Apparent Source Research Articles

Sources of water for the outflow channels on Mars: Implications of the Late Noachian “icy highlands” model for melting and groundwater recharge on the Tharsis rise

From the Late Noachian period, through the Hesperian, and into the Amazonian periods on Mars, large outflow channels were formed. Many are interpreted to have originated through the catastrophic discharge of groundwater from martian aquifers, involving the release of up to millions of cubic-kilometers of water. Such a mechanism for outflow channel formation requires that martian aquifers were supplied with significant quantities of water some time prior to the discharge events. Typical groundwater recharge occurs due to the infiltration of surficial waters through a permeable substrate down into aquifers. However, some climate models predict an early martian climate dominated by generally “cold and icy” conditions. In this scenario, a globally continuous, impermeable cryosphere prevents infiltration of liquid water (that might be generated at the surface through anomalous heating conditions), leaving the martian aquifers without an apparent source of recharge to supply later outflow channel formation by groundwater discharge. More recent global climate modeling of an early, thicker CO2 martian atmosphere predicts that, when coupled with a full water cycle, the atmosphere of Mars will behave adiabatically causing temperatures to decrease with elevation. The high standing areas of Mars, such as the southern highlands and the Tharsis region, then act as cold traps. This leads to the preferential accumulation of snow and ice, resulting in the formation of regional ice sheets throughout the highlands that characterize the Late Noachian “icy highlands” early Mars climate model (LNIH). We make the initial assumption that the LNIH model is representative of the early Mars climate, and seek to test the model against the presence of the Hesperian and Amazonian outflow channels to determine if it can be consistent. In order to reconcile the LNIH early Mars climate model with the presence of the later outflow channels a groundwater recharge mechanism that can operate under the predicted “cold and icy” conditions is required. We test basal melting of surface snow and ice in response to a regionally elevated geothermal heat flux throughout the Tharsis rise (resulting from widespread volcanic and magmatic activity during the Noachian) as a mechanism that can provide: (1) liquid water generation at the surface of Mars under generally “cold and icy” conditions, and (2) potentially large scale integration of the hydrological system (through thinning or breaching of the cryosphere), allowing for infiltration of meltwater to provide groundwater recharge during the Late Noachian to supply the later formation of outflow channels. We find: (1) Regional scale basal melting of LNIH ice sheets is not likely to occur at the predicted nominal average ice sheet thicknesses, even in the presence of the anomalous bottom-up heating conditions expected in the Tharsis region (although the increased baseline heating will render the LNIH ice sheets more susceptible to melting through additional anomalous heating conditions introduced by top-down and bottom-up processes). (2) Local scale basal melting and groundwater recharge through a “heat-pipe drain pipe” mechanism is likely to occur, but is not predicted to produce sufficient groundwater recharge to supply the water needed to form the outflow channels. (3) Under the assumption of an ice saturated cryosphere, regional scale melting of the cryosphere due to the insulating effect of the LNIH ice sheets does not provide enough water to explain the formation of all of the outflow channels. Therefore, if the LNIH model is correct, the groundwater recharge that supplied outflow channel formation requires a source that operated earlier in martian history, or the recharge was supplied by other mechanisms.

Autocorrelation-Based Features for Speech Representation

This study investigates autocorrelation-based features as a potential basis for phonetic and syllabic distinctions. The work comes out of a theory of auditory signal processing based on central monaural autocorrelation and binaural crosscorrelation representations. Correlation-based features are used to predict monaural and binaural perceptual attributes that are important for the architectural acoustic design of concert halls: pitch, timbre, loudness, duration, reverberation-related coloration, sound direction, apparent source width, and envelopment (Ando, 1985, 1998; Ando and Cariani, 2009). The current study investigates the use of features of monaural autocorrelation functions (ACFs) for representing phonetic elements (vowels), syllables (CV pairs), and phrases using a small set of temporal factors extracted from the short-term running ACF. These factors include listening level (loudness), zero-lag ACF peak width (spectral tilt), τ1 (voice pitch period), φ1 (voice pitch strength), τe (effective duration of the ACF envelope, temporal repetitive continuity/contrast), segment duration, and Δφ1/Δt (the rate of pitch strength change, related to voice pitch attack-decay dynamics). Times at which ACF effective duration τe is minimal reflect rapid signal pattern changes that usefully demarcate segmental boundaries. Results suggest that vowels, CV syllables, and phrases can be distinguished on the basis of this ACF-derived feature set.

