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At least 595 records · Page 33Linked to original sources
PubMed1985

Toward a standard for hearing conservation for underwater and hyperbaric environments.

Exposure of divers to intense noise in water is increasing, yet no general hearing-conservation standard for such exposures exists. This paper summarizes three theories of underwater hearing, the tympanic, bone-conduction, and dual path theories, and reviews empirical data in order to identify some requirements such a standard must meet. Among problems considered are hearing sensitivity in water, the frequency and dynamic ranges of the water-immersed ear, and non-auditory effects of underwater sound. It was concluded that no well-developed theoretical basis exists for extrapolating current hearing-conservation standards for air-borne noise to the underwater situation; the existing empirical evidence, except within the frequency range of 1.5-3.5 kc/s, is too scant to predict what levels of underwater noise would be safe for divers; the empirical data on underwater hearing suggest that the frequency range covered by an appropriate standard must be much broader, for both low and high frequencies, than is the case in air; in order to establish an appropriate standard, further research is required on the dynamic range of the ear in water; problems must be solved with shifts in the resonance frequency of the ear consequent to the introduction of helium-oxygen mixtures or other exotic gases and pressures during dry-helmet diving or during simulated underwater excursions in dry hyperbaric chambers; underwater noise exposure may involve hazards to other body systems than the ear; and some noise exposure conditions may interfere with job performance of divers.

Atmospheric Pressure↗
PubMed1982

Temporal acuity in auditory function in the rat: reflex inhibition by brief gaps in noise.

The acoustic startle reflex in the rat is inhibited if a relatively weak stimulus precedes the startle-eliciting tone burst. This research explored the effect of brief silent periods (gaps) in white noise on the startle reflex, in order to describe the limits of temporal resolution in the auditory system of the rat. Brief silent periods did depress reflex behavior, and two responsible processes were identified. One was most evident at a 190-msec lead time between gap and startle tone. It yielded a linear decrement in reflex expression over a dynamic range of 0-7 msec, and an estimate for the threshold of temporal acuity of 3.5 msec. The second was evident primarily at a 40-msec interstimulus interval and had a linear effect over a dynamic range of at least 40 msec. Very brief gaps had a greater inhibitory effect at the 190-msec interval between gap and startle stimulus; prolonged gaps had their greater effect at the 40-msec interval. The first process was identified as reflex inhibition, which is sensitive to the sensory properties of the lead stimulus. The second process was identified as sensory adaptation, produced by noise exposure but unmasked by silence.

Adaptation, Physiological↗
PubMed2004

An effective kinetic representation of fluctuation-driven neuronal networks with application to simple and complex cells in visual cortex.

A coarse-grained representation of neuronal network dynamics is developed in terms of kinetic equations, which are derived by a moment closure, directly from the original large-scale integrate-and-fire (I&F) network. This powerful kinetic theory captures the full dynamic range of neuronal networks, from the mean-driven limit (a limit such as the number of neurons N --> infinity, in which the fluctuations vanish) to the fluctuation-dominated limit (such as in small N networks). Comparison with full numerical simulations of the original I&F network establishes that the reduced dynamics is very accurate and numerically efficient over all dynamic ranges. Both analytical insights and scale-up of numerical representation can be achieved by this kinetic approach. Here, the theory is illustrated by a study of the dynamical properties of networks of various architectures, including excitatory and inhibitory neurons of both simple and complex type, which exhibit rich dynamic phenomena, such as, transitions to bistability and hysteresis, even in the presence of large fluctuations. The implication for possible connections between the structure of the bifurcations and the behavior of complex cells is discussed. Finally, I&F networks and kinetic theory are used to discuss orientation selectivity of complex cells for "ring-model" architectures that characterize changes in the response of neurons located from near "orientation pinwheel centers" to far from them.

Computer Simulation↗
PubMed1985

An amperometric detector for use with small-bore liquid chromatographic columns.

