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 127 records · Page 7Linked to original sources

PubMed2000

Characterization of sleep spindles using higher order statistics and spectra.

This work characterizes the dynamics of sleep spindles, observed in electroencephalogram (EEG) recorded from humans during sleep, using both time and frequency domain methods which depend on higher order statistics and spectra. The time domain method combines the use of second- and third-order correlations to reveal information on the stationarity of periodic spindle rhythms to detect transitions between multiple activities. The frequency domain method, based on normalized spectrum and bispectrum, describes frequency interactions associated with nonlinearities occurring in the observed EEG.

Adult↗

PubMed2006

Stepwise coupled mode scattering of ambient noise by a cylindrically symmetric seamount.

The question of how underwater ambient noise, at low frequencies, interacts with seamounts is addressed. The vertical directivity of the ambient noise, with and without the seamount interaction, is of particular interest. The problem of ambient noise scattering by seamounts motivates the development of a numerical modeling procedure, based on stepwise coupled modes. The procedure is designed to analyze scattering from a cylindrically symmetric seamount. The stepwise coupled mode procedure is extended to more general boundary conditions and brought up to date in the process. An example, using the geometry of the Dickins seamount, suggests that the seamount removes energy from the steeply traveling ambient noise, for this case. The energy is not converted into angles near the horizontal; the energy is lost through bottom interaction and attenuation.

Journal Article↗

PubMed1992

A peer-mediated social network intervention to enhance the social integration of persons with moderate and severe disabilities.

Increasingly, parents, teachers, and students with disabilities are advocating for interventions that go beyond skill training to provide support for participation in integrated environments and support for friendships. The present research demonstrated a social network intervention for youths with moderate and severe disabilities. Two groups of nondisabled peers were recruited to participate in weekly discussions with an adult integration facilitator to increase opportunities for social interaction for 2 students (1 with autism and 1 who was moderately mentally retarded). The groups met to discuss social interactions that had occurred with the students with disabilities and to talk about strategies to promote greater inclusion of the students into ongoing social interaction. The nondisabled students participated in the design and implementation of social skills interventions during transition times and lunch. The nondisabled students used self-monitoring data sheets to record the quantity and quality of interactions. The frequency of interaction, number of opportunities for interaction, and appropriateness of social interactions were analyzed with a multiple baseline design. Results indicated that the social network intervention was successful in increasing the quantity and quality of interactions and that the network strategy promoted the development of friendships. The results are discussed in terms of the need for additional research showing the relationships between increases in social competence, peer-mediated intervention, and the development and support of friendship.

Adolescent↗

PubMed2004

Effect of organic matter addition to the pen surface and pen cleaning frequency on nitrogen mass balance in open feedlots.

Three finishing trials were conducted to determine the effects of dietary manipulation and management on N losses from open feedlots. In each experiment, 96 steers were assigned randomly to 12 nutrient balance pens. In Trial 1, calves were fed for 180 d during the winter/spring months; in Trial 2, yearlings were fed for 132 d in the summer. In Trials 1 and 2, N losses from pens were compared directly by adding OM to the pen surface or indirectly by feeding digestible ingredients designed to increase OM excretion. The dietary treatment (BRAN) included 30% corn bran (DM basis) replacing dry-rolled corn. Pens where OM was directly added received sawdust applications (SAWDUST) at a rate to match OM excretion from the BRAN diet. These two treatments were compared with a conventional, 75% dry-rolled corn diet (CON). Because CON and SAWDUST diets were identical, performance for both treatments was similar during Trials 1 and 2. The BRAN diet decreased (P < 0.10) gain efficiency during Trials 1 and 2 by 9.5% relative to CON. Fecal N excretion was greater (P < 0.01) for calves and yearlings when BRAN was fed compared with CON. Adding OM to the pen surface increased (P < 0.01) the amount of N in manure removed from pens and reduced (P < 0.10) N losses in Trial 1. Nitrogen losses were not significantly different among treatments in Trial 2. In Trial 3, calves were fed for 166 d during the winter/spring months. A 2 x 2 factorial design was used to evaluate pen cleaning frequency and diets similar to CON and BRAN. Pens were either cleaned monthly or once at the end of the feeding period. Daily DMI was greater (P = 0.01) and ADG was lower (P < 0.01) when cattle were fed BRAN compared with CON. Responses from all three trials indicate a negative effect of BRAN on gain efficiency. Dietary treatment and cleaning frequency interacted for N balance in the feedlot. Nitrogen losses decreased and manure N increased (P < 0.10) for cattle fed BRAN compared with CON when pens were cleaned monthly. Feeding BRAN did not affect total manure N, but resulted in higher N losses when pens were cleaned only once. For all trials, BRAN increased the amount of N remaining in composted manure. Adding OM to pen surfaces and/or cleaning pens more frequently may decrease N losses from open feedlot pens and from compost, although responses seem influenced by ambient temperature or season.

