Front Hood Research Articles

Perception of English High Vowels: Duration as a Cue by Korean Speakers of English

This study examines the acoustic characteristics of English high tense and lax vowels (/i, I, u, ʊ/) and the perceptual difference of those vowels between English speakers and Korean speakers of English. In Experiment I, the first three formant values and duration of the four vowels in /hVd/ carrier were measured. The result shows that the high tense vowels have larger F2–F1 values and longer durations than high lax vowels. In Experiment II, each word’s vowel duration was manipulated into the range from 170ms to 290ms in 30ms increments. Two English speakers and six Korean speakers of English were asked to listen to a pair of tense and lax vowel words (e.g., heed_230ms–hid_170ms for the front vowel test and hood_290ms –who’d_200ms for the back vowel test), and to discriminate the pair by choosing one of the options either heed-hid or hidheed for front vowels and either who’d-hood or hood-who’d for back vowels. The results demonstrate that English speakers discriminated tense vowels from lax vowels 100% correctly regardless of the different durations, compared to 62% accuracy rate in Korean speakers of English. Most errors were found when the duration of lax vowels was lengthened and the duration of tense vowels was shortened. Therefore, the results of this study demonstrate that Korean speakers mainly rely on vowel duration as a cue to discriminate the tense and lax vowels. The pedagogical implications of this phenomenon will be discussed.

Neutron activation analysis of aerosolized sodium chloride to simulate size-fractionation of plutonium in a glovebox

Open front hoods are routinely used to mitigate a worker’s inhalation hazard. However, it has been shown that these hoods leak contaminates, especially when a worker is performing work in the hood. Quantitative measurement performed in the past does not reflect actually working conditions, but instead tends to conservatively bias the measurement by placing the sampler inside the hood or forcing the air-stream out of the hood toward the sampler. In order to accurately measure the amount of material routinely leaking from an open front hood, an air sampler was positioned in front of the hood opening and samples were taken while a routine sample digestion process was done. The digestion process involved the heating of a surrogate mixture to dryness. Samples were taken with and without a worker present during the digestion process. The samples were then analyzed at the University of Texas using neutron activation analysis. The detection level using this method was low enough to measure the amount of aerosol escaping the hood. Based on these measurements, the capture efficiency of open front hoods for PuO2 is 84%.

Numerical simulation of airflow around a variable volume/constant face velocity fume cupboard.

Three-dimensional models of a variable volume/constant face velocity fume hood were developed and numerically solved to study the effect of the sash opening and rated face velocity on the flow patterns, especially in the exposure area of a person standing in front of the fume hood. These flow details are important in assessing the containment performance of the fume hood. For this study, fully turbulent flow was assumed to enter through the front hood window and exit through the exhaust duct. The finite-difference, control-volume technique, and standard k-epsilon models were employed and solved together with the equations for the conservation of mass and momentum using FLUENT/UNS version 4.2 to obtain the flow solutions. Unobstructed flow cases, as well as the simplified two-dimensional scenarios, also were investigated for comparison. Results indicated that there is no occurrence of recirculation leading to concentration buildup within the region between the person and fume hood entrance. Also, in conformance with other studies, the recirculating flow volume inside the hood decreased with increasing sash openings.