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PubMedDate not supplied

Two-dimensional color Doppler estimation of the severity of atrioventricular valve regurgitation: important effects of instrument gain setting, pulse repetition frequency, and carrier frequency.

Literature reports of good correlation between two-dimensional color Doppler and ventriculography for estimation of the severity of atrioventricular valve regurgitation have appeared. Local experience has been variable. The purpose of this study was to evaluate three factors for their effect on two-dimensional color Doppler display of the apparent area of regurgitant flow. The factors studied were instrument gain setting, pulse repetition frequency (PRF), and carrier frequency. Sixteen regurgitant valves were examined with high quality commercial instrumentation from two manufacturers. Electrocardiographic-triggered image gating was used for recording and planimetry of maximal imaged flow area (IFA). Examinations were performed at two gain settings with constant carrier frequency and PRF, at three carrier frequencies (2.5, 3.5, and 5 MHz) at constant gain, and at differing PRF (3.0 to 12 kHz). Reduction in gain setting made little difference in asthetic quality of regurgitant jets, but their areas decreased by 29%. Carrier frequency was found to greatly affect IFA, with each higher carrier frequency giving significantly smaller IFAs. PRF also affected IFA consistently, with progressively smaller IFAs at each higher PRF. There was no useful correlation between IFA of a single jet evaluated on the two instruments at generally similar settings. It is concluded that instrument gain setting, PRF, and carrier frequency each significantly affects the size of IFA within a single instrument and between different instruments. Given the variety of instruments and settings employed within the cardiology community, it is unlikely that even moderately accurate grading of severity of regurgitation based on IFA can be done unless instrument settings are specified and standardized. There is a clear need for annotation of instrument settings during color Doppler examinations and a need for concensus regarding "optimal" settings. Finally, the consistency of reduction in IFA with increasing carrier frequency and PRF within each of the instruments tested suggests investigation of "normalization" of IFA displays.

Adolescent↗

PubMed2001

Effects of frequency-shifted auditory feedback on fundamental frequency of long stressed and unstressed syllables.

Twenty-four normally speaking subjects had to utter the test word /tatatas/ with different stress patterns repeatedly. Auditory feedback was provided by head-phones and was shifted downwards in frequency during randomly selected trials while the subjects were speaking the complete test word. If the first syllable was long stressed, fundamental frequency of the vowel significantly increased by 2 Hz (corresponding to 25.5 cents) under frequency-shifted auditory feedback of .5 octave downwards, whereas under a shift of one semitone downwards a trend of an increase could be observed. If the first syllable was unstressed, fundamental frequency remained unaffected. Regarding the second syllable, significant increases or a trend for an increase of fundamental frequency was found in both shifting conditions. Results indicate a negative feedback mechanism that controls the fundamental frequency via auditory feedback in speech production. However, within a syllable a response could be found only if the syllable duration was long enough. Compensation for frequency-shifted auditory feedback still is quite imperfect. It is concluded that control of fundamental frequency is rather important on a suprasegmental level.

Adult↗

PubMed1981

Frequency of thermostability variants: estimation of total "rare" variant frequency in human populations.

Eight erythrocyte enzymes were examined for thermostability in an unselected sample of 100 newborn infants. Three thermolabile variants, one each of lactate dehydrogenase, glucosephosphate isomerase, and glucose-6-phosphate dehydrogenase, were identified, none of which was detectable as a variant by standard electrophoretic techniques. All were inherited. This frequency of 3.8 heritable thermostabiliy variants per 1000 determinations is to be compared with a frequency of electrophoretically detectable variants of 1.1 per 1000 determinations, a frequency of 2.4 enzyme-deficiency variants per 1000 determinations, and a frequency of 1.1 hypo/hyperactive enzyme-activity variants per 1000 determinations in this human newborn population. The total measured frequency of individuals with rare enzyme deficiency or electrophoretic or thermostability (or both) variants at these loci is 8.3 per 1000 determinations. A similar distribution and frequency is seen when the comparison is limited to the seven loci studied by all techniques. It is clear that not all of the electrophoretic and thermostability variants present in the population are detected by the techniques used in this study. Accordingly, it is estimated that the true frequency of carriers of a rare variant for each of these enzyme-coding loci averages greater than 10/1000. Some implications of these frequencies for human disease are discussed.

Adult↗

PubMed2004

Time-frequency based newborn EEG seizure detection using low and high frequency signatures.

