroplasty patients, in particular if gait improvement based on verbal corrections and conscious motor control is limited.

Keratin/Polylactic acid/graphene oxide composite nanofibers for drug delivery

In this work keratin/poly(lactic acid) (PLA) 50/50 wt blend nanofibers with different loadings of graphene-oxide (GO) were prepared by electrospinning and tested as delivery systems of Rhodamine Blue (RhB), selected as a model of a drug. The effect of GO on the electrospinnability and drug release mechanism and kinetics was investigated. Rheological measurements carried out on the blend solutions revealed unsatisfactory compatibility between keratin and PLA under quiet condition. Accordingly, poor interfacial adhesion between the two phases was observed by SEM analysis of a film prepared by solution casting. On the contrary, keratin chains seem to rearrange under the flux conditions of the electrospinning process thus promoting better interfacial interactions between the two polymers, thereby enhancing their miscibility, which resulted in homogeneous and defect-free nanofibers. The loading of GO into the keratin/PLA solution contributes to increase its viscosity, its shear thinning behavior, and its conductivity. Accordingly, thinner and more homogeneous nanofibers resulted from solutions with a relatively high conductivity coupled with a pronounced shear thinning behavior.FTIR and DSC analyses have underlined, that while the PLA/GO interfacial interactions significantly compete with the PLA/keratin ones, there are no significant effects of GO on the structural organization of keratin in blend with the PLA. However, GO offers several advantages from the application point of view by slightly improving the mechanical properties of the electrospun mats and by slowing down the release of the model drug through the reduction of the matrix swelling.

Assessment of Polar Ionospheric Observations by VIPIR/Dynasonde at Jang Bogo Station, Antarctica: Part 1—Ionospheric Densities

Vertical incidence pulsed ionospheric radar (VIPIR) has been operated to observe the polar ionosphere with Dynasonde analysis software at Jang Bogo Station (JBS), Antarctica, since 2017. The JBS-VIPIR-Dynasonde (JVD) provides ionospheric parameters such as the height profile of electron density with NmF2 and hmF2, the ion drift, and the ionospheric tilt in the bottomside ionosphere. The JBS (74.6°S, 164.2°E) is located in the polar cap, cusp, or auroral region depending on the geomagnetic activity and local time. In the present study, an initial assessment of JVD ionospheric densities is attempted by the comparison with GPS TEC measurements which are simultaneously obtained from the GPS receiver at JBS during the solar minimum period from 2017 to 2019. It is found that the JVD NmF2 and bottomside TEC (bTEC) show a generally good correlation with GPS TEC for geomagnetically quiet conditions. However, the bTEC seems to be less correlated with the GPS TEC with slightly larger spreads especially during the daytime and in summer, which seems to be associated with the characteristics of the polar ionosphere such as energetic particle precipitations and large density irregularities. It is also found that the Dynasonde analysis seems to show some limitations to handle these characteristics of the polar ionosphere and needs to be improved to produce more accurate ionospheric density profiles especially during disturbed conditions.

Semantics-Prosody Stroop Effect on English Emotion Word Processing in Chinese College Students With Trait Depression.

This study explored the performance of Chinese college students with different severity of trait depression to process English emotional speech under a complete semantics–prosody Stroop effect paradigm in quiet and noisy conditions. A total of 24 college students with high-trait depression and 24 students with low-trait depression participated in this study. They were required to selectively attend to either the prosodic emotion (happy, sad) or semantic valence (positive and negative) of the English words they heard and then respond quickly. Both prosody task and semantic task were performed in quiet and noisy listening conditions. Results showed that the high-trait group reacted slower than the low-trait group in the prosody task due to their bluntness and insensitivity toward emotional processing. Besides, both groups reacted faster under the consistent situation, showing a clear congruency-induced facilitation effect and the wide existence of the Stroop effect in both tasks. Only the Stroop effect played a bigger role during emotional prosody identification in quiet condition, and the noise eliminated such an effect. For the sake of experimental design, both groups spent less time on the prosody task than the semantic task regardless of consistency in all listening conditions, indicating the friendliness of basic emotion identification and the difficulty for second language learners in face of semantic judgment. These findings suggest the unneglectable effects of college students’ mood conditions and noise outside on emotion word processing.