A correlation between hard gamma-ray sources and cosmic voids along the line of sight

We estimate the galaxy density along lines of sight to hard extragalactic gamma-ray sources by correlating source positions on the sky with a void catalog based on the Sloan Digital Sky Survey (SDSS). Extragalactic gamma-ray sources that are detected at very high energy (VHE; E>100 GeV) or have been highlighted as VHE-emitting candidates in the Fermi Large Area Telescope hard source catalog (together referred to as "VHE-like" sources) are distributed along underdense lines of sight at the 2.4 sigma level. There is also a less suggestive correlation for the Fermi hard source population (1.7 sigma). A correlation between 10-500 GeV flux and underdense fraction along the line of sight for VHE-like and Fermi hard sources is found at 2.4 sigma and 2.6 sigma, respectively. The preference for underdense sight lines is not displayed by gamma-ray emitting galaxies within the second Fermi catalog, containing sources detected above 100 MeV, or the SDSS DR7 quasar catalog. We investigate whether this marginal correlation might be a result of lower extragalactic background light (EBL) photon density within the underdense regions and find that, even in the most extreme case of a entirely underdense sight line, the EBL photon density is only 2% less than the nominal EBL density. Translating this into gamma-ray attenuation along the line of sight for a highly attenuated source with opacity tau(E,z) ~5, we estimate that the attentuation of gamma-rays decreases no more than 10%. This decrease, although non-neglible, is unable to account for the apparent hard source correlation with underdense lines of sight.

Multi-state mark-recapture model to estimate survival of a dispersed-nesting seabird, the Kittlitz's Murrelet

The Kittlitz's murrelet (Brachyramphus brevirostris) is a small, dispersed-nesting seabird that often occurs in glacially influenced marine waters of Alaska and eastern Russia during the breeding season. Owing to its association with glacial habitats and apparent population declines in some parts of its range, the Kittlitz's murrelet has been the subject of considerable conservation concern in recent years. We present the first-ever estimates of breeding season and annual survival of the Kittlitz's murrelet. We estimated survival by capturing 914 murrelets and radiotagging 191 of them in Icy Bay, Alaska, 2007–2012. We used a multi-state mark–recapture framework to estimate breeding season survival. Daily survival probabilities were similar in the 3 spatial states (Icy Bay, Gulf of Alaska, nest; range = 0.996–0.999), resulting in an overall 60-day breeding season survival probability of 0.89 (SE = 0.04). The only apparent source of fatality of Kittlitz's murrelets during the breeding season was avian predators, specifically bald eagle (Haliaeetus leucocephalus) and peregrine falcon (Falco peregrinus). We estimated mean apparent annual survival across all years as 0.80 (SE = 0.33) with a recapture probability of 0.079 (SE = 0.032), resulting in a 305-day non-breeding season survival probability of 0.90 (SE = 0.37). We found that survival was lower than expected based on life-history theory and allometry, and that fatality risk was greater in the breeding season compared to other parts of the year. Our results indicating low survival rates of Kittlitz's murrelets are consistent with the observed decline of 10% per annum in the local population of this species in Icy Bay. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Acoustic investigation of wall jet over a backward-facing step using a microphone phased array