The nonstationary and multicomponent nature of newborn EEG seizures tend to increase the complexity of the seizure detection problem. In dealing with this type of problem, time-frequency based techniques were shown to outperform classical techniques. Neonatal EEG seizures have signatures in both low frequency (lower than 10 Hz) and high frequency (higher than 70 Hz) areas. Seizure detection techniques have been proposed that concentrate on either low frequency or high frequency signatures of seizures. They, however, tend to miss seizures that reveal themselves only in one of the frequency areas. To overcome this problem, we propose a detection method that uses time-frequency seizure features extracted from both low and high frequency areas. Results of applying the proposed method on five newborn EEGs are very encouraging.

Diagnosis, Differential↗

PubMed1991

Sister chromatid exchange frequency in Hodgkin's disease patients with elevated in vivo hprt mutant frequencies.

The frequency of sister chromatid exchanges (SCEs) was determined in Hodgkin's disease (HD) patients prior to therapy, following radiotherapy, and following combined radiotherapy and chemotherapy. The frequency of hprt- mutants in these patients has been reported previously. The frequency of SCEs and hprt- mutants in the same individuals were compared. In non-HD controls the mean SCE frequency and the mean of high SCE frequency cells (HFCs) were significantly increased by smoking, while mutant frequency (MF) showed no effect. Untreated HD patients had mean SCEs, mean HFCs and mean MFs that were higher than non-MD controls. In treated patients, mean SCE and HFC frequencies were lower than untreated patients and non-HD controls, while their MFs were significantly elevated. Overall, SCE frequency was not correlated with MF in control or HD patient groups, suggesting that these biomarkers may reflect, in this case, fundamental biological differences between these processes.

Adolescent↗

PubMed1994

Radio frequency currents induced in the human body for medium-frequency/high-frequency broadcast antennas.

Radio frequency currents in the human body, induced by high-frequency and medium-frequency high-power broadcast antennas, were studied theoretically and experimentally. An analytical formula was derived to calculate the foot currents in a grounded semispheroidal model of the human body. The model agrees within 30% with the results given by the standard formula presented by Gandhi on the basis of measurements with humans. Near 100 kHz, the model predicts a decrease of 14% of the current dissipated in the human body, which is due to the beta relaxation of the cells. The effect of the body and foot-contact impedances were studied with the aid of a simplified equivalent circuit which showed that the body impedance does not considerably affect the foot current below 10 MHz. The normalized foot currents measured in front of the broadcast antennas were within 30% agreement of the currents calculated with the Gandhi formula from the electric fields measured at a height of 1 m. The foot currents are induced by vertical electric fields for both medium-frequency and high-frequency antennas in spite of a strong horizontal component in the latter case. The distance at which the occupational exposure limit of 200 mA was exceeded in the worst (maximum coupling) case was 50 m for the high-frequency antenna and < 14 m for the medium-frequency antenna. In the latter case, the radio frequency shocks resulting from touching ungrounded metallic bodies impose a practical limit to about 40 m.

Electromagnetic Fields↗

PubMed2006

The right information may matter more than frequency-place alignment: simulations of frequency-aligned and upward shifting cochlear implant processors for a shallow electrode array insertion.

OBJECTIVE: It has been claimed that speech recognition with a cochlear implant is dependent on the correct frequency alignment of analysis bands in the speech processor with characteristic frequencies (CFs) at electrode locations. However, the use of filters aligned in frequency to a relatively basal electrode array position leads to significant loss of lower frequency speech information. This study uses an acoustic simulation to compare two approaches to the matching of speech processor filters to an electrode array having a relatively shallow depth within the typical range, such that the most apical element is at a CF of 1851 Hz. Two noise-excited vocoder speech processors are compared, one with CF-matched filters, and one with filters matched to CFs at basilar membrane locations 6 mm more apical than electrode locations. DESIGN: An extended crossover training design examined pre- and post-training performance in the identification of vowels and words in sentences for both processors. Subjects received about 3 hours of training with each processor in turn. RESULTS: Training improved performance with both processors, but training effects were greater for the shifted processor. For a male talker, the shifted processor led to higher post-training scores than the frequency-aligned processor with both vowels and sentences. For a female talker, post-training vowel scores did not differ significantly between processors, whereas sentence scores were higher with the frequency-aligned processor. CONCLUSIONS: Even for a shallow electrode insertion, we conclude that a speech processor should represent information from important frequency regions below 1 kHz and that the possible cost of frequency misalignment can be significantly reduced with listening experience.

Adult↗

PubMed2005

Instantaneous frequency decomposition: an application to spectrally sparse sounds with fast frequency modulations.