Animal Feed↗

PubMed1986

Prevention of duodenal ulcer recurrence.

Recurrent duodenal ulcers, treated with cimetidine, 400 mg, or ranitidine, 150 mg, once nightly, or with sucralfate, 1 g twice daily, can be prevented in approximately 75% of patients for up to 1 year. Because these drugs are generally of equal efficacy, the choice is based on the patient's previous drug experience and tolerance, potential side effects, risk of drug interaction, frequency of administration, and cost. These medications do not alter the natural history of duodenal ulcer disease, and therapy may need to continue for longer than 1 year if there are no long-term side effects. Extra efforts should be made to help cigarette smokers discontinue smoking. Patients who have recurrent duodenal ulcers during maintenance therapy can be retreated with full-dose therapy. If optimal drug therapy is unsuccessful in preventing frequent recurrences or complications, surgical treatment is indicated.

Anti-Ulcer Agents↗

PubMedDate not supplied

Interactive videodisc instruction with undergraduate nursing students using cooperative learning strategies.

This study was conducted to explore the use of interactive videodisc instruction (IVDI) with cooperative learning strategies. Baccalaureate students in their junior year were assigned to one of three types of groups based on prenursing grade point average: homogeneous average achievement, homogeneous high achievement, and heterogeneous mixed achievement students. Groups of three to five students viewed a lesson related to auscultation of heart sounds using IVDI and were videotaped throughout the lesson. There were no significant differences among the groups in their interaction frequencies, cooperativeness, or achievement on the group posttest completed immediately after viewing the lesson. Homogeneous high achievement students scored significantly higher than the other two groups on the individual posttests given 2 weeks after viewing the lesson. However, all three groups had very low scores. Several themes emerged related to management of the lesson. A majority of the students without previous IVDI experience had difficulty accessing and proceeding through the lesson: fill-in-the-blank questions posed by the lesson often were frustrating to the students, students in groups had difficulty reading the touch screen monitor, a large number of students attempted to locate the cardiac valves on themselves or other group members, and male students tended to distance themselves from each other. In this study, students needed more orientation to the computer equipment and to cooperative learning strategies. When using IVDI with inexperienced students, faculty should be certain that technical assistance is available throughout the lesson.

Achievement↗

PubMed1998

Family interaction and migration decision making.

Using data from the Residential Preference and Migration Survey, a panel study of Pennsylvania households on migration intention and behavior, the authors examine some aspects of the decision to migrate. "We first examine the impact of the presence or absence of household interaction on the desire to move, migration expectations, and actual migration behavior. We hypothesize that the presence of household interaction is associated with migration behavior, while the absence of household interaction on migration-related issues is a predictor of staying in the present residence. Second, we test an expanded residential satisfaction migration decision model.... The expanded model permits us to test the thesis that household interaction frequency and consensus/conflict are moderating factors in explaining and predicting the outcome of migration decision making."

Americas↗

PubMedDate not supplied

[The problems of evaluating the automatized and exploratory intellectual actions of man].

On the basis of psychological testing two groups of subjects have been formed: "automatizators" and "searchers". The incompatibility in the individual structure of the ability to automatized and searching actions, according to the data, are connected with the presence of the complex of alternative signs of cognitive styles. The neurophysiological organization of searching and automatized intellectual actions was studied by a method of computer toposcopy of the synchronous electrical processes. It has been shown that there are spatial-frequency interactions of electrical processes of the cerebral cortex, characteristic for each of the two above mentioned individuals groups, which are probably based on the functioning of neuronal networks with different lability levels.

Adult↗

PubMedDate not supplied

[Action of drugs in relation to the administration route].

The factors capable of modifying the activity of a given drug may be divided into two categories: those related to the patient (age, sex, weight, state of health, genetic factors, etc.) and those related to the drug (pharmaceutical formulation, dose, dose frequency, interaction with other drugs taken more or less simultaneously and administration mode). One example of a drug whose action varies according to the mode of administration adopted is offered by the estrogens which may be given orally (estradiol valerianate, estriol, conjugated estrogens, etc.) or parenterally (estradiol valerianate intramuscularly; conjugated estrogens and estriol vaginally, estradiol as a skin gel, by subcutaneous implant or transdermally). Blood concentrations of estradiol and estrogen after the same dose vary considerably according to the administration mode adopted so that doses may have to be adjusted in order to achieve the same levels of the circulating hormone. Having no first pass effect on the liver, parenteral administrations have less influence than oral ones on the synthesis of certain proteins by the liver (increased SHBG, CBG, TBG, transferrin, ceruloplasmin, angiotensinogen, clotting factors VII, IX, X and X complex; decreased antithrombin III and anti Xa) and on lipid metabolism (increased biliary cholesterol, triglycerides and HDL, especially HDL2; reduced LDL). In particular, it has been found that estradiol (differently from other estrogens) when administered transdermically is able to relieve menopausal symptoms at doses which do not influence the liver synthesis of proteins.