The acoustic properties of a wall jet over a hard-walled backward-facing step of aspect ratios 6, 3, 2, and 1.5 are studied using a 24-channel microphone phased array at Mach numbers up to M=0.6. The Reynolds number based on inflow velocity and step height assumes values from Reh=3.0×104 to 7.2×105. Flow without and with side walls is considered. The experimental setup is open in the wall-normal direction and the expansion ratio is effectively 1. In case of flow through a duct, symmetry of the flow in the spanwise direction is lost downstream of separation at all but the largest aspect ratio as revealed by oil paint flow visualization. Hydrodynamic scattering of turbulence from the trailing edge of the step contributes significantly to the radiated sound. Reflection of acoustic waves from the bottom plate results in a modulation of power spectral densities. Acoustic source localization has been conducted using a 24-channel microphone phased array. Convective mean-flow effects on the apparent source origin have been assessed by placing a loudspeaker underneath a perforated flat plate and evaluating the displacement of the beamforming peak with inflow Mach number. Two source mechanisms are found near the step. One is due to interaction of the turbulent wall jet with the convex edge of the step. Free-stream turbulence sound is found to be peaked downstream of the step. Presence of the side walls increases free-stream sound. Results of the flow visualization are correlated with acoustic source maps. Trailing-edge sound and free-stream turbulence sound can be discriminated using source localization.

Statistical Survey of Type III Radio Bursts at Long Wavelengths Observed by the Solar TErrestrial RElations Observatory (STEREO)/Waves Instruments: Goniopolarimetric Properties and Radio Source Locations

We have performed statistical analysis of a large number of Type III radio bursts observed by STEREO between May 2007 and February 2013. Only intense, simple, and isolated cases have been included in our data set. We have focused on the goniopolarimetric (GP, also referred to as direction-finding) properties at frequencies between $125$ kHz and $2$ MHz. The apparent source size $\gamma$ is very extended ($\approx60^\circ$) for the lowest analyzed frequencies. Observed apparent source sizes $\gamma$ expand linearly with a radial distance from the Sun at frequencies below $1$ MHz. We have shown that Type III radio bursts statistically propagate in the ecliptic plane. Calculated positions of radio sources suggest that scattering of the primary beam pattern plays an important role in the propagation of Type III radio bursts in the IP medium.

Internal processes within the African Easterly Wave system

The internal processes within an African Easterly Wave (AEW) system, involving mass, dynamic and water vapour fields are investigated using ERA‐I reanalysis, in order to highlight the interactions between convection and AEWs. The budgets of heat, moisture and momentum are analysed during the different phases of AEWs detected using synoptic‐scale precipitable water anomalies as proposed by Poan et al. (2013). The strong climatological meridional gradient of moisture present in the Sahel impacts the shape of the apparent heat source and humidity sink. AEW events over the Sahel are associated with a meridional shift of the intertropical convergence zone (ITCZ). Large exchanges of momentum by small‐scale convective transport are also highlighted between the low‐ and mid‐levels, contributing to the reinforcement of the AEW circulation at 600 hPa and the damping of the monsoon flow. This also appears as a possible mechanism for the vertical tilt of the meridional wind associated with AEWs. Heat budget computation, in the southern flank of the West African Heat‐Low (HL) region where such AEWs occur, reveals that the heating anomalies are mainly driven by the horizontal advections. The vertical circulation acts as a precursor, which initiates the heat transport in the lower troposphere. However, weaker, turbulent mixing also participates in the development of these anomalies, especially in the boundary layer. These budgets ultimately allow the distinct contributions of diabatic and adiabatic processes to be determined.

Analysis and observation of spacecraft plume/ionosphere interactions during maneuvers of the space shuttle

AbstractThis work employs in situ measurement data and constructive simulations to examine the underlying physical mechanisms that drive spacecraft plume interactions with the space environment in low‐Earth orbit. The study centers on observations of the enhanced flux of plasma generated during a maneuver of Space Shuttle Endeavour as part of the Sensor Test for Orion Relative Navigation Risk Mitigation experiment in May 2011. The Canary electrostatic analyzer (ESA) instrument mounted on the portside truss of the International Space Station indicated an elevated ion current during the shuttle maneuver. The apparent source of enhanced ion current is a result of interaction of the spacecraft thruster plume with the rarefied ambient ionosphere, which generates regions of relatively high density plasma through charge exchange between the neutral plume and ambient ions. To reconstruct this event, unsteady simulation data were generated using a combined direct simulation Monte Carlo/particle‐in‐cell methodology, which employed detailed charge exchange cross‐section data and a magnetic field model. The simulation provides local plasma characteristics at the ESA sensor location, and a sensor model is subsequently used to transform the local properties into a prediction of measured ion current. The predicted and observed total currents are presented as a function of time over a 30 s period of pulsed thruster firings. A strong correlation is observed in the temporal characteristics of the simulated and measured total current, and good agreement is also achieved in the total current predicted by the model. These results support conclusions that (1) the enhanced flux of plasma observed by the ESA instrument is associated with Space Shuttle thruster firings and (2) the simulation model captures the essential features of the plume interactions based on the observation data.