Classical time-frequency analysis is based on the amplitude responses of bandpass filters, discarding phase information. Instantaneous frequency analysis, in contrast, is based on the derivatives of these phases. This method of frequency calculation is of interest for its high precision and for reasons of similarity to cochlear encoding of sound. This article describes a methodology for high resolution analysis of sparse sounds, based on instantaneous frequencies. In this method, a comparison between tonotopic and instantaneous frequency information is introduced to select filter positions that are well matched to the signal. Second, a cross-check that compares frequency estimates from neighboring channels is used to optimize filter bandwidth, and to signal the quality of the analysis. These cross-checks lead to an optimal time-frequency representation without requiring any prior information about the signal. When applied to a signal that is sufficiently sparse, the method decomposes the signal into separate time-frequency contours that are tracked with high precision. Alternatively, if the signal is spectrally too dense, neighboring channels generate inconsistent estimates-a feature that allows the method to assess its own validity in particular contexts. Similar optimization principles may be present in cochlear encoding.

Acoustics↗

PubMed1990

Binaural masking experiments using noise maskers with frequency-dependent interaural phase differences. II: Influence of frequency and interaural-phase uncertainty.

This study investigates whether binaural signal detection is improved by the listener's previous knowledge about the interaural phase relations of masker and test signal. Binaural masked thresholds were measured for a 500-ms dichotic noise masker that had an interaural phase difference of 0 below 500 Hz and of pi above 500 Hz. The thresholds for two difference 20-ms test signals were determined within the same measurement using an interleaved adaptive 3-interval forced-choice (3IFC) procedure. In each 3IFC trial, both signals could occur with equal probability (uncertainty). The two signals differed in frequency and interaural phase in such a way that one signal always had a frequency above the masker edge frequency (500 Hz) and no interaural phase difference (So), whereas the other signal frequency was below 500 Hz and the interaural phase difference was pi (S pi). The frequencies of a signal pair remained fixed during the whole 3IFC track. These two signals thus lead to two different binaural conditions, i.e., NoS pi for the low-frequency signal and N pi So for the high-frequency signal. For comparison, binaural masked thresholds were measured with the same masker for fixed signal frequency and phase. The binaural masking level differences (BMLDs) resulting from the two experimental conditions show no significant difference. This indicates that the binaural system is able to apply different internal transformations or processing strategies simultaneously in different critical bands and even within the same critical band.

Attention↗

PubMed1997

Apparent and real recombination frequencies in multicopy plasmids: the need for a novel approach in frequency determination.

Recombination studies of bacteria are often carried out with multicopy plasmids, and recombination frequencies are often deduced from the proportion of cells in the population that express a recombinant phenotype. These frequencies should however be called apparent frequencies, since detection of the recombinant cells requires not only the formation of a rearranged plasmid but also its establishment in the cell. The establishment of the recombinant plasmid can possibly be affected by its interaction with the parental plasmids. To test this hypothesis, we have used a plasmid system enabling the study of deletion formation between short direct repeats (18 bp) in Bacillus subtilis and developed a method by which deletion frequencies are measured under conditions under which interaction is abolished. Real deletion frequencies were thus determined and compared with apparent deletion frequencies. Real frequencies were underestimated by a factor ranging from 4- to 500-fold, depending upon the plasmid under study. This implies that a large majority of the recombinant molecules that are formed are generally not detected. We show that apparent deletion frequencies strongly depend upon (i) the parental plasmid copy number, (ii) the ability of the recombinant molecules to form heterodimeric plasmids, and (iii) the fitness of the recombinant molecules relative to that of parental molecules. Finally, we show that under conditions under which all recombinant molecules are scored, transcription can inhibit the deletion process 10-fold.

Bacillus subtilis↗

PubMed2005

Active and passive frequency stabilization for a Q-switched Z-fold radio-frequency-excited waveguide CO2 laser with two channels.

We report on passive offset frequency stability in free-running applications and active offset frequency stability achieved by use of a frequency-locking technique for a Q-switched Z-fold rf-excited waveguide CO2 laser with two channels. The laser structure of common electrodes and two channels has the advantage of compensating for the frequency variation caused by variations in temperature, cavity length, gas refractive index, and mechanical vibrations, so its offset frequency stability is higher than that of two separate lasers. In the experiments, the offset frequency shift was less than 6 MHz for 3 min in free-running mode. The technique of active offset frequency locking by counting was also introduced. The beat frequency shifting value was smaller than +/- 0.5 MHz in the long-term.

Journal Article↗

PubMed2003

Broad-spectrum frequency comb generation and carrier-envelope offset frequency measurement by second-harmonic generation of a mode-locked fiber laser.

