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At least 1,531 records · Page 85Linked to original sources
PubMed2002

Noise in miniature microphones.

The internal noise spectrum in miniature electret microphones of the type used in the manufacture of hearing aids is measured. An analogous circuit model of the microphone is empirically fit to the measured data and used to determine the important sources of noise within the microphone. The dominant noise source is found to depend on the frequency. Below 40 Hz and above 9 kHz, the dominant source is electrical noise from the amplifier circuit needed to buffer the electrical signal from the microphone diaphragm. Between approximately 40 Hz and 1 kHz, the dominant source is thermal noise originating in the acoustic flow resistance of the small hole pierced in the diaphragm to equalize barometric pressure. Between approximately 1 kHz and 9 kHz, the noise originates in the acoustic flow resistances of sound entering the microphone and propagating to the diaphragm. To further reduce the microphone internal noise in the audio band requires attacking these sources. A prototype microphone having reduced acoustical noise is measured and discussed.

Amplifiers, Electronic↗
PubMed1983

A miniature electrode for surface electromyography during speech.

A miniature recessed (i.e., cup) surface EMG electrode intended for use in the perioral region during speech has been constructed and tested. In addition to its small size and low mass, a custom acrylic electrode housing features an extruded design to yield secure attachment to the skin with skin cement rather than with conventional double adhesive collars. A durable, commercially manufactured disk of homogeneous silver and silver chloride was utilized to optimize bioelectric characteristics and durability. In relation to the commonly used fine-wire intramuscular electrode composed of platinum-iridium, this surface electrode demonstrates comparable bioelectric performance in perioral applications including low, stable, and well-matched skin-electrode impedance, a low noise floor, a surprisingly wide bandwidth, and good signal-to-noise ratios.

Electromyography↗
PubMed1993

Miniature microphone probe tube measurements in the external auditory canal.

The use of a miniature microphone probe tube for sound-pressure level measurements in the outer earcanal was studied in four experiments. The main reason was to evaluate this method for clinical applications and for measurements of hearing protector attenuation. All measurements were registered in 1/3-oct bands. The dynamic range, frequency response of the microphone system, the insertion loss of the probe tube walls, and the influence of the probe tube in the ear canal on the sound-pressure level were examined. The first experiment attempted to determine an optimal placement of the probe tube in the earcanal. Sound-pressure levels resulting from a known free-field sound stimulus were measured at 12 different positions in the earcanal of human subjects. The results indicated that the position which is least sensitive for small movements of the probe tube on the measure was within 1 to 3 mm of the tympanic membrane. In a second experiment the changes in sound transfer function to the tympanic membrane caused by the microphone itself, when positioned just outside the ear canal entrance, were studied for 72 angles of sound incidences in ten subjects. A few minor but significant changes were observed with the microphone in this position. In a third experiment, sound transfer functions were measured from free sound field to the tympanic membrane in 19 subjects. The measurements were performed in 1/3-oct frequency bands (0.2 to 20 kHz) with sound incidences from 24 azimuthal positions and for each of these, three different elevations. The inter- and intrasubject-variability are analyzed and discussed. Finally, the reliability of probe tube microphone measurements was evaluated by repeated measurements of the sound transfer function, five times in ten subjects with the sound incidence from one position. The results indicated very small variations between repeated measurements.

Acoustic Stimulation↗
PubMed2003

Suppression of L-type voltage-gated calcium channel-dependent synaptic plasticity by ethanol: analysis of miniature synaptic currents and dendritic calcium transients.