Grandes expectativas: la democracia mexicana y sus descontentos

There is no doubt that democracy in México has fallen short of expectations: it has not increased social and economic equality. Few people deem their participation in politics is now more effective than before, the elected government often fails to meet citizens' demands, and some regions of the country are seemingly under the control of violent drug cartels. These faults certainly fuel the voters' discontent with the democratic regime. The aim of this paper though is to focus on other less apparent sources of the existing intense political dissatisfaction. Mexicans are unsatisfied with their democratic government not only because it has not provided them with the social goods they are realistically or not expecting from democracy. They are also unhappy due to the perceived gap between an idealized notion of democracy and the way the existing democratic institutions actually work, as an odd ahistorical image of democracy has been constructed. The major claim of this work is that the critical standard of democracy assumed by Mexicans is inaccurate. It will be argued that this ideological misconception has had pernicious effects, as it has nurtured unreasonable expectations and has inhibited Mexicans from considering feasible reforms. It will be also examined in particular the role played by the pursuit of equity.

Development of egg-configuration heat source model in numerical simulation of autogenous fusion welding process

The mathematical structure of the heat source models should at least approximately represent the phenomena of real heat source. In fusion welding process, only the surface heat flux fails to realize enhanced heat transfer due to predominant effect of momentum transport of the material within molten pool. The convection in the weld pool can be substituted by apparent volumetric heat source which is unrealistic to define outside the molten pool volume. The key issues to define a decent volumetric heat source are the geometric shape and size, non-symmetric heat density distribution due to moving arc or laser beam. In present work, the egg-configuration volumetric heat source model is proposed to address these issues. The proposed heat source model which is derived from ellipsoid shape provides the non-symmetry heat energy distribution with less number of model parameters and conserves the continuity in profile during moving heat source problem. The general equation of egg-configuration heat source provides the basis of Gaussian distributed disc, hemispherical, and semi-ellipsoidal volumetric heat source models which can be considered as the special cases of proposed heat source model. A 3D finite element based transient heat transfer analyses is conducted using the proposed heat source model for gas tungsten arc welding (GTAW) and diode laser welding processes. The maximum deviation of 10% in weld pool size estimation is observed as compared to experimental results. The time-temperature history confirms the peak temperatures of 940 K and 1060 K, respectively for GTAW and laser welding processes. The amount of the maximum cooling rate predicted for GTAW is 603 K/s which is significantly lower than 11.1 × 103 K/s for laser welding. Overall, the proposed heat source model generalized the applicability over a wide variety of materials and autogenous fusion welding processes.

An overview of dissolved Fe and Mn distributions during the 2010–2011 U.S. GEOTRACES north Atlantic cruises: GEOTRACES GA03

High-resolution dissolved Fe (dFe) and dissolved Mn (dMn) distributions were obtained using a trace metal clean rosette during the GEOTRACES GA03 zonal transect cruises (USGT10 and USGT11) across the North Atlantic Ocean. This manuscript provides a general overview of the dFe, as well as dMn and dissolved Al (dAl) distributions that reveal several Fe inputs at varying depths across the study region. Elevated dFe concentrations correlate with elevated dAl concentrations in the surface waters of the subtropical gyre, indicating a significant atmospheric source of Fe, in contrast there is no apparent significant dust source for Mn. In the subsurface waters, dFe maxima are a result of the remineralization process, as revealed by their correspondence with dissolved oxygen minima. Within the oxygen minimum, the ratio of dFe to apparent oxygen utilization (AOU) is lower than would be expected from the measured Fe content of surface water phytoplankton, suggesting that a significant amount of dFe that is remineralized at depth (~63–90%) is subsequently scavenged from the water column. The rate of remineralization, which is based on the slope of dFe:AOU plot, is similar across a wide area of the North Atlantic. In addition to the remineralization process, sedimentary inputs are apparent from elevated dMn signals in the eastern basin, particularly near the African coast. In the western basin, sedimentary input is also occurring along the advective flow path of the Upper Labrador Sea Water (ULSW), as ULSW transits along the North American continental shelf region. The largest dFe anomaly (~68nM), which also corresponds to a dMn anomaly (up to ~33nM) is seen in the neutrally buoyant hydrothermal plume sampled over the Mid-Atlantic Ridge, and that signal is visible for ~500km to the west of the ridge.