Administration, Cutaneous↗

PubMed1982

Combined effect of beating rate and hydrostatic pressure on excitation in cardiac muscle.

Canine cardiac Purkinje fibers stimulated at frequencies from 1-4 Hz were exposed to hydrostatic pressures of 1 and 150 ATA. Both increases in stimulation frequency and pressure slowed conduction and decreased maximum upstroke velocity of the action potential. Depression of these variables was greatest when rapid rate and elevated pressure were combined. Membrane potential decreased at 150 ATA at all frequencies. Post-overdrive hyperpolarization was reduced 45% at 150 ATA. Action potential duration increased at 150 ATA at all frequencies. Elevated pressure had no effect on the interval dependence of repolarization time to -60 mV but had a slight effect on time to full repolarization. Pressure effect on resting potential was reduced in elevated extracellular potassium. Arrhythmias developed in more than 50% of the tissues at 150 ATA and a frequency of 4 Hz. The results are discussed with respect to ionic mechanisms underlying action potential propagation, to electrogenic pump activity, and to the arrhythmogenic nature of pressure-frequency interactions.

Action Potentials↗

PubMed1978

In-111 transferrin labeling studied by perturbed angular correlations.

The technique of perturbed angular correlations (P.A.C.) was used to study transferrin labeled with radioactive indium. Three forms of the labeled system were studied: a) the In-111 was bound to transferrin with no iron present at either of the binding sites; b) the In-111 probe was used to label transferrin that was 33% saturated with iron; and c) the label was attached to saturated Fe-transferrin. The measured perturbation factors, G22(t), indicate that the three binding states are clearly differentiated. Cases (a) and (b) exhibit characteristic features of time-independent quadrupole interactions and the average quadrupole interaction frequencies, omegaq, were determined in these cases.

Binding Sites↗

PubMedDate not supplied

Two-frequency analysis of interactions elicited by Vernier stimuli.

In five subjects, we measured visual evoked potentials (VEPs) elicited by Vernier targets in which the contrast of the two components of the stimuli were modulated by sinusoids at distinct frequencies fl and f2. This approach allows for the extraction of VEP signatures of spatial interactions, namely, responses at intermodulation frequencies n1f1 + n2f2, without the need to introduce motion into the stimulus. The most prominent interactions were at the sum frequency f1 + f2, and, for frequency pairs that were sufficiently separated, the difference frequency f1- f2. These responses had a systematic dependence on the temporal parameters of the stimulus, corresponding to an effective latency of 145 to 165 ms. Fourth-order interactions were also detected, particularly at the frequencies 2f1 +/- 2f2. These VEP signatures of interaction were similar to interactions seen for colinear line segments separated by a gap. Thus, for Vernier stimuli devoid of motion, VEP signatures of interaction are readily detected but are not specific to hyperacuity displacements. The distribution of interactions across harmonic orders is consistent with local rectification preceding the spatial interactions. Their effective latencies and dependence on spatial parameters are consistent with interactions within V1 receptive fields or mediated by horizontal connections between cells with a similar orientation tuning within V1.

Adult↗

PubMedDate not supplied

The interactions of intensity, frequency and duration of exercise training in altering cardiorespiratory fitness.

This review has grouped many studies on different populations with different protocols to show the interactive effects of intensity, frequency and duration of training as well as the effects of initial fitness levels and programme length on cardiorespiratory fitness as reflected by aerobic power (VO2max). Within each level of exercise duration, frequency, programme length or initial fitness level, the greatest improvements in aerobic power occur when the greatest challenge to aerobic power occurs i.e., when intensity is from 90 to 100% of VO2max. The pattern of improvement where different intensities are compared with different durations suggests that when exercise exceeds 35 minutes, a lower intensity of training results in the same effect as those achieved at higher intensities for shorter durations. Frequencies of as low as 2 per week can result in improvements in less fit subjects but when aerobic power exceeds 50 ml/kg/min, exercise frequency of at least 3 times per week is required. As the levels of initial fitness improve, the changes in aerobic power decreases regardless of the intensity, frequency or duration of exercise. Although these pooled data suggest that maximal gains in aerobic power are elicited with intensities between 90 to 100% VO2max, 4 times per week with exercise durations of 35 to 45 minutes, it is important to note that lower intensities still produce effective changes and reduce the risks of injury in non-athletic groups.