Intoxicating concentrations of ethanol inhibit N-methyl-d-aspartate (NMDA) receptor-dependent long-term potentiation, an interaction thought to underlie a major component of the central nervous system actions of ethanol. Another form of synaptic potentiation involving activation of L-type dihydropyridine-sensitive voltage-gated calcium channels (VGCCs) has been described, but very little information concerning ethanol effects on VGCC-dependent synaptic potentiation is available. Here, we assessed ethanol effects on VGCC-dependent synaptic potentiation using whole cell patch-clamp recordings of alpha-amino-3-hydroxy-5-methyl-4-soxazolepropionic acid (AMPA) receptor-mediated miniature excitatory postsynaptic currents (mEPSCs) in area CA1 of the rat hippocampus. No potentiation was observed in artificial cerebrospinal fluid containing 2 to 3 mM Ca2+, but marked potentiation of mEPSCs was consistently observed in 4 mM Ca2+ and with patch pipettes containing an ATP-regenerating system. This potentiation was insensitive to the NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid, whereas it was completely blocked the L-type VGCC antagonist nifedipine. Potentiation was also blocked dose dependently by bath application of ethanol (25-75 mM), which had no effect on baseline mEPSC amplitude or frequency. The synaptic potentiation involved enhancement of both presynaptic and postsynaptic components because significant increases in both the frequency and amplitude of AMPA mEPSCs were observed. Ethanol inhibition of VGCC-dependent synaptic potentiation seemed to occur at the induction step because both the increases in mEPSC frequency and amplitude were affected. To address that question more directly, we used fluorescent imaging of synaptically evoked dendritic calcium events, which displayed a similarly marked ethanol sensitivity. Thus, ethanol modulates fast excitatory synaptic transmission by inhibiting the induction of an NMDA receptor-independent form of synaptic potentiation observed at excitatory synapses on central neurons.

Animals↗
PubMed2002

Observations of comet 19P/Borrelly by the miniature integrated camera and spectrometer aboard Deep Space 1.

The nucleus of the Jupiter-family comet 19P/Borrelly was closely observed by the Miniature Integrated Camera and Spectrometer aboard the Deep Space 1 spacecraft on 22 September 2001. The 8-kilometer-long body is highly variegated on a scale of 200 meters, exhibiting large albedo variations (0.01 to 0.03) and complex geologic relationships. Short-wavelength infrared spectra (1.3 to 2.6 micrometers) show a slope toward the red and a hot, dry surface (</=345 kelvin, with no trace of water ice or hydrated minerals), consistent with approximately 10% or less of the surface actively sublimating. Borrelly's coma exhibits two types of dust features: fans and highly collimated jets. At encounter, the near-nucleus coma was dominated by a prominent dust jet that resolved into at least three smaller jets emanating from a broad basin in the middle of the nucleus. Because the major dust jet remained fixed in orientation, it is evidently aligned near the rotation axis of the nucleus.

Carbon↗
PubMed1970

Strontium-90: effects of chronic ingestion on farrowing performance of miniature swine.

In experiments involving the ingestion of strontium-90 by nearly 800 female miniature swine and extending over three generations, no significant differences in litter size, percentage of stillborn, or birth weight were observed between controls and animals ingesting up to 625 microcuries of strontium-90 per day. At 625 microcuries per day, these animals were ingesting more than a million times the peak value of strontium-90 ever reported in the American diet. Animals on 3100 microcuries per day did not survive the gestation period. From these studies, it is evident that feeding levels of strontium-90 high enough to affect fetal or neonatal mortality in this species will not permit maternal survival long enough for the bearing of young.

Animals↗
PubMed1974

Miniature end plate potentials recorded from mammalian myoneural junction in vivo.

Fibers of the cat soleus muscle had a mean resting potential of 87 millivolts as measured with an intracellular microelectrode. Miniature end plate potentials had a mean amplitude of 0.95 millivolt, a mean frequency of 1.01 per second, a mean duration of 4.44 milliseconds, and a mean rate of rise of 0.99 volt per second. Two populations of response could be discerned on the basis of rate of rise. Neither alpha-chloralose nor nerve section had any significant effect on the response pattern. The in vivo preparation appears to provide a superior representation of the physiology of the myoneural junction.

Anesthesia↗
PubMed1985

Morphological novelty in the limb skeleton accompanies miniaturization in salamanders.

Salamanders of the genus Thorius (Plethodontidae) are among the smallest tetrapods. Hypotheses of limb skeletal evolution in these vertebrates were evaluated on the basis of estimates of natural variation, comparisons of skeletal homology, and analysis of molecular phylogeny. Nine carpal arrangements occur in Thorius, more than in all twelve related genera of typically larger salamanders; six of these arrangements are unique. They represent a trend toward a decrease in the number of separate cartilages that is independent of locomotor and ecological specialization. Miniaturization may be an important source of morphological novelty, distinct from local adaptation, in vertebrates.