Three-dimensional volcano-acoustic source localization at Karymsky Volcano, Kamchatka, Russia

We test two methods of 3-D acoustic source localization on volcanic explosions and small-scale jetting events at Karymsky Volcano, Kamchatka, Russia. Recent infrasound studies have provided evidence that volcanic jets produce low-frequency aerodynamic sound (jet noise) similar to that from man-made jet engines. For man-made jet noise, noise sources localize along the turbulent jet flow downstream of the nozzle. Discrimination of jet noise sources along the axis of a volcanic jet requires high resolution in the vertical dimension, which is very difficult to achieve with typical volcano-acoustic network geometries. At Karymsky Volcano, an eroded edifice (Dvor Caldera) adjacent to the active cone provided a platform for the deployment of five infrasound sensors in July 2012 with intra-network relief of ~600m. The network was designed to target large-scale jetting, but unfortunately only small-scale jetting and explosions were recorded during the 12-day experiment. A novel 3-D inverse localization method, srcLoc, is tested and compared against a more common grid-search semblance technique. Simulations using synthetic signals show that srcLoc is capable of determining vertical solutions to within ±150m or better (for signal-to-noise ratios ≥1) for this network configuration. However, srcLoc locations for explosions and small-scale jetting at Karymsky Volcano show a persistent overestimation of source elevation and underestimation of sound speed. The semblance method provides more realistic source locations, likely because it uses a fixed, realistic sound speed of ~340m/s. Explosion waveforms exhibit amplitude relationships and waveform distortion strikingly similar to those theorized by modeling studies of wave diffraction around the crater rim. We suggest that the delay of acoustic signals and apparent elevated source locations are due to raypaths altered by topography and/or crater diffraction effects, implying that topography in the vent region must be accounted for when attempting 3-D volcano acoustic source localization. Though the data presented here are insufficient to resolve small-scale jet noise sources, similar techniques may be successfully applied to large volcanic jets in the future.

The gravimetric picture of magmatic and hydrothermal sources driving hybrid unrest on Tenerife in 2004/5

We present results from the inversion of gravity changes observed at the central volcanic complex (CVC) of Tenerife, Canary Islands, between May 2004 and July 2005. Marking a period of elevated activity and a reawakening of the volcanic system, the data depict spatial and temporal variations in the sub-surface processes that defined this period of unrest at the Pico Viejo (PV)–Pico Teide (PT) complex, after the last volcanic eruption on Tenerife in 1909. An initial non-linear inversion, based on 3D line segments approximation, yielded three line segments at depths between 1kma.s.l. and 2km b.s.l. Our interpretation of the initial inversion results is that the line segments represent apparent composite sources, a superposition of deep and shallow seated sources. We therefore decomposed the gravity changes into shallow and deep parts (fields) using a procedure based on triple harmonic continuation. The shallow and deep fields could then be inverted separately, using the same inversion methodology. The deep field constrains two connected line segments at the depth of about 6km b.s.l., in the center of the NW seismogenic zone of VT event swarm of the seismic unrest, that we interpret as magma input. The inversion of the shallow field images three weak line segments that are all situated at very shallow, near-surface depths. We interpret the weak segments as hydrothermal sources potentially excited by the deeper magma injection. Our results indicate no significant input into the shallow phonolitic plumbing system of the PV–PT complex, but rather a deeper-seated rejuvenation of the mafic feeder reservoir. The emerging picture from our analysis is that the 2004/5 unrest on Tenerife was of a hybrid nature due to the combination of a deep magma injection (failed eruption?) coupled with fluid migration to shallow depths. The identified causative link between deep and shallow unrest sources indicates the presence of permeable pathways for shallow fluid migration at the CVC.

