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Results for “interaction frequencies”

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PubMedDate not supplied

Interactions between hydrophobic and hydrophilic silicon surfaces using a tapered probe in near-field scanning optical microscopy.

We examined the tip-sample interaction of a Si(111) surface processed with HF solution. The interaction length of the probe with its hydrophobic surface is approximately 30, and the frequency responses show an interaction force of elastic type. By contrast, the damping curