SEARCH · PubMed Health

Results for “interaction frequencies”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources

PubMed1998

The dependence of the distortion product 2f1-f2 on primary levels in non-impaired human ears.

The optimal intensity relation between the two primaries used to generate Distortion Product Otoacoustic Emissions (DPOAEs) in unimpaired human ears, over a clinically relevant intensity range, was evaluated using a commercially available clinical device. The ILO92 was used to determine the level of the DPOAE at 2f1-f2 for 16 combinations of primary levels in the range of 40 to 80 dB SPL from 40 unimpaired, young adult ears. Data were collected between 1 and 6 kHz at 1, 1.5, 2, 3, 4, 5, and 6 kHz. The commonly used procedure of dropping data points less than 3 dB above the noise floor was compared to a power subtraction procedure. A multivariate ANOVA was performed to determine main effects of gender, ear, stimulus levels, frequencies, and interactions between stimulus levels and frequencies. An overall increase of DPOAE amplitude with increase in primary level was observed, along with a decrease of the optimal difference in primary levels as L2 was increased. Although the power subtraction and 3-dB drop paradigms yielded similar results at high stimulus levels, the power subtraction paradigm provided a more realistic indicator of DPOAE level when low level primaries were used. Possible mechanisms responsible for the level dependence of the optimal relationship between primaries and implications for clinical choice of primary levels are discussed.

Acoustic Stimulation↗

PubMed2001

Seizure frequency affects event-related potentials (P300) in epilepsy.

To analyse the effect of epilepsy an P300 event-related potentials we studied 27 patients with idiopathic generalized epilepsy (IGE), 13 patients with temporal lobe epilepsy (TLE) and 60 normal controls. The prolongation of P300 latencies was highly cor related with increasing age in controls but not epileptic patients. The age-corrected P300 latency used in this study was actual P300 latency-predicted P300 latency (predicted P300 (msec)=306.20+0.79 age, P=0.001, R2=0.32). By using ANOVA analysis, the age-corrected latencies of P300 were significantly longer in TLE patients (19.72+/-47.82 msec, mean+/-SD) than in IGE patients (10.97+/-36.97 msec) and controls (0.23+/-20.28 msec). Likewise, significantly prolonged P300 latencies were seen in the epileptic patients with a seizure frequency more than 400 times (37.21+/-47.50 msec). The multivariate-adjusted odds ratio for those who had TLE was 10.97 (95% CI=3.99 - 30.14 ) in the prolonged latencies of P300 compared with that of IGE patients. The odds ratio of longer latencies of P300 was 7.43 (95% CI=2.75 - 20.08) among those who had a high seizure frequency (> or =400 times) compared with those who had a low seizure frequency. No interaction between TLE and high frequency of attacks was found. The age at onset of seizure and duration of illness was not associated with P300 latency prolongation. From the above results, we might infer that the seizure type of TLE and a high frequency of seizure are two major independent precipitate factors for abnormal latencies of P300 in the epileptic patients.

Adult↗

PubMed2000

Frequency and width crossing of two interacting resonances in a microwave cavity

Frequency and width crossing have been observed for two coupled resonances in a microwave cavity. The cavity consisted of two nearly identical rectangular boxes. The boxes were coupled by a slit of variable width. The data are well described by a non-Hermitean S matrix leading to a 2x2 non-Hermitean effective Hamiltonian. The values of the interaction strength |v| for which width crossing and frequency crossing, respectively, were observed, are above and below a critical value |v(c)| for which one expects a joint frequency and width crossing.

Journal Article↗

PubMed2003

Interaction between weak low frequency magnetic fields and cell membranes.