The perception of apparent auditory source width in hearing-impaired adults

In a previous study [Whitmer, Seeber and Akeroyd, J. Acoust. Soc. Am. 132, 369-379 (2012)], it was demonstrated that older hearing-impaired (HI) listeners produced visual sketches of headphone-presented noises that were insensitive to changes in interaural coherence. The current study further explores this insensitivity by comparing (a) binaural temporal fine-structure (TFS) resolution and (b) sound localization precision to (c) auditory source width judgments. Thirty-five participants aged 26-81 years with normal to moderately impaired hearing (a) discriminated interaurally phase-shifted tones from diotic tones presented over headphones, (b) located 500-ms speech-spectrum filtered click trains presented over loudspeakers between ±30° in quiet, and (c) sketched the perceived width of low-pass, high-pass, and speech-spectrum noise stimuli presented over loudspeakers from 0° and simultaneously from ±45° at attenuations of 0-20 dB to generate partially coherent stimuli. The results showed a decreasing sensitivity to width with age and impairment which was related to binaural TFS threshold: the worse one's threshold-which was correlated with age-the less the perceived width increased with decreasing interaural coherence. These results suggest that senescent changes to the auditory system do not necessarily lead to perceptions of broader, more diffuse sound images based on interaural coherence.

Equivalent Point-Source Modeling of Moderate-to-Large Magnitude Earthquakes and Associated Ground-Motion Saturation Effects

We modeled the source and attenuation attributes of well-recorded M6� earthquakes based on the equivalent point-source approach, with the goal of determin- ing how to treat ground-motion saturation effects within this context. We consider ground motions as originating from an equivalent point source and mimic finite-fault effects by treating the motion as emanating from a virtual point (not a real point on the fault rupture), such that ground motions are correctly predicted at close distances. This is achieved by using an effective distance metric R �� D 2 � h 2 � 0:5 , in which Drup is the closest distance to the rupture and h is a pseudodepth term that accounts for sat- uration effects. We found that the distance-saturation effect is magnitude dependent, extending to further distances with increasing magnitude. For earthquakes of M ≥6, we model the saturation term as logh �� −1:72 � 0:43 M with a standard deviation of 0.19 in log10 units, based on the values obtained from the study earthquakes. The apparent source spectra of most M6� earthquakes can be modeled using a simple Brune point-source model. For a few of the M6� earthquakes, notably those in California, we observed a spectral sag at intermediate frequencies. For such earth- quakes, a two-corner point-source model provides a better match than the Brune model. We conclude that an equivalent point-source model based on the effective distance concept can successfully predict the average ground motions from M6� earthquakes over a wide distance range, including close distances (<20 km).

Characteristics of the 17 May 2013 M 4.5 Ladysmith, Quebec, Earthquake

ABSTRACT The 17 May 2013 M 4.5 Ladysmith, Quebec, earthquake produced a rich instrumental and felt ground‐motion database. We use instrument‐corrected response spectra and Fourier amplitude data from 189 stations, at distances from 10 to 700 km, to examine the attenuation and source characteristics of this event. An interesting observation is that amplitudes were elevated throughout southern Ontario, probably due to site effects, possibly coupled with source radiation effects. Using attenuation‐corrected observations, in combination with the known seismic moment to constrain the absolute amplitude level at the source, we obtain an apparent source spectrum for the Ladysmith earthquake. The Ladysmith source spectrum is well described by a Brune model spectrum for an event of M 4.5 with a stress drop of ∼500 bars. Overall, the source and attenuation characteristics of the Ladysmith event were typical for regional events. The earthquake occurred within the boundaries of the Ottawa–Bonnechere graben, which suggests a reactivation of one of its faults, though it is unclear which fault was involved. The focal mechanism does not match the orientation of the most conspicuous lineaments of the area. The earthquake may have reactivated a northwest–southeast brittle fault of local extent or a ductile thrust fault of the Grenville Geological Province.