Aerobiosis↗

PubMed2006

The population genetics of sporophytic self-incompatibility in Senecio squalidus L. (Asteraceae): the number, frequency, and dominance interactions of S alleles across its British range.

Sporophytic self-incompatibility (SSI) was studied in 11 British Senecio squalidus populations to quantify mating system variation and determine how its recent colonization of the United Kingdom has influenced its mating behavior. S allele number, frequency, and dominance interactions in populations were assessed using full diallels of controlled pollinations. A mean of 5.1 S alleles per population was observed, and no population contained more than six S alleles. Numbers of S alleles within populations of S. squalidus declined with increasing distance from the center of its introduction (Oxford). Cross-classification of S alleles allowed an estimate of approximately seven and no more than 11 S alleles for the entire British S. squalidus population. The low number of S alleles observed in British S. squalidus compared to other SI species is consistent with the population bottleneck associated with S. squalidus' introduction to the Oxford Botanic Garden and subsequent colonization of Britain. Extensive S allele dominance interactions were observed to be a feature of the S. squalidus SSI system and may represent an adaptive response to improve limited mate availability imposed by the presence of so few S alleles. Multilocus allozyme genotypes were also identified for individuals in all populations and geographic patterns of S locus and allozyme loci variation investigated. Less interpopulation structure was observed for the S locus than for allozyme diversity--a finding indicative of the effects of negative frequency-dependent selection at the S locus maintaining equal S phenotypes within populations and enhancing effective migration between populations.

Alleles↗

PubMed2006

The interaction of word frequency and word class: a test of the GO model's account of the missing-letter effect.

When asked to detect target letters while reading a text, participants miss more letters in frequent function words than in less frequent content words. In this phenomenon, known as the missing-letter effect, two factors covary: word frequency and word class. According to the GO model, there should be an interaction between word class and word frequency with more omissions for function than for content words only among high-frequency words. This pattern would be due to the fact that function words could only assume a structure-supporting role if they are identified rapidly, which is only possible for high-frequency words. These predictions were tested by assessing omission rate for frequent and rare function and content words. Results lend support to the GO model with more omissions for frequent than for rare words, and more omissions for the function than for the content word among high-frequency words, but not among low-frequency words. These results were observed both in English (Experiment 1) and in French (Experiment 2).

Female↗

PubMed1997

Interactions of spatial frequency and unequal monocular contrasts in stereopsis.

Increasing the contrast of just one eye's image degrades stereothresholds; this phenomenon is referred to as the stereo contrast paradox. In experiment one, this paradox was found to be absent in dynamic random-element stereograms; thresholds were simply limited by the lower of the two eyes' contrasts. In experiment two, in which narrowband Gabor targets were used, the paradox was found to be strongest at relatively low spatial frequencies (1 cycle deg-1). As spatial frequency was increased, the paradox gradually disappeared. At relatively high spatial frequencies (5 cycles deg-1), thresholds were generally limited by the lower of the two eyes' contrasts, as was found for the dynamic noise targets. These results demonstrate the interactions of spatial frequency and contrast in binocular image combination and yield clues as to the different roles which high and low spatial frequencies may play in stereopsis.

Contrast Sensitivity↗

PubMed1980

Competitive intransitivity and size-frequency distributions of interacting populations.

The competitive ranking of three marine sessile organisms was determined from overgrowth observations and found to be intrasitive. Overgrowth results were dependent upon relative vertical relief which, in turn, was related to colony area. Discriminant function analysis demonstrates that competitive rankings can be largely predicted on the basis of knowledge of the size-frequency distribution of interacting populations. Because size increases with age for these species, size-dependent competition implies age-dependent competition. The role of age structure in determining the results of inter-specific interactions has been curiously neglected, particularly as it relates to competitive ability, yet the age dependence of competitive ability suggests (i) the occurrence of intransitivity in purely exploitative systems, (ii) a mechanism for frequency-dependent behavior, (iii) the production of limit cycles, and (iv) the possibility of size refugia.

Journal Article↗

PubMedDate not supplied

Natural scene statistics and nonlinear neural interactions between frequency-selective mechanisms.

Linear filtering is a basic concept in neural models of early sensory information processing. In particular the visual system has been described to perform a wavelet-like multi-channel decomposition by a set of independent spatial-frequency selective filter mechanisms. Here we suggest that this principle of linear filtering deserves a critical re-evaluation. We propose that an optimal adaptation to natural scene statistics would require AND-like nonlinear interactions between the frequency-selective filter channels. We describe how this hypothesis can be tested by predicted violations of the principle of linearity that should be observable if cortical neurons would actually implement the proposed nonlinearities. We further explain why these effects might have been easily overlooked in earlier tests of the linearity of neurons in primary visual cortex.

Neurons↗