The question of whether very weak low frequency magnetic fields can affect biological systems, has attracted attention by many research groups for quite some time. Still, today, the theoretical possibility of such an interaction is often questioned and the site of interaction in the cell is unknown. In the present study, the influence of extremely low frequency (ELF) magnetic fields on the transport of Ca(2+) was studied in a biological system consisting of highly purified plasma membrane vesicles. We tested two quantum mechanical theoretical models that assume that biologically active ions can be bound to a channel protein and influence the opening state of the channel. Vesicles were exposed for 30 min at 32 degrees C and the calcium efflux was studied using radioactive (45)Ca as a tracer. Static magnetic fields ranging from 27 to 37 micro T and time varying magnetic fields with frequencies between 7 and 72 Hz and amplitudes between 13 and 114 micro T (peak) were used. We show that suitable combinations of static and time varying magnetic fields directly interact with the Ca(2+) channel protein in the cell membrane, and we could quantitatively confirm the model proposed by Blanchard.

Calcium↗

PubMed2005

Electrophysiological correlates of cortico-subcortical interaction: a cross-frequency spectral EEG analysis.

OBJECTIVE: Several studies have provided evidence for the notion that the coupling between slow and fast frequency in the EEG spectrum indicates cortico-subcortical cross-talk (CSC-ct). In addition, findings for increased limbic activation due to reduced cortical inhibition have recently been acquired. To get further insights into these mechanisms, the current study investigated whether CSC-ct would decrease as a function of increased slow (SW) or fast wave (FW) activity. METHODS: Resting state EEG recordings were obtained from 46 healthy, right-handed participants. CSC-ct was quantified by computing cross-frequency correlations between the power in the slow and fast frequency range. CSC-ct was compared between groups with relatively low and high SW activity and groups with relatively low and high FW activity. RESULTS: Relatively reduced SW, but not FW activity was associated with a significant coupling between slow and fast frequency EEG. Furthermore, relatively enhanced resting state SW activity was paralleled by slow and fast frequency EEG decoupling. CONCLUSIONS: These findings are in line with the notion that increased subcortical drive can go accompanied by reduced CSC-ct. SIGNIFICANCE: Cross-frequency EEG analyses might provide a unique approach to obtain novel insights into cortico-subcortical interactions in relation to affective and cognitive behavior.

Adolescent↗

PubMed1982

Electronic distributions within protein phenylalanine aromatic rings are reflected by the three-dimensional oxygen atom environments.

The atomic environments of 170 phenylalanine-residue aromatic rings from 28 protein crystal structures are transformed into a common orientation and combined to calculate an average three-dimensional environment. The spatial distribution of atom types in this environment reveals a preferred interaction between oxygen atoms and the edge of the planar aromatic rings. From the difference in frequency of interaction of oxygen atoms with the edge and the top of the ring, an apparent net free energy difference of interaction favoring the edge of the ring is estimated to be about -1 kcal/mol (1 cal = 4.184 J). Ab initio quantum mechanical calculations, performed on a model consisting of benzene and formamide, indicate that the observed geometry is stabilized by a favorable enthalpic interaction. Although benzene rings are considered to be nonpolar, the electron distribution is a complex multipole with no net dipole moment. The observed interaction orientation frequencies demonstrate that these multipolar electron distributions, when occurring at the short distances encountered in densely packed protein molecules, are significant determinants of internal packing geometries.

Benzene↗

PubMed2004

Nonbreeding season pairing behavior and the annual cycle of testosterone in male and female downy woodpeckers, Picoides pubescens.

Studies in birds show that testosterone (T) concentrations vary over the annual cycle depending on mating system and life history traits. Socially monogamous species show pairing behavior throughout the year and low levels of male-male aggression and are underrepresented in these studies, yet the function of testosterone could be particularly important for sexual and social interactions occurring outside the breeding season. We measured fecal T concentrations over the annual cycle and the frequency of interactions between male and female downy woodpeckers (Picoides pubescens) from late fall through early spring. We validated the fecal assay by collecting blood in conjunction with a subsample of our fecal samples: fecal T correlated with circulating levels in the blood. The annual peak level of T in males was relatively low and short-lived, similar to that of other bird species with low levels of male-male aggression and high paternal care. The annual cycle of female T resembled the male pattern, and the ratio of male T to female T was close to 1.0. Likewise, the frequency of aggression among females was similar to the frequency among males. Overall, testosterone levels in both sexes were variable, even in winter. In other bird species, sexual behavior during nonbreeding periods correlates with circulating levels of T in males. Based on this observation, we tested the hypothesis that T in winter was positively related to the frequency of interaction between mated downy woodpeckers. The results showed no such relationship. We discuss this finding and further relate the annual cycle of T in both males and females to behaviors that appear to facilitate mate choice and retention of the pair bond during conspecific challenge.