High-frequency audiometry, speech perception in quiet and noise, and vestibular-evoked myogenic potential in women with polycystic ovary syndrome

PurposeThe study aimed to investigate the effect of PCOS on high-frequency thresholds, speech perception in quiet and in presence of noise, and vestibular functioning in women with and without PCOS and to correlate the speech perception scores with that of the pure-tone thresholds obtained at conventional and higher frequencies.MethodsWomen with and without PCOS in the age range of 18–40 years diagnosed between January 2019 and January 2020 were participants. Conventional and high-frequency audiometry (HFA), speech perception in quiet and in noise (SPIN), and cervical vestibular-evoked myogenic potentials (cVEMP) and ocular vestibular-evoked myogenic potentials (oVEMP) were assessed for both groups.ResultsConventional audiometry (250 Hz to 8000 Hz) showed no statistically significant difference between both groups. High-frequency audiometry (9000 Hz to 20,000 Hz) showed significantly poorer pure-tone thresholds for women with PCOS compared to women without PCOS. SPIN results showed significantly lower SPIN scores for women with PCOS for − 3dB SNR, − 6 dB SNR, and − 9dB SNR. No difference in scores was observed for quiet conditions and 0 dB SNR for women with and without PCOS. cVEMP and oVEMP responses showed reduced amplitude in women with PCOS.ConclusionAll the women diagnosed with having PCOS should be screened for hearing loss, speech perception difficulty in quiet and in presence of noise, and vestibular system functioning. If the hearing is affected, intervention should be started early in life.

Ionospheric disturbance statistics according to the Swarm satellite mission in 2014

In the present work, based on the database of magnetic field indices Kp, AE, and Dst, we consider the relationship between geomagnetic activity and ionospheric scintillation indices S4 and RODI based on in-situ satellite measurements. 37 events with quiet and disturbed geomagnetic conditions during 2014 were selected and analyzed. The correlation coefficients of the scintillation indices with high-latitude AE and low-latitude Dst are obtained. Thus, in periods of disturbed geomagnetic conditions, the RODI10s and S4 indices are, in principle, equally related to the high-latitude AE index (with a small, up to 4% in the number of realizations, the advantage of the RODI index) In periods with quiet geomagnetic conditions, the situation changes - in 17% of cases the S4 index is better reflects a relationship with mid-latitude Dst than the RODI10s index. The indicated relationship means the presence of a linear correlation of more than 0.3 between the processes.

Using the bispectrum to probe radio X-ray correlations in GRS 1915+105

ABSTRACT We present the results of bicoherence analysis on observations of GRS 1915+105 that exhibit quasi-periodic oscillations (QPOs). The bicoherence is a higher order statistic that can be used to probe the relation between the phases of a triplet of Fourier frequencies. Despite showing very similar power spectra, the observations exhibit different patterns in their bicoherence, indicating that the QPOs are phase coupled to the noise in different ways. We show that the bicoherence pattern exhibited correlates with the frequency of the QPO, the hardness ratio, as well as the radio properties of the source. In particular, we find that the nature of phase coupling between the QPO and the high and low frequency broad-band components is different between radio quiet, radio plateau, and radio steep conditions. We also investigate the phase lag behaviour of observations with QPO frequency above 2 Hz that show different bicoherence patterns and find statistically significant differences between them, indicating a change in the underlying physical mechanism. Finally, we present a scenario whereby the cooling of the jet electrons by soft photons from the accretion disc could explain the observed correlations between the bicoherence and radio properties.

Ionospheric Nighttime F‐Region Irregularities During Geomagnetically Quiet Conditions as Observed With 205 MHz VHF Radar at an Equatorial Trough Station, Cochin

AbstractThe VHF radar operating at 205 MHz frequency installed at the Cochin University of Science and Technology (CUSAT) has been configured to probe the nighttime ionospheric field‐aligned irregularities (FAIs) over the near‐equatorial site at Cochin, India during the solar minimum periods. Even though the study period includes the minimum of the 24th and 25th solar cycles, a total of 40 nighttime irregularity events were observed at F‐region heights (150–500 km). Bottom‐type and bottom‐side irregularities were observed in this period, but no large‐scale topside ones at F‐region heights. The nighttime irregularities were most commonly observed at average heights of 200–250 km, accounting for 50% of the total events, and 27.5% of the irregularities preferentially occurred after sunset between 19 and 20 LT. While long‐duration irregularity events were not prominent during this period, irregularities that lasted for less than 50 min were predominant. To check the capability of the 205 MHz VHF radar in observing FAIs, the radar observations were compared with the European Space Agency's ionospheric observation data from the Swarm B satellite. Several derived parameters from the Swarm data set such as electron density (Ne), background Ne (bNe), electron temperature (Te), rate of electron density (ROD), index of ROD (RODI), median vertical total electron content (mVTEC), absolute VTEC (aVTEC), rate of TEC (ROT), ROTI, Bubble Index, and Bubble Probability were utilized for characterizing the ionospheric irregularities. The observation from the Swarm B satellite agrees well with that obtained from the VHF radar.

Magnetic stimulation allows focal activation of the mouse cochlea.