A frequency comb spanning more than one octave has been achieved by injecting the second-harmonic generation (780 nm) of a mode-locked fiber laser (1.56 microm) into a photonic crystal fiber. We propose and realize a novel interferometric scheme for observing the carrier-envelope offset frequency of the frequency comb. Frequency noise has been observed on the measured carrier-envelope offset frequency, which has been confirmed to be generated in the photonic crystal fiber by comparing the measured beat frequencies between cw lasers and frequency combs before and after the photonic crystal fiber. The mode-locked fiber laser is considered to be an important candidate for the light source used in realizing a compact optical frequency measurement system including applications in the telecommunication bands.

Journal Article↗

PubMed2006

Sweep optical frequency synthesizer with a distributed-Bragg-reflector laser injection locked by a single component of an optical frequency comb.

A sweep optical frequency synthesizer is demonstrated by using a frequency-stabilized optical frequency comb and injection-locked distributed-Bragg-reflector (DBR) laser diode. The injection-locked DBR laser acts as a single-frequency filter and, simultaneously, a high-gain amplifier of the optical frequency comb. The frequency instability of the heterodyne beat signal between two independently injection-locked DBR lasers is measured to be 2.3 x 10(-16) at 1 s averaging time. The output frequency of the sweep optical frequency synthesizer can be precisely tuned over 1 GHz, and a saturated absorption spectrum of the Cs D2 line at 852 nm is recorded by the injected DBR laser.

Journal Article↗

PubMed2006

Recursive reminding: effects of repetition, printed frequency, connectivity, and set size on recognition and judgments of frequency.

In the present experiments, predictions of common path and recursive-reminding models of recognition (RG) and judgments of frequency (JOFs) were contrasted. The results indicated that each task is affected by study frequency, printed frequency, and associative connectivity. However, effect size analyses indicated that study frequency and item attributes show a double dissociation over tasks. Study frequency has a greater effect on JOFs than on RG, whereas printed frequency and associative connectivity have greater effects on RG than on JOFs. The recursive-reminding model predicts differential effects of study frequency, because it assumes that although both tasks are influenced by familiarity, JOF is more likely to be affected by recollective reminding as a procedure for encoding event frequency. Associative set size effects were absent in each task, suggesting that competitors play no role in either task.

Association Learning↗

PubMed2003

[Effect of peritonitis frequency on the effectiveness of peritoneal dialysis and effect of peritoneal dialysis effectiveness on the frequency of peritonitis].

UNLABELLED: Peritonitis is the most serious complication of peritoneal dialysis treatment for ESRD. There is no unanimous attitude yet concerning the influence of PD adequacy on the frequency of peritonitis. PATIENTS: The paper reports on a study of interrelation of peritonitis frequency and PD adequacy in 61 patients (27 women, 34 men) during a 5-year period. The group included 88% of all PD patients (61 of totally 69). RESULTS AND DISCUSSION: The patients experienced a total of 71 peritonitis episodes over a total of 1615 months of PD treatment. There was one peritonitis episode per 23 months of treatment on an average. When a patient who experienced 11 peritonitis episodes was excluded, the average frequency of peritonitis turned to one in 26 months. Peritonitis frequency and PD adequacy showed a significant negative correlation (r = 0.25, p < 0.05). PD adequacy expressed as total weekly Kt/V did not differ between the patients with and those without a history of peritonitis (Kt/V+ = 1.87 +/- 0.21, Kt/V- = 1.88 +/- 0.24; t = 0.17, p > 0.05). The frequency of peritonitis in men was twofold that in women, i.e. one peritonitis in every 17.24 +/- 11.67 months of treatment in men, and one peritonitis in every 37.81 +/- 13.11 months in women. The difference was statistically significant (t = 6.39, p < 0.01). However, PD adequacy did not differ between men and women (Kt/V = 1.84 +/- 0.21: 1.92 +/- 0.23, t = 1.40, p > 0.05). Patients with more adequate dialysis (n = 51) (Kt/V = 1.70) had one peritonitis in every 23.16 +/- 20.07 months on an average, and those with less adequate dialysis one peritonitis in 21.82 +/- 18.12 months of treatment. The difference was not statistically significant (t = 0.21, p > 0.05). The patients in whom PD was the first method of ESRD treatment (n = 55) experienced one peritonitis in every 24.04 +/- 12.51 months of treatment on an average, and those in whom PD was the second method of ESRD treatment (n = 6) had one peritonitis in 15.68 +/- 13.54 months of treatment. The difference was not significant (t = 1.45, p > 0.05). The difference in dialysis adequacy between these two groups was not significant either, even though the patients with PD as the first method had more adequate dialysis (1.88 +/- 0.22: 1.83 +/- 0.27; t = 0.44, p > 0.05). CONCLUSION: Peritonitis frequency and PD adequacy are significantly negatively correlated. The patients with higher peritonitis frequency had less adequate dialysis, while the patients with less adequate dialysis had peritonitis more frequently. However, the patients with a history of peritonitis had not significantly less adequate dialysis, nor the patients with less adequate dialysis had a significantly higher frequency of peritonitis.