Animals↗

PubMed1989

Interactions between heat-induced chiasma frequency changes in Schistocerca gregaria.

Using inbred laboratory stocks of the locust Schistocerca gregaria, two experiments were carried out using composite heat-treatment programmes of 40 degrees C and 30 degrees C combinations. These were designed to superimpose different heat-induced increases and decreases in chiasma frequency, to determine what interactions would occur and which effects might be dominant. It was found that both of the heat-induced decreases in chiasma frequency which can be obtained (Effects 2 and 3), were dominant over both of the different types of increase (Effects 1 and 4), with the largest decrease (Effect 3) being dominant over all others.

Animals↗

PubMed1975

Temporal frequency characteristics of spatial interaction in human vision.

In psychophyscial experiments the bright-dark contrast effects observed in a steady test-field were measured as a function of the temporal frequency of an inducing-field modulated symmetrically about the test-field luminance. The frequency-contrast functions obtained from these measurements were interpreted as reflecting the temporal frequency characteristics of the lateral pathways within the B and D systems (the on-center and off-center neurons) in human vision. Psychophysical evidence is further presented that the lateral neural pathways have lower temporal cut-off frequencies than the "straight-through" pathways. The results are discussed in terms of the frequency characteristics of the center and surround of the receptive fields of on-center and off-center neurons. It is doubtful, however, whether the psychophysical results can be fully explained by the properties of the single-unit receptive field mechanisms.

Humans↗

PubMed1980

Relative frequency effect on choice reaction time.

Subjects gave either vocal (position-naming) or manual (button-press) responses to spatially arrayed lights in a four-alternative choice reaction task. Relative stimulus frequency, stimulus discriminability, and S-R compatibility were each shown to be significant determinants of RT. The effects of discriminability and compatibility on the mean and variance of RT were additive. A significant interaction of frequency X discriminability was taken as evidence that a component of the relative frequency effect arises at the stimulus encoding stage. A second component of the relative frequency effect, presumed to occur at the S-R translation stage, was indicated by a significant interaction of frequency X compatibility. It was proposed that recall of the S-R translation rule takes longer for less frequent stimuli and that this difference increases when S-R pairings are not compatible.

Adult↗

PubMed1987

Social network characteristics and psychological well-being: a replication and extension.

This article represents a replication and extension of a previous study by Israel and her colleagues that investigated the relationship between psychological well-being and social network characteristics. The present research included both a comparable sample of white women (N = 104) between the ages of 60 and 68 (as in the original study), and a more extensive adult population of men and women (N = 718) between the ages of 50 and 95. The network characteristics examined are categorized along three broad dimensions: Structure--linkages in the overall network (size and density); interaction--nature of the linkages themselves (frequency, geographic dispersion, and reciprocity); and functions that networks provide (affective support and instrumental support). The results indicate a predominance of comparable findings for both the replication and extension studies. Of the eight network characteristics examined, the results of five of the regression analyses were the same across all three studies. The network characteristics of size, density, geographic dispersion, reciprocal instrumental support, and instrumental support did not make a significant contribution to the variance in psychological well-being. Of the other three network characteristics, the effect of frequency of interaction varied across the studies, and a pattern of significant results was found for affective support and reciprocal affective support. A discussion of this evidence in light of current literature and implications for practice and research is included.

