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Q T Nguyen

Publications and source records attributed to Q T Nguyen.

42 records · Page 3Linked to original sources
PubMed1992

Discrimination of narrow-band spectra. I: Spectral weights and pitch cues.

The ability to detect changes in the spectral shape of narrow-band tonal complexes (spectral profiles) is examined. The standard consists of three tones of equal intensity; thresholds for detecting an increment in the level of the central, 1000-Hz tone are estimated. A roving-level procedure is used in order to impose a statistical limit on thresholds that can be obtained by basing discriminations on absolute intensity. Estimated thresholds are consistently below this limit, thus indicating the use of other cues. Generally, thresholds are constant for bandwidths ranging from less than a critical band to greater than several octaves. Spectral weight estimates, however, are highly dependent on bandwidth, providing evidence that the discrimination of narrow-band spectra involves different auditory processes than those used to discriminate wideband spectra. Additional data show that pitch cues are important within a restricted range of intermediate bandwidth, but not for wideband or very narrow-band spectra. A version of the EWAIF model involving off-frequency listening is proposed to account for the results.

Adolescent↗
PubMed1991

Demonstration of a divergent transcript from the bidirectional heavy chain immunoglobulin promoter VH441 in B-cells.

The mouse heavy chain immunoglobulin promoter VH441 can lead in vitro to bidirectional transcription, due to a symmetrical organization of immunoglobulin heavy chain promoters with two TATA-like sequences bracketing the upstream promoter element ATGCAAAT (the so called octamer). We demonstrate here that divergent transcription also occurs in vivo in mature B cells from a myeloma which expresses the VH441 gene and even from the spleen of BALB/c mice. The level of VH441 divergent transcript increases in the spleen of BALB/c mice after immunisation by beta-(1,6)-galactan, showing that it is expressed in B cells which actively transcribe the VH441 gene. The divergent transcript has been characterized: its major transcription start site was mapped within 33 base pairs from the divergent TATA-like region, it is unspliced and not polyadenylated. In the light of these results, the functions of the divergent transcript and the bidirectional promoter are discussed.

Animals↗
PubMedDate not supplied

A Windows software package to record from voltage-clamped Xenopus oocytes.

We have written a software package to record, display and analyze membrane currents elicited by neurotransmitter receptors or voltage-activated channels in voltage-clamped Xenopus oocytes. This suite, which consists of 4 applications, runs on IBM-PC compatible microcomputers under Windows 3.1. The recording programs use Direct Memory Access (DMA) to access the analog-digital board. The first program, NicPulse, is aimed at studying voltage-activated channels. It delivers voltage steps to the voltage-clamp and records the resulting membrane current. The second program, NicScope, emulates a dual-trace digital oscilloscope. It operates either in continuous or triggered mode, and is used chiefly to display neurotransmitter-induced responses in oocytes. The third recording program, VRamp, automatically determines the voltage-current relationship of drug-activated responses (I/V curve), by applying a voltage ramp and recording the subsequent clamping current. The last program, NicView, is designed to analyze records taken with NicScope and NicPulse. The present paper will discuss several issues regarding the design of these programs, and will give a brief description of each application.

Animals↗
PubMedDate not supplied

Profile analysis: detecting dynamic spectral changes.

This paper explores how amplitude modulation influences the detection of changes in spectral shape. We generally used a complex of 21 equal-amplitude components, the lowest frequency was 200 Hz, the highest 5000 Hz, with equal logarithmic spacing between components. The signal was an increase in level of one or more components of the complex. The overall level of the sound varied randomly over a 20-dB range. Three experiments are reported. In the first, we determined how the modulation of a single-frequency component influenced the detection of amplitude change at that region. In the second experiment, the signal was an alteration of the entire spectrum and that alteration was subjected to various forms of amplitude modulation. In neither experiment did modulation generally increase the detectability of the signal. Finally, in the third experiment, we determined the effects of modulating the 'signal' and 'nonsignal' parts of the spectrum in different relative phases. The results of this experiment showed that the relative phase is important only for modulation rates slower than about 40 Hz. For faster rates, the temporal structure of the spectrum is unimportant. Thus, for modulation rates above 40 Hz, only the power spectrum of the stimulus is critical.

Acoustic Stimulation↗
PubMedDate not supplied

Prevalence of cryoglobulins and hepatitis C virus infection in HIV-infected patients.

PURPOSE AND METHODS: In order to evaluate the prevalence of positive hepatitis C virus (HCV) serology and cryoglobulinemia in human immunodeficiency virus (HIV)-infected patients, the prevalence and the clinical significance of cryoglobulinemia were prospectively studied in a cohort of 86 HIV-infected subjects seen as outpatients. They were compared to a control group consisting of 101 HIV-HCV+ patients being followed at the same hospital. RESULTS: HCV serology was positive in 53/86 (61.6%) patients, 25 (47.2%) of whom had detectable cryoglobulins in their sera although only 1 had clinical symptoms consistent with cryoglobulinemia. Cryoglobulinemia was also detected in 9/33 (27.3%) HCV- patients, with only one of them presenting clinical symptoms. Although the mean cryoglobulin concentration was lower for HIV+ patients than in controls (268 versus 585 mg/l, p < 0.01), their prevalence (39.5% and 27.2%, respectively) was higher (p < 0.03). CONCLUSION: Cryoglobulinemia is frequently detected in HIV-infected patients, regardless of their HCV serology, but is poorly correlated with clinical symptoms.

Adult↗