Adult↗

PubMed1991

Acute airway injury during high-frequency jet ventilation and high-frequency oscillatory ventilation.

BACKGROUND AND METHODS: We compared tracheal histologic injury patterns, airway pressure (Paw) requirements, and in vivo and in vitro estimate of airway humidification in 13 adult cats with normal lungs mechanically ventilated for 16 hr. Six animals were treated with high-frequency jet ventilation at 400 breaths/min and seven animals with high-frequency oscillatory ventilation at 900 breaths/min. RESULTS: Peak airway pressure, Paw, mean Paw, and end-expiratory pressure requirements were significantly higher for high-frequency oscillatory ventilation as compared with high-frequency jet ventilation for similar gas exchange (p less than .01). While in vivo estimates of airway humidification suggested progressively greater H2O delivery into the respirator circuit, and therefore the airway, with higher frequencies, the in vitro study suggested similar relative humidities of the delivered gases during both types of mechanical ventilation. Tracheal injury, measured using a semiquantitative scoring system, was scored similarly for both ventilators studied despite the higher pressure requirements seen with the high-frequency oscillator. CONCLUSIONS: In this animal model, high-frequency ventilation using either jet or oscillation techniques produced similar inflammatory tracheal damage despite differences in Paw exposure and humidity.

Air Pressure↗

PubMed1980

Oscillations of frequency in Batesian mimics, hawks and doves, and other simple frequency dependent polymorphisms.

It is customary to infer the properties of the internal equilibria produced by frequency dependent selection from the properties of the boundary equilibria (often called the "invasion" criterion). This paper demonstrates that there are some circumstances that there is a truly stable, unique, internal equilibrium. For two alleles with complete dominance, if phenotype fitness declines monotonically with increasing frequency, then the internal point of equal phenotype fitness is the unique internal equilibrium of the genes, and is not unstable; this criterion may also be met if the fitness of one phenotype increases with frequency. It must be truly stable, in the sense of not producing oscillations, if the decline of fitness is linear or convex upwards and no phenotype is lethal at any frequency; the hawk-dove game complies with both conditions, and at least the second condition is likely to be met in most of the models encountered in sociobiology. However, an equilibrium which induces damped oscillations, or perhaps even complex limit cycles, is possible if at least one phenotype can be lethal at high frequency, or if the decline in fitness is strongly curvilinear and concave upwards. One case of curvilinear frequency dependence, a dimorphic batesian mimic with a non-mimetic form, is examined in detail. Although oscillations about the recessive or Y-linked, this will only occur when selection coefficients are very large, and (except for Y-linkage) only if both sexes can be mimetic. As selection is density as well as frequency dependent, such conditions may be produced in the real world by large fluctuations in population size.

Adaptation, Biological↗

PubMed2005

The evolution of resource specialization through frequency-dependent and frequency-independent mechanisms.

Levins's fitness set approach has shaped the intuition of many evolutionary ecologists about resource specialization: if the set of possible phenotypes is convex, a generalist is favored, while either of the two specialists is predicted for concave phenotype sets. An important aspect of Levins's approach is that it explicitly excludes frequency-dependent selection. Frequency dependence emerged in a series of models that studied the degree of character displacement of two consumers coexisting on two resources. Surprisingly, the evolutionary dynamics of a single consumer type under frequency dependence has not been studied in detail. We analyze a model of one evolving consumer feeding on two resources and show that, depending on the trait considered to be subject to evolutionary change, selection is either frequency independent or frequency dependent. This difference is explained by the effects different foraging traits have on the consumer-resource interactions. If selection is frequency dependent, then the population can become dimorphic through evolutionary branching at the trait value of the generalist. Those traits with frequency-independent selection, however, do indeed follow the predictions based on Levins's fitness set approach. This dichotomy in the evolutionary dynamics of traits involved in the same foraging process was not previously recognized.

Conservation of Natural Resources↗