Aged↗

PubMed1992

The chemical shift interaction under weak radio frequency pulses.

The chemical shift anisotropy of a nuclear spin system in a strong magnetic field can be comparable to the strength of the rf pulse (weak pulse condition). In this case, the commonly used assumption that the chemical shift interaction Hamiltonian in the duration of a rf pulse can be neglected is no longer effective. The rf response characteristics of a spin-1/2 system under a weak pulse condition is studied in detail. The relationships between the distortion of the chemical shift powder spectrum and the relative rf field amplitude under various conditions are given. The suppression of sidebands of a MAS spectrum is analysed as an example of solid multiple pulse experiments. The experimental results are in good agreement with computer simulations.

Alanine↗

PubMedDate not supplied

[The frequency spectrum in the interaction between continuous and impulse noise: an anatomic functional evaluation].

In industrial setting impulse noise rarely occurs in isolation. Impulses are more often superimposed on a background of continuous noise. Since measurement of peak sound pressure level or energy considerations may not provide a sufficient index of danger to hearing, examining the frequency spectra of the noises appeared to be important. Seven groups of five chinchillas were used in this study. Four groups were exposed to octave bands of noise centered at 0.5, 2 or 4 kHz having intensities of 95, 90 and 86 dB SPL respectively or impulse noise of 113 dB peak SPL applied on time per 1 second. Three groups were exposed to the combination of impulse noise and one of the above continuous noises. Each exposure lasted five days. PTS was calculated on each animal using auditory evoked potentials. The cochleas were dissected and evaluated using conventional histological surface preparation and examined with scanning electron microscopy (SEM) employing a JEOL 35 microscope. The groups exposed to only the impulse or to continuous noise alone developed neither PTS nor hair cell loss. Considerable values of PTS and sensory cell loss were observed in animals exposed to impulse noise in combination with 2 and 4 kHz of continuous noise. This interaction effect increases as the spectral overlapping between the impulse and continuous noise increases. In these animals excellent information concerning the sensory cell losses or cell damage was obtained with SEM. The results of the present study demonstrate that interaction between impulse and continuous noise can indicate increased hazard, which is highly dependent not only upon the total energy of the complex exposure but also on the degree of spectral overlapping between impulse and continuous noise.

Animals↗

PubMed1994

Fluoroquinolones: use of clinical data to aid formulary choice by the system of objective judgement analysis (SOJA) method.

Fluoroquinolones are used in many hospitals for the treatment of complicated urinary tract infections, gastrointestinal infections, hospital acquired pneumonia and osteomyelitis. A review of the fluoroquinolones by the System of Objective Judgement Analysis (SOJA) method is presented. The following selection criteria were involved in the study: the number of registered indications, the number of dosage forms, the ratio between the area under the plasma concentration-time curve (AUC) and the minimum inhibitory concentration for 90% of strains (MIC 90), variability of the oral bioavailability, drug interactions, dosage frequency, equal dosage for oral and parenteral use, development of resistance, clinical efficacy, adverse events, cost and documentation. Both the oral and the parenteral formulation were included in the study. Ofloxacin shows the highest score, mostly because of the lower incidence of drug interactions, dosage frequency, cost and (relative to ciprofloxacin) a similar dosage for oral and parenteral use. Ciprofloxacin is the best documented drug. Pefloxacin shows the lowest SOJA score. Users of this method are free to determine the relative weight of the various selection criteria that they consider to be correct, although some of the criteria are internationally valid.

Administration, Oral↗

PubMed1995

ORC and Cdc6p interact and determine the frequency of initiation of DNA replication in the genome.