Animals↗
PubMed1980

A Palladium-palladium oxide miniature pH electrode.

A wire-form miniature palladium-palladium oxide electrode has been fabricated for pH measurement. The electrode exhibits a super-Nernstian behavior and gives a mean pH response of 71.4 millivolts per [pH] (standard deviation, 5.2 millivolts). Uncorrected zero current potential values can be used to determine the pH value of the medium to within 0.012 pH. The electrode should find applications in biological, medical, and clinical studies.

Buffers↗
PubMed1978

Comparison of miniaturized multitest systems with conventional methodology for identification of Enterobacteriaceae from foods.

Four miniaturized multiple test systems were compared with tube methodology used to identify Enterobacteriaceae encountered in foods. Identification aids supplied with each system were used to assign names to isolates at the species level. For the 129 strains tested, the Minitek system demonstrated a 96.9 percent agreement with reactions in tubed media. The Inolex, Analytab, and PathoTec test systems exhibited 94.3, 93.8, and 92.7 percent agreement, respectively. Analytab identified 96.1 percent of the isolates to the species level, whereas the Minitek, PathoTec, and Inolex systems were able to identify 78.3, 32.6, and 27.1 percent, respectively. The results indicate that the Analytab and Minitek systems are acceptable substitutes for the tube methodology routinely employed in identifying enterics from foods. Although the PathoTec system might be used to screen isolates for their identity, neither the presently available PathoTec nor the Inolex systems should be substituted for current methodology when definitive identification of foodborne organisms is required.

Bacteriological Techniques↗
PubMed1976

Variability of the immunological state of germfree colostrum-deprived Minnesota miniature piglets.

Minnesota miniature piglets obtained by hysterectomy and deprived of colostrum were examined for the presence of immunoglobulin by immunoelectrophoresis, double-gel diffusion, and radial immunodiffusion techniques with specific anti-immunoglobulin chain sera. A large amount of variability existed between different litters of piglets and between different piglets within the same litter, ranging from no detectable immunoglobulin in the serum to very high immunoglobulin levels approaching that of the adult pig. All known classes of porcine immunoglobulin including immunoglobulin G, immunoglobulin M, and immunoglobulin A could be found in the sera from litters where there was extensive placental damage. This contaminating immunoglobulin was shown to have antibody activity to actinophage MSP-2 even when present in very low concentrations. The low level contamination with immunoglobulin G, which was the most frequently encountered type of contaminant, was demonstrated to be similar to sow immunoglobulin G both antigenically and in its molecular size. The data demonstrates that individual piglets must be tested for immunoglobulin content rather than being assumed to be immunologically "virgin" and emphasizes the need for an intact placenta barrier to obtain piglets free from maternal immunoglobulin and devoid of antigenic stimulation.

Animals↗
PubMed1979

Role of environment in the development of "natural" hemagglutinins in Minnesota miniature swine.

"Natural" hemagglutinin titers against a panel of fixed erythrocyte antigens were determined for groups of Minnesota miniature swine reared conventionally, in a specific pathogen-free facility, and in germfree isolators. Sera were assayed for hemagglutination (HA) titers by the microtiter method against 12 species of erythrocytes stabilized by treatment with pyruvic aldehyde and formaldehyde. These erythrocytes were stable for up to 2 years and gave slightly enhanced HA titers as compared to fresh, unfixed erythrocytes. Of the sera from conventional swine tested, the highest "natural" HA titers were directed towards rabbit, cat, swine dog, and burro erythrocytes (greater than 1:1,000), intermediate titers were detected against human A, B, and O, and sheep, pig, and chicken erythrocytes (1:64 to 1:1,000), whereas the lowest titers were found against ox and goat erythrocytes (less than 1:8). Titers obtained with sera from specific pathogen-free swine were 2- to 16-fold lower than those of conventional swine, but were of a similar distribution with regard to the species of erythrocyte tested. Germfree swine sera uniformly exhibited HA titers less than 1:4 against all species of erythrocytes. The majority of these hemagglutinins were immunoglobulin M class but there were some agglutinins of immunoglobulin A class and a slight amount of immunoglobulin G class. Specificity of these agglutinins was examined by absorption tests. The results are consistent with the hypothesis that natural hemagglutinins develop due to dietary or microbial antigenic stimulation, or both.