A miniaturized electrochemical flow cell for amperometric detection in liquid chromatography has been designed to meet the requirement of low volumetric dispersion when using small-bore columns. The volume of the thin-layer cell is in the range 10-50 nl, depending on the spacer dimensions, with the electrode area being about 1 mm2. The cell is constructed from glass and designed in such a way that the working electrode can be mounted without alterations to its surface state. The flow-rate dependence, contribution to peak dispersion and linear dynamic range were investigated. After separation on a 250 X 1 mm I.D. column, a detection limit for dopamine of about 0.15 pg was achieved with a linear dynamic range of 10(6). The variance of the extra-column dispersion was determined to be less than 0.3 microliter2, including injector and connecting capillaries. The applicability of the detector is illustrated with the detection of dopamine and its major metabolites, dihydroxyphenylacetic acid and homovanillic acid, and of Met- and Leu-enkephalin in samples of biological origin.

Animals↗
PubMed2002

Quantitative determination of polar and ionic compounds in petroleum fractions by atmospheric pressure chemical ionization and electrospray ionization mass spectrometry.

The capabilities of atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) methods for quantitative analysis of polar and ionic compounds in petroleum fractions have been examined. The requirements of the analysis for sensitivity, linear dynamic range, and structural characterization have been discussed. ESI was found to be approximately two orders of magnitude more sensitive than APCI and is most suitable for the detection of analytes in weak concentrations. Equivalent relative linear dynamic ranges were observed by the two methods (at least three orders of magnitude). For the relatively high analyte concentrations examined here (e.g., 1-100 ppm or higher), the absolute area counts increased linearly with the analyte amount only in APCI, making this method more attractive for quantitative liquid chromatography/mass spectrometry (LC/MS) applications. Nevertheless, a wider range of ionic compounds can be detected by ESI than by APCI.

Air Pressure↗
PubMed1987

Enzyme-amplified immunoassays.

The sensitivity of enzyme immunoassays may be enhanced by the use of enzyme-amplification. This technique uses the enzyme label in the immunoassay to provide a trigger substance for a secondary system that can generate a large quantity of coloured product. Two examples of enzyme amplifiers are described, using either a substrate cycle with phosphorylated hexose sugars, or a redox cycle involving the coenzyme NAD(+). The redox enzyme-amplifier has a detection limit of less than one attomole for the enzyme label, alkaline phosphatase. The limited dynamic range of enzyme-amplified immunoassays may be overcome by kinetic analysis of the colour development in the enzyme-amplifier, to add at least a further order of magnitude to the range of directly measured analyte concentrations in the immunoassay. This is illustrated in an enzyme-amplified immunoassay for human thyroid stimulating hormone. Amperometric measurement of the enzyme-amplifier provides a method to extend the dynamic range still further and compares favourably with the performance of a gamma counter, a luminometer or a fluorimeter.

Journal Article↗
PubMed2001

Psychophysics of a prototype peri-modiolar cochlear implant electrode array.

Psychophysical measurements were performed in three hearing-impaired adult subjects implanted with a CI22 cochlear prosthesis (Cochlear Ltd.) fitted with a developmental peri-modiolar electrode array. The array was manufactured with a curvature approximating that of the inner wall of the scala tympani but, after straightening and insertion, lay on average about half way between the inner and outer walls of the scala. All subjects were tested with bipolar stimulation; two were also tested with monopolar, employing the most basal electrode as the return. Maximum comfortable level and threshold reduced with decreasing distance of electrode from the modiolus, whereas dynamic range increased. The linearity of the loudness growth function did not vary significantly with electrode position but the function was more non-linear for lower maximum comfortable levels. Current level discrimination, normalized with respect to dynamic range, improved with decreasing distance of electrode from the modiolus in two subjects. Pitch varied regularly with insertion depth of the stimulated electrode for bipolar stimulation in two subjects and also for monopolar stimulation in one subject. Electrode discrimination was enhanced by closeness to the modiolus. Whereas the forward masking patterns for bipolar stimulation of electrodes close to the modiolus had a sharp double-peaked structure, those for monopolar stimulation were flatter and had a single peak.

Adult↗
PubMed2000

In situ assembled mass-transport controlling micromembranes and their application in implanted amperometric glucose sensors.

Micromembranes were assembled by sequentially chemisorbing polyanions and polycations on miniature (5 x 10(-4) cm2) enzyme electrodes. The sequential chemisorption process allowed the simultaneous tailoring of their sensitivity, dynamic range, drift, and selectivity. When assembled on tips of 250-microm-diameter gold wires coated with redox polymer-"wired" glucose oxidase, they allowed tailoring of the glucose electrodes for > 2 nA/mM sensitivity; 0-30 mM dynamic range; drift of < or =5% per 24 h at 37 degrees C at 15 mM glucose concentration; and < or =5% current increment by the combination of 0.1 mM ascorbate, 0.2 mM acetaminophen, and 0.5 mM urate. The membranes also retained transition metal ions that bound to and damaged the redox polymer "wiring" the enzyme. The electrodes were tested in the jugular veins and in the intrascapular subcutaneous region of anaesthetized and heparinized nondiabetic Sprague-Dawley rats, in which rapid changes of glycemia were forced by intravenous injections of glucose and insulin. After one-point in vivo calibration of the electrodes, all of the 152 data points were clinically accurate when it was assumed that after insulin injection the glycemia in the subcutaneous fluid lags by 9 min behind that of blood withdrawn from the insulin-injected vein.

Animals↗
PubMed1989

[Electric stimulation of auditory nerve fibers. Experimental study].

The authors tested in animal experiments the effectiveness of electrical stimulation of acoustic nerve fibres. To guinea pigs platinum-iridium electrodes were implanted in the round window of the cochlea. The receptors of the inner ear were functionally eliminated by the local application of the ototoxic antibiotic gentamicin. Cortical responses produced by electric stimulation of the contralateral ear and acoustic stimulation of the ipsilateral intact ear were recorded. The threshold for producing a cortical response by the electric stimulus was lowest at the frequency of 0.5 kHz and rose with the rising frequency. This relationship was the same for extracochlear and intracochlear stimulation, the absolute threshold values of the current in the same animal were, however, as a rule lower on intracochlear stimulation. The dynamic range of responses to electrical stimulation (difference between threshold intensity of the current and the intensity which produces a painful response of the animal) was 6-20 dB, as compared with 80-100 dB of the dynamic range for acoustic stimulation. The results of the experiments were used in the preparation of the Czechoslovak cochlear neuroprosthesis and serve as a basis for the further development of the implant.

Animals↗
PubMed2001

The effect of monaural middle ear destruction on postnatal development of auditory response properties of mouse inferior collicular neurons.

This study examined the effect of monaural middle ear destruction on postnatal development of auditory response properties of inferior collicular (IC) neurons of the laboratory mouse, Mus musculus. Monaural middle ear destruction was performed on juvenile and adult mice and the auditory response properties of neurons in both ICs were examined 4 weeks thereafter. IC neurons of control mice typically had lower minimum thresholds, larger dynamic ranges and greater Q(10) values than IC neurons of experimental juvenile and adult mice. In experimental mice, neurons in the ipsilateral IC (relative to the intact ear) typically had longer latencies, higher minimum thresholds, and smaller dynamic ranges than neurons in the contralateral IC. In experimental adult mice, neurons in the ipsilateral IC had sharper frequency tuning curves than neurons in the contralateral IC. Clear tonotopic organization was only observed in the IC of control mice and experimental adult mice. However, the correlation of increasing minimum threshold with best frequency was observed for IC neurons in control mice but not in experimental juvenile and adult mice. Possible mechanisms for these different response properties are discussed.

Acoustic Stimulation↗
PubMed2005

Indirect flat-panel detector with avalanche gain: fundamental feasibility investigation for SHARP-AMFPI (scintillator HARP active matrix flat panel imager).

An indirect flat-panel imager (FPI) with avalanche gain is being investigated for low-dose x-ray imaging. It is made by optically coupling a structured x-ray scintillator CsI(Tl) to an amorphous selenium (a-Se) avalanche photoconductor called HARP (high-gain avalanche rushing photoconductor). The final electronic image is read out using an active matrix array of thin film transistors (TFT). We call the proposed detector SHARP-AMFPI (scintillator HARP active matrix flat panel imager). The advantage of the SHARP-AMFPI is its programmable gain, which can be turned on during low dose fluoroscopy to overcome electronic noise, and turned off during high dose radiography to avoid pixel saturation. The purpose of this paper is to investigate the important design considerations for SHARP-AMFPI such as avalanche gain, which depends on both the thickness d(Se) and the applied electric field E(Se) of the HARP layer. To determine the optimal design parameter and operational conditions for HARP, we measured the E(Se) dependence of both avalanche gain and optical quantum efficiency of an 8 microm HARP layer. The results were used in a physical model of HARP as well as a linear cascaded model of the FPI to determine the following x-ray imaging properties in both the avalanche and nonavalanche modes as a function of E(Se): (1) total gain (which is the product of avalanche gain and optical quantum efficiency); (2) linearity; (3) dynamic range; (4) gain nonuniformity resulting from thickness nonuniformity; and (5) effects of direct x-ray interaction in HARP. Our results showed that a HARP layer thickness of 8 microm can provide adequate avalanche gain and sufficient dynamic range for x-ray imaging applications to permit quantum limited operation over the range of exposures needed for radiography and fluoroscopy.

Cesium↗
PubMed2004

Improving the diffuse optical imaging spatial resolution of the cerebral hemodynamic response to brain activation in humans.

We compare two geometries of sources and detectors for optimizing the diffuse optical imaging resolution of brain activation in humans. Because of limitations in the instruments' dynamic range, most diffuse optical brain activation images have used only nonoverlapping measurements. We demonstrate theoretically and with a human experiment that a simple geometry of sources and detectors can provide overlapping measurements within the limitation of instrumentation dynamic range and produce an image resolution and localization accuracy that is twofold better.

Adult↗
PubMed1999

Electrode complications in 100 adults with multichannel cochlear implants.

At switch-on (first post-operative stimulation of the implant) and during subsequent reprogramming, electrodes can, in some patients, be found to be non-functional or to be performing sub-optimally for a number of reasons. This paper examines the reasons for the poor performance of these electrodes by means of a retrospective analysis of 100 patient records. All of these patients received the Nucleus multichannel device. The most common reason for an electrode to require de-activation was found to be facial nerve stimulation, with poor sound quality and pain also being very common. Other reasons included absence of auditory stimulation, vibration, reduced dynamic range, throat sensations, absence of loudness growth or dizziness. The occurrence of these reasons along the electrode array was examined, more basal electrodes being found to be non-functional as a result of having a small dynamic range or poor sound quality. Pain and vibration were found to occur throughout the array and the more apical electrodes were found to be non-functional as a result of facial nerve stimulation. It is suggested that the electrodes at the basal end of the array are likely to be extra-cochlear or are at the site of the most cochlear damage, whereas the more apical electrodes lie in closer proximity to the facial nerve.

Cochlear Implantation↗
PubMed1998

Rapid estimation of octanol-water partition coefficients of pesticides by micellar electrokinetic chromatography.

Micellar electrokinetic chromatography (MEKC) was evaluated as a new technique for the rapid estimation of octanol-water partition coefficient (logKow). Retention measurements for more than 40 reference pesticides with varied structural characteristics and hydrophobicity were carried out in two MEKC systems, based on sodium dodecyl sulfate (SDS) and sodium cholate (SC), respectively. To enable an accurate determination of capacity factors in the SC-MEKC system, cypermethrin (a synthetic pyrethroid insecticide) was utilized instead of Sudan III as the SC micelle tracer, since a few highly hydrophobic pesticides were found to elute after Sudan III. The linear correlation between logarithmic capacity factor (logk') and logKow in the two systems was examined. It was found that, under the typical buffer condition (10 mM sodium phosphate with 60 mM surfactant, pH 7.0), the SDS-MEKC system provided a somewhat wider dynamic range for hydrophobicity (logKow from -1.0 to 4.5). However, the correlation of logk' with logKow was not very high when all the reference pesticides were included in one single calibration set. For the SC-MEKC system, the dynamic range for logKow was in the range of 1.0-5.5, and a good linear correlation existed between logk' and logKow, even when all reference pesticides were incorporated into a single calibration group. By comparing the regression line of the reference pesticides with that of a group of simple aromatic derivatives, it was discovered that molecular size and functionality posed a less significant effect on the measurement of logKow in the SC-MEKC system than in the SDS-MEKC system. Thus, SC-MEKC shall be the system of choice for the estimation of logKow. The typical error on logKow determination using the current MEKC technique was within 0.5 units, suggesting that MEKC can be a valuable complement to reversed phase high performance liquid chromatography (RP-HPLC) for the indirect determination of logKow. Besides maintaining all the advantages of the HPLC approach, the MEKC technique showed some unique benefits, such as better inter-column reproducibility, higher throughput, and less handling of toxic pesticides and solvents.

Chromatography↗
PubMed2004

High-frequency oscillations and seizure generation in neocortical epilepsy.

Neocortical seizures are often poorly localized, explosive and widespread at onset, making them poorly amenable to epilepsy surgery in the absence of associated focal brain lesions. We describe, for the first time in an unselected group of patients with neocortical epilepsy, the finding that high-frequency (60-100 Hz) epileptiform oscillations are highly localized in the seizure onset zone, both before and temporally removed from seizure onset. These findings were observed in all six patients with neocortical epilepsy out of 23 consecutive patients implanted with intracranial electrodes for pre-surgical evaluation during the study period. The majority of seizures (62%) in these patients were anticipated by an increase in high-frequency activity in the 20 min prior to neocortical seizure onset. Contrary to observations in normal brain, high-frequency activity was strongly modulated by behavioural state, and was maximal during slow-wave sleep, which may explain the propensity for neocortical onset seizures to begin during sleep. These findings point to an important role for neuromodulatory circuits, probably involving the thalamus, in mechanisms underlying seizure generation in neocortical epilepsy. These findings demonstrate that high-frequency epileptiform oscillations may prove clinically useful in localizing the seizure onset zone in neocortical epilepsy, for identifying periods of increased probability of seizure onset, and in elucidating mechanisms underlying neocortical ictogenesis. Confirmation that prolonged bursts of high-frequency activity may predict focal onset neocortical seizures will require prospective validation on continuous, prolonged recordings in a larger number of patients. Importantly, the results show that the dynamic range utilized in current clinical practice for localization of epileptogenic brain largely ignores fundamental oscillations that are signatures of an epileptogenic brain. It may prove that many currently available clinical EEG systems and EEG analysis methods utilize a dynamic range that discards clinically important information.

Analysis of Variance↗
PubMed2026

Monitoring kinetic changes and restriction of influenza A virus RNA species during infection using a Flu-Stranded CRISPR platform.