Goniopolarimetry: Space-borne radio astronomy with imaging capabilities

Abstract The principles of space-based low-frequency radio astronomy (below 50 MHz) are briefly introduced. As the wavelength range considered does not allow the use of focusing systems, goniopolarimetric (or direction-finding) techniques have been developed. These inversion techniques provide the direction of the wave vector, the polarization state and the flux of the observed electromagnetic wave. In case of spatially extended sources, we can also infer an order of magnitude of the apparent source size. These techniques are presented, and their limitations are discussed. An example from a recent study illustrates the techniques and capabilities.

On the sensitivity of older hearing-impaired individuals to acoustic attributes

In previous work, we have run a series of experiments with hearing-impaired adults to examine how age and hearing loss affect sensitivity to changes in apparent auditory source width. In two experiments, the interaural coherence of broadband noises presented over headphones and loudspeakers was varied to induce changes in width; in a third, older participants sketched the width of noise, speech, and musical stimuli in simulated rooms with varying reflection absorption. The results of those experiments showed generally decreasing sensitivities to interaural-coherence-induced changes in width as a function of age and hearing impairment. To examine how these results might influence acoustic design for the aged, a new study considers a more basic task that avoided the auditory-visual transformation implicit in sketching. Participants with normal to moderately impaired hearing will compare simulated utterances in a same/different room-discrimination task. Binaural impulse responses will be generated for open-plan buildings of varying size from the ODEON database with sources and receivers centered in each space, convolved with speech and music tokens and presented over headphones. The differences in the relationship between presbycusis and sensitivity to source width vs. general acoustical attributes will be discussed. [Work supported by the MRC and the CSO.]

Influence of manipulated early reflections on room acoustical perception

The binaural room impulse response (BRIR) can be used to study the perception of room acoustics and consists of different parts such as the direct sound, early and late reflections, and a diffuse reverberant tail. For this study, the contribution of early reflections to several perceptual attributes was investigated. For this purpose, the strength of the early reflections of recorded BRIRs were either increased or decreased. The resulting BRIRs as well as the original BRIRs have then been convolved with anechoic music signals to obtain the stimuli that were presented to the subjects in a psychoacoustic experiment. The subjects had to rate the spatial impression of these manipulated and none-manipulated signals for the perceptual attributes “Listener envelopment,”” Apparent source width,” “Distance” and “Presence.” In addition to determining the influence of manipulated early reflections on the spatial impression of a room, also a comparison was made with the perceptual effect of an artificial increase of the interaural cross-correlation. Results indicate that the perceived source width increases with increasing level of the early reflections. The effect of the level manipulations on the listener envelopment seems to be small compared to the influence of the cross-correlation.

Knowledge, attitudes, and practices of rural women from Sidama zone, southern Ethiopia concerning iodized salt, iodine and goiter (804.19)

Iodine deficiency remains a public health problem in Ethiopia and in the study area despite a proclamation in 2011 that all salt for human consumption should be iodized. A community‐based cross‐sectional study assessed prevalence of goiter and KAP of 193 randomly selected women. The mean (SD) age was 25.6 (8.1) years and the mean household size was 5.7 (2.1). Of the women 48.7% had no education, 17.6% knew some reading, 25.4% had attended or completed elementary school and 8.3% attended or completed high school. Goiter was assessed in 191 women by palpation; 23% had visible and an additional 33% had palpable goiter. Of the participants, 93.8% said they didn’t use iodized salt and 87.6% didn’t know the benefits of iodized salt. Of the 24 women who reported knowing the benefits of iodized salt, 23 said it prevents goiter but none mentioned cognitive effects. The women suggested causes of goiter to be drinking dirty water, drinking tap water, drinking rain water, but only two women said lack of iodine. The only apparent source of iodine for this population was iodized salt; however the salt contained minimal and inconsistent amounts of iodine. Lack of iodized salt may be further compounded by handling, storage, and cooking techniques. Although prevalence of goiter is high and visible in the community, knowledge of causes and prevention of iodine deficiency disorders (IDD) is minimal. Education and monitoring programs are required to combat IDD in Ethiopia.Grant Funding Source: Supported by Nestlé Foundation and Oklahoma State University