Agglutinins↗
PubMed2006

Structural organization and functional properties of miniature DNA insertion sequences in yersiniae.

YPALs (Yersinia palindromic sequences) are miniature DNA insertions scattered along the chromosomes of yersiniae. The spread of these intergenic repeats likely occurred via transposition, as suggested by the presence of target site duplications at their termini and the identification of syntenic chromosomal regions which differ in the presence/absence of YPAL DNA among Yersinia strains. YPALs tend to be inserted closely downstream from the stop codon of flanking genes, and many YPAL targets overlap rho-independent transcriptional terminator-like sequences. This peculiar pattern of insertion supports the hypothesis that most of these repeats are cotranscribed with upstream sequences into mRNAs. YPAL RNAs fold into stable hairpins which may modulate mRNA decay. Accordingly, we found that YPAL-positive transcripts accumulate in Yersinia enterocolitica cells at significantly higher levels than homologous transcripts lacking YPAL sequences in their 3' untranslated region.

Base Composition↗
PubMed1988

RAPIDEC UR, a 2-h miniaturized system for pinpointing uropathogens.

A miniaturized 2-h system (RAPIDEC UR; API System, la Balme-les-Grottes, Montalieu-Vercieu, France) that uses nine enzymatic tests for the diagnosis of most uropathogens was challenged with 330 strains. With few exceptions (Citrobacter, Enterobacter, and Providencia spp., Morganella morganii, and staphylococci other than Staphylococcus saprophyticus), there were distinct patterns that allowed at least a preliminary species diagnosis.

Bacteriological Techniques↗
PubMed1976

Modification of the Minitek Miniaturized Differentiation System for characterization of anaerobic bacteria.

The Minitek Miniaturized System (BBL) was modified for characterization of anaerobic bacteria. The modified system and the conventional Center for Disease Control method were used to test a variety of anaerobic bacteria, and results were compared. Tests performed by both techniques were indole and H2S production, esculin hydrolysis, nitrate reduction, and fermentation of glucose, mannitol, lactose, sucrose, maltose, salicin, glycerol, xylose, arabinose, mannose, rhamnose, and trehalose. The manufacturer's recommended procedure for the Minitek system was modified by using a new suspension medium (Lombard-Dowell broth) and an inoculum equivalent to the density of a McFarland no. 5 nephelometer standard. The Minitek results, recorded after 48 h, agreed satisfactorily with the conventional test results, usually recorded after 5 to 7 days of incubation. In the examination of 80 strains representing 22 different species or subspecies of anaerobic bacteria, with 16 biochemical tests performed in triplicate, 93.8% of the Minitek test results agreed with those of the corresponding conventional tests. Only tests for indole, H2S, and nitrate reduction gave less than 90% agreement. It was concluded that the modified Minitek system is a suitable substitute for the more expensive and time-consuming conventional procedure for determining carbohydrate fermentation and esculin hydrolysis by anaerobes. This system, when used in conjunction with other tests, can effectively aid in the definitive identification of commonly isolated anaerobes.

Anaerobiosis↗
PubMed1978

A miniature Wright peak-flow meter.

A new miniature Wright peak-flow meter has been designed and produced. The meter is tubular with a spring-loaded piston and a longitudinal slot through which air escapes. Its dynamic characteristics have been carefully designed to make it respond only to peak flow and not to rate of rise. Performance tests on early instruments showed fairly close correlation with the Wright peak-flow meter but with a constant error of + 38 1/min. On later models the correlation was increased to 0.990 and the error reduced to + 3%. The mini-meter correlates as well with the standard instrument as two standard instruments correlate with each other and should prove useful clinically.

Forced Expiratory Flow Rates↗