The origin recognition complex (ORC) binds replicators in the yeast S. cerevisiae in a manner consistent with it being an initiator protein for DNA replication. Two-dimensional (2D) gel techniques were used to examine directly initiation of chromosomal DNA replication in temperature-sensitive orc mutants. Unlike in wild-type cells, in orc2-1 and orc5-1 mutant cells, only a subset of replicators formed active origins of DNA replication at the permissive temperature. At the restrictive temperature, the number of active replicators was diminished further. Using a genetic screen, CDC6 was identified as a multicopy suppressor of orc5-1. 2D gel and biochemical analyses demonstrated that Cdc6p interacted functionally and physically with ORC. We suggest that ORC and Cdc6p form a prereplication complex at individual replicators and therefore cooperate to determine the frequency of initiation of DNA replication in the genome.

Cell Cycle Proteins↗

PubMed2003

A simple measure of correlation across time, frequency and space between continuous brain signals.

This paper introduces a simple but systematic method to estimate correlations between the spectral energy of two continuous electrophysiological signals in such a way that it can detect relationships between different frequencies and different latencies. From two series of signals (e.g. electroencephalogram, magnetoencephalogram or local field potentials) recorded from two sites in response to repeated sensory stimulations, the method computes the time-frequency energy of each signal. Then, it computes the Spearman rank order correlation coefficient across all the trials between the energy of the first signal series in one time-frequency region and the energy of the second signal series in a second time-frequency region. The method was designed to analyze interactions between frequency bands, in an effort to describe how the main brain rhythms interact with each other across time and space. It was applied to two simulations and to intracranial electro-encephalogram (EEG) recordings obtained from an epileptic patient performing two verbal discrimination tests (a phonological and a semantic task). It led to the identification of different correlations patterns in the gamma band depending on the level of semantic analysis performed by the patient.

Brain↗

PubMed1995

Tests of attentional flexibility in listening to polyrhythmic patterns.

Four experiments examined attentional flexibility in listening to polyrhythmic patterns. Musically trained and untrained listeners detected changes in timing of 1 tone (the lower tone) in a 3:2 polyrhythm in which high and low tones varied in frequency separation. Experiment 1 encouraged integrative attending; all listeners performed significantly poorer in conditions with wide as opposed to narrow frequency separations. Experiment 2, which encouraged selective attending to low tones, reversed these results: Performance was poorer in the narrow frequency conditions. In neither experiment did skill interact with frequency separation. Experiments 3 and 4 extended these findings to moderate frequency separations. Over all experiments, musically trained listeners exhibited an enhanced ability to detect timing variations, but not flexibility of perceptual organization as it applies to detection of timing changes. Instead, pattern structure (e.g., frequency and time relation) decisively influenced perception for both levels of skill.

Attention↗

PubMedDate not supplied

Effect of stimulus duration on stapedius reflex threshold in electrical stimulation via cochlear implant.

The effect of stimulus duration on the threshold of the contralateral stapedius reflex was investigated in patients supplied with a Vienna cochlear implant (analog stimulation via CI) and compared to results of a normal-hearing reference group in case of acoustic stimulation. Changes in reflex threshold were determined at four frequencies (125, 500, 1,000 and 2,000 Hz in case of electrostimulation and at 500, 1,000, 2,000 and 4,000 Hz for acoustic stimulation) and for five durations (30, 50, 100, 300 and 500 ms). The comparison of the two stimulation modes was accomplished by using the same instrumentation and procedure. Reflex threshold was evaluated according to an objective criterion based on the individual noise distribution of recordings without reflex and by subjective judgement. For both stimulation modes a strong effect of stimulus duration on reflex threshold was observed (p < 0.001). The amount of temporal integration reflected by the threshold difference between 500 and 50 ms was approximately 2-4 dB for electrical stimulation via CI and 6 dB for acoustic stimulation in normal-hearing individuals. In case of electrostimulation, the reflex threshold for stimuli of 30 ms was most often above the limit of uncomfortable loudness sensation; the increase in reflex threshold for acoustic stimulation between 500 and 30 ms was approximately 14 dB. There was no evidence of frequency effect on reflex threshold nor an interaction between frequency and stimulus duration for either stimulation mode.

Adult↗