UNLABELLED: Influenza A virus (IAV) generates three closely related RNA species: viral RNA (vRNA), complementary RNA (cRNA), and messenger RNA (mRNA), whose strand-specific quantification remains limited by sensitivity and quantitative dynamic range, particularly at low RNA abundance. Here, we developed Flu-Stranded CRISPR-Cas12a, a strand-specific detection platform integrating tagged reverse transcription, segment-specific PCR, and Cas12a collateral cleavage to support quantitative analysis of all three RNA species across a broad dynamic range. The assay enables reliable detection down to 102 copies per reaction, extending the lower quantitative boundary relative to both SYBR Green and TaqMan reverse transcription quantitative PCR (RT-qPCR) under matched conditions. Validated in infected cell lines, murine lung tissues, and clinical nasopharyngeal specimens, the platform enabled subtype-discriminating, strand-resolved detection, including samples near or below the quantitative range of SYBR Green RT-qPCR. Using finely resolved infection time-course analyses in NP and NA segments, we identified a reproducible early vRNA decline within the early post-infection phase. This decline was partially attenuated in RIG-I knockout A549 cells, while subsequent vRNA accumulation was enhanced, consistent with a modulatory rather than essential role for RIG-I in early viral RNA dynamics. Subcellular fractionation localized this decline to cytoplasmic incoming genomes. In contrast, importazole-mediated inhibition of nuclear import abolished vRNA recovery without affecting the early decline, indicating that nuclear entry functionally separates early genome reduction from subsequent productive replication. These findings establish Flu-Stranded CRISPR-Cas12a as a strand-resolved framework for monitoring IAV RNA dynamics and reveal an early window of genome vulnerability during cytoplasmic transit that shapes infection outcome. IMPORTANCE: The early fate of incoming influenza virus genomes remains unclear, limiting our understanding of how infection is established or aborted in host cells. We developed Flu-Stranded CRISPR-Cas12a, a strand-specific platform for sensitive and quantitative analysis of influenza viral RNA (vRNA), complementary RNA (cRNA), and messenger RNA (mRNA) across experimental and clinical samples. Using high-resolution time-course analysis, we identified a reproducible early decline in vRNA during the post-entry phase. Our data suggest that this early genome loss arises from multiple processes, with RIG-I acting as a modulatory factor rather than a primary driver. Subcellular fractionation localized this effect to cytoplasmic incoming genomes, whereas importin-&#x3b2;-mediated nuclear entry was required for subsequent vRNA recovery. These findings support a model of an early cytoplasmic phase of genome attrition that is distinct from replication and provide a framework for understanding early influenza RNA kinetics and for guiding strand-resolved diagnostics and antiviral evaluation.

CRISPR-Cas12a↗
PubMed2005

Comparing monolithic and microparticular capillary columns for the separation and analysis of peptide mixtures by liquid chromatography-mass spectrometry.

A mixture of ten proteins was trypsinized and injected onto poly-(styrene-divinylben-zene) monolithic columns (60 x 0.20 or 0.10 mm ID) and a column packed with C18 silica particles (75 x 0.075 mm ID), respectively. The columns were eluted at 200-2000 nL/min with gradients of ACN in 0.050% TFA. Eluting peptides were detected by ESI-MS/MS and subsequently identified by database searching. The 100 microm ID monolithic column showed the highest cumulative Mowse scores based on the highest ion scores for the peptides and the largest number of identified peptides. It is shown that the number of identified peptides strongly depends on the dynamic range within the peptide mixture. In consequence, all proteins were identified in a mixture of relatively balanced analyte amounts (12.5-80 fmol) whereas only peptides for six out of ten proteins were found in a sample of high-dynamic range (0.65-270 fmol). The 100 microm monolithic column showed the highest reproducibility for peptide identifications in three consecutive runs. Depending on sample amount, 57-72% of the identified peptides were detectable in each of the three runs of triplicate analyses. The results demonstrate the high suitability of 100 microm monolithic columns for high-resolution peptide separations in proteomic research.

Amino Acid Sequence↗
PubMed1994

Effects of stimulus level on nonspectral frequency discrimination by human subjects.

Frequency difference limens were determined as a function of reference-stimulus level for pulsatile electrical stimuli in 5 postlingually deaf human subjects with Nucleus-22 cochlear implants and for sinusoidally amplitude-modulated acoustic white noise stimuli in 4 normal-hearing humans. Subjects were tested at levels throughout the dynamic range and extending to the lowest detectable levels. Response stability was measured over the course of 10 sessions. For electrical stimulation in the deaf ears, difference limens decreased as a function of level throughout much or all of the dynamic range of hearing. This result contrasts with the case for nonspectral acoustic stimulation of normal-hearing subjects, where nonspectral frequency difference limens were strongly affected by level only near the detection threshold. These data suggest differences in the acoustic and electrical response spaces that must be considered in the design of auditory prosthesis processors.

Acoustic Stimulation↗