Cochlear implants (CIs) provide sound and speech sensations for patients with severe to profound hearing loss by electrically stimulating the auditory nerve. While most CI users achieve some degree of open set word recognition under quiet conditions, hearing that utilizes complex neural coding (e.g., appreciating music) has proved elusive, probably because of the inability of CIs to create narrow regions of spectral activation. Several novel approaches have recently shown promise for improving spatial selectivity, but substantial design differences from conventional CIs will necessitate much additional safety and efficacy testing before clinical viability is established. Outside the cochlea, magnetic stimulation from small coils (micro-coils) has been shown to confine activation more narrowly than that from conventional microelectrodes, raising the possibility that coil-based stimulation of the cochlea could improve the spectral resolution of CIs. To explore this, we delivered magnetic stimulation from micro-coils to multiple locations of the cochlea and measured the spread of activation utilizing a multielectrode array inserted into the inferior colliculus; responses to magnetic stimulation were compared to analogous experiments with conventional microelectrodes as well as to responses when presenting auditory monotones. Encouragingly, the extent of activation with micro-coils was ~60% narrower compared to electric stimulation and largely similar to the spread arising from acoustic stimulation. The dynamic range of coils was more than three times larger than that of electrodes, further supporting a smaller spread of activation. While much additional testing is required, these results support the notion that magnetic micro-coil CIs can produce a larger number of independent spectral channels and may therefore improve auditory outcomes. Further, because coil-based devices are structurally similar to existing CIs, fewer impediments to clinical translational are likely to arise.

Detailed analysis of the behavior of the F2-layer critical frequency prior to geomagnetic storms

A detailed analysis of the dependence of the number of events (critical frequency foF2 deviations on prestorm days from quiet conditions) and their intensity on the intensity of the coming magnetic storm and solar activity is performed. In order to separate the effects of the dependence on different parameters, the dependence on solar activity is considered for narrow intervals of Dst, (the measure of the storm intensity), whereas the dependence on the storm intensity is considered for narrow intervals of the F10.7 index characterizing solar activity. The conclusions on the decrease of the aforementioned numbers under an increase in the negative value of Dst (intensification of the storm) and F10.7 (solar activity increase) are confirmed. In is found that an increase in the event intensity is observed at intensification of the storm and that the intensity decreases at an increase in F10.7. The results of the analysis separately for each prestorm day shows that both the number of the events and their intensity are decreasing with remoting from the storm beginning (a transition from the zero days to other days).

Unexpected Regional Zonal Structures in Low Latitude Ionosphere Call for a High Longitudinal Resolution of the Global Ionospheric Maps

This study reports unexpected strong longitudinal structures from Global Navigation Satellite System (GNSS) derived total electron content (TEC) observations in the low-latitude ionosphere over Asia. The observations during 2019–2020 show diverse patterns in the zonal difference of regional TEC, even under geomagnetically quiet conditions. The TEC in the northern hemisphere occasionally exhibits drastic zonal gradients. The intense regional gradients in TEC span a longitudinal extent of about 20°. The higher values may appear on the east or the west side. Strong zonal gradients may appear in all seasons, regardless of geomagnetically quiet or active conditions. The 15 December 2019 and 16 March 2020 cases depict an intense zonal differences cluster in the narrow latitudinal band of 16°N to 28°N, spanning a regional scale smaller than the normal longitudinal structures. In contrast, the Global Ionospheric Maps (GIMs) with a longitudinal resolution of 5° show a much flatter zonal picture. Such intense and regional-scale zonal structures in the low-latitude ionosphere call for a high zonal resolution of GIMs in terms of better geographically distributed observations. Notably, no counterpart regional structures are found at the conjugated points in the southern hemisphere during the two cases. Although the physical drivers are not certain, the appearance only in the northern hemisphere possibly excludes the dominant contribution to forming the regional structures from the equatorial electric field.

Multi-Station and Multi-Instrument Observations of F-Region Irregularities in the Taiwan–Philippines Sector

In this study, a multi-station and multi-instrument system, organized and proposed for ionospheric scintillation and equatorial spread-F (ESF) specification and their associated motions in the Taiwan–Philippines sector, is outlined. The issues related to the scintillation and ESF event observed on 26 October 2021, at magnetic quiet conditions are presented and discussed. We first indicate the existence of a plasma bubble in the Taiwan–Philippines sector by using the FormoSat-7/Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (FS7/COSMIC2) GPS/GLONASS radio occultation observations. We verify the latitudinal extent of the tracked plasma bubble using the recorded ionograms from the Vertical Incidence Pulsed Ionospheric Radar located at Hualien, Taiwan. We further discuss the spatial and temporal variabilities of two-dimensional vertical scintillation index VS4 maps based on the simultaneous GPS L1-band signal measurements from 133 ground-based receivers located in Taiwan and the surrounding islands. We also operate two high-sampling, software-defined GPS receivers and characterize the targeted plasma irregularities by carrying out spectrum analyses of the received signal. As a result, the derived plasma irregularities moved eastward and northward. Furthermore, the smaller the irregularity scale, the higher the spectral index and the stronger the scintillation intensity were at lower latitudes on the aimed irregularity feature.

Effects of Noise Exposure and Aging on Behavioral Tone Detection in Quiet and Noise by Mice.

Aging leads to degeneration of the peripheral and central auditory systems, hearing loss, and difficulty understanding sounds in noise. Aging is also associated with changes in susceptibility to or recovery from damaging noise exposures, although the effects of the interaction between acute noise exposure and age on the perception of sounds are not well studied. We tested these effects in the CBA/CaJ mouse model of age-related hearing loss using operant conditioning procedures before and after noise exposure and longitudinally measured changes in their sensitivity for detecting tones in quiet or noise backgrounds. Cochleae from a subset of the behaviorally tested mice were immunolabeled to examine organ of Corti damage relative to what is expected based on aging alone. Mice tested in both quiet and noise background conditions experienced worse behavioral sensitivity immediately after noise exposure, but mice exposed at older ages generally showed greater threshold shifts and reduced recovery over time. Surprisingly, day-to-day stability in thresholds was markedly higher for mice detecting signals in the presence of a noise masker compared with detection in quiet conditions. Cochlear analysis revealed decreases in the total number of outer hair cells (OHCs) and the number of ribbons per inner cell in high-frequency regions in aged, noise-exposed mice relative to aging alone. Our findings build on previous work showing interactions between age and noise exposure and add that background noise can increase the stability of behavioral hearing sensitivity after noise damage.

Effects of type of early reflection, clarity of speech, reverberation and diffuse noise on the spatial perception of a speech source and its intelligibility.

Changing the balance between the early and late reflections in the impulse response affects the clarity of speech, and also the spatial perception of the sound source is affected when the direction of the early reflections is manipulated. While the effect of noise on early reflections has long been investigated in speech intelligibility studies, it is unclear whether and how the spatial characteristics of the source are altered by noise, and whether this would influence speech intelligibility in any way. The aim of the present work was to analyze the spatial perception of a speech source in noise and its relationship, if any, with speech intelligibility. Impulse responses with specular or scattered early reflections and two different reverberant tails were used to create sound fields with controlled clarity and reverberation. It emerged that noise affects spatial cues compared to the reverberation-only (quiet) condition; ratings are consequently changed, and most percepts are distorted. Speech intelligibility is also sensitive to changes in acoustic variables and the type of reflection, but the direct association between spatial percepts and speech intelligibility is weak.

Modelling M(3000)F2 at an African Equatorial Location for Better IRI‐Model Prediction

AbstractThe F2‐layer propagation factor M(3000)F2 is important to ionospheric studies owning to its use in high High frequency radio communication/ionospheric modeling. This study focused on reducing the shortcomings in the use of M(3000)F2 IRI‐model for obtaining hmF2, especially in the African equatorial region, by obtaining an empirical “constructed model” (M(3000)F2CM) using the Korhogo (geomag. lat. 1.26°S, long. 67.38°E, dip. −0.67°S) data (M(3000)F2KOR). The data spans 8 years (1993–2000) under magnetically quiet conditions (Ap < 20 nT). The Regression method technique was used in obtaining the M(3000)F2CM. The regression coefficient (R2) for the M(3000)F2KOR versus F10.7 relationship was stronger during the solstices. The associated diurnal equations obtained for all seasons from the regression plot of the M(3000)F2KOR‐F10.7 relationship were used to obtained the constructed model equation given by M(3000)F2CM(m)i = ai(m) ∗ (F10.7) + bi(m), which allows the prediction of diurnal, seasonal and solar cycle variation of the M(3000)F2 parameter. M(3000)F2CM predicted well when tested at different solar activities. Generally, M(3000)F2CM performed reasonably well in comparison with the IRI model (M(3000)F2IRI) when validated with Ouagadougou (lat. 0.59°S, long. 71.46°E) observed data ‐ M(3000)F2OUA. The percentage deviation of M(3000)F2CM versus M(3000)F2OUA during high solar activity and low solar activity ranges from −10.8–5.3/−7.6–15.8 for solstices/equinoxes; whereas percentage deviation of M(3000)F2IRI versus M(3000)F2OUA spans −15.5–9.2 and −9.7–17.7 in similar order of seasons. The characteristic diurnal post‐sunset drop in M(3000)F2, a prominent feature of the equatorial ionosphere is well captured by the empirical model. These results suggest that the new model has a measure of potential for its use in the equatorial African region.