Responses to two-tone stimuli were recorded from auditory-nerve fibers in anesthetized cats. One tone, the suppressor, was set at a frequency above characteristic frequency and was fixed in intensity. A second tone was set at an excitatory frequency and was varied in intensity. The suppressor tone, when set at a sufficient level, always reduced the response to the excitatory tone by an amount equivalent to a fixed number of decibels, regardless of the excitatory tone's intensity. Estimates of suppression magnitude were derived from shifts in rate-intensity function obtained when the suppressor tone was present relative to the functions obtained for the excitatory tone alone. When suppressor-tone intensity was increased, suppression magnitude likewise increased. When the two tones were increasingly separated in frequency, either by varying the excitor or by varying the suppressor, suppression magnitude decreased monotonically. Suppression behaved in the same manner regardless of whether suppresor tone was excitatory or nonexcitatory. When frequency separation was small enough and when both tones were above the neuron's characteristic frequency, responses synchronized to low-order combination tones could be elicited. These responses usually possessed different rate-intensity characteristics and resulted in estimates of suppression magnitude which were spuriously low. When frequency separation is normalized with regard to position of traveling wave maxima within the cochlear duct, the magnitude of two-tone suppression for a given suppressor-tone intensity is seen to be frequency independent.

Developing a profound understanding of the combustion characteristics of the cold-start phase of a Direct Injection Spark Ignition (DISI) engine is critical to meeting increasingly stringent emissions regulations. Computational Fluid Dynamics (CFD) modeling of gasoline DISI combustion under normal operating conditions has been discussed in detail using both the detailed chemistry approach and flamelet models (e.g. the G-Equation). However, there has been little discussion regarding the capability of the existing models to capture DISI combustion under cold-start conditions. Accurate predictions of cold-start behavior involves the efficient use of multiple models - spray modeling to capture the split injection strategies, models to capture the wall-film interactions, ignition modeling to capture the effects of retarded spark timings, combustion modeling to accurately capture the flame front propagation, and turbulence modeling to capture the effects of decaying turbulent kinetic energy. The retarded spark timing helps to generate high heat flux in the exhaust for the faster catalyst light-off during cold-start. However, the adverse effect is a reduced turbulent flame speed due to decaying turbulent kinetic energy. Accordingly, developing an understanding of the turbulence-chemistry interactions is imperative for accurate modeling of combustion under cold-start conditions. In the present work, combustion characteristics during the cold-start, fast-idle phase is modeled using the G-Equation flamelet model and the RANS turbulence model. The challenges associated with capturing the turbulent-chemistry interactions are explained by tracking the flame front travel along the Borghi-Peters regime diagram. In this study, a modified version of the G-Equation combustion model for capturing cold-start flame travel is presented.

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A new method oeor measuring electrical-impedance changes that are elicited by tonal stimuli in the cochlea ooe the anesthetized guinea pig has been developed. Constant-amplitude currents ooe low-frequency sinusoidal waveoeorm are delivered to scala media simultaneously with tonal stimuli. In the signal recorded from scala media, energy is detected at frequencies equal to the sum and difference ooe the applied frequencies. This energy is interpreted as due to changes A R in the resistance ooe the scala media that are synchronized with the acoustic waveoeorm. The maximum magnitude ooe the change varies from about 0.2% in turn I to about 1% in turn III. During normal conditions, striking parallels exist between the behavior ooe A R and CM as both frequency and intensity are varied. However, under asphyxic conditions, the observed change in A R is usually much less than that in CM. The results are shown to be qualitatively, though not quantitatively, consistent with a two-dimensional, variable-resistance model ooe the cochlea. PACS numbers: 43.63.Nc, 43.63.Rf approximately 100 •2, about 1% of the total impedance, was observed. Unfortunately, the sinusoidal current technic•ue also has limitations.Owing to capacitive coupling between the scala-media electrodes, the frequency of electrical stimulation is usually kept well below I kHz (see below). As the detection technique used by Strelioff et al. (1971) requires that the frequency of the electrical signal be considerably greater than that of the acoustic signal (see below), the acoustic signal they used was limited to very low frequencies.In addition, the signal-to-noise ratio is not good, with only approximately 14 dB of dynamic range available for the impedance-change measurements.The present report describes resistance changes measured with the sinusoidal current technique. We have used a new method of processing data that has reduced many of this technique's previous limitations and has allowed it to be used over a much wider range of stimulus parameters.A preliminary report has been given previously (Geisler et al.; 1975). I. METHODS A. Animal preparation and equipmentYoung adult guinea pigs of dark pigmentation weighing between 200 and 500 g were anesthetized with sodium pentobarbital (Diabutal). A presurgical dose of atropine 1557

Computational Fluid Dynamics (CFD) modeling of gasoline spark-ignited engine combustion has been extensively discussed using both detailed chemistry mechanisms (e.g., SAGE) and flamelet models (e.g., the G-equation). The models have been extensively validated under normal operating conditions; however, few studies have discussed the capability of these models in capturing DISI combustion under cold-start conditions. A cold-start differs from normal operating conditions in various respects, such as (1) having highly retarded spark timing to help generate a high heat flux in the exhaust for a rapid catalyst light-off; (2) having split-injection strategies to ensure a favorable stratification at the vicinity of the spark plug and reduced film formation; and (3) having optimized valve timings for reduced NOx emissions via increased internal residuals and reduced hydrocarbon (HC) emissions via prolonged oxidation of the combustion products. The retarded spark timing introduces the adverse effect of a decaying turbulence field, which results in a reduced turbulent flame speed. The analysis of all these factors happening inside the cylinder appears complicated at first glance; however, it could be made possible by efficient use of the existing CFD models. The current study explored the capability of the SAGE detailed chemistry model in capturing cold-start flame travel in a DISI engine. The results were then compared against the G-equation-based GLR model, which has been validated for excellent predictions of the DISI cold-start combustion as shown by Ravindran et al. The flame travel was captured on a Borghi-Peters diagram to find that the flame travels through corrugated, wrinkled, and laminar regimes. In order to fully evaluate the capability of the detailed chemistry model in predicting such changing turbulence-chemistry interactions, it will need to be studied individually in each regime; however, the scope of the current paper is limited to the study of the model behavior in the laminar regime, which will be shown to be important for DISI engine cold-start. The SAGE detailed chemistry model, with a toluene reference fuel (TRF) mechanism validated for gasoline laminar flame speeds, was found to significantly under-predict the flame propagation speeds because of the effects of numerical viscosity and discrepancies in capturing molecular diffusion. The causes and effects of this under-prediction and the ways in which this can be improved are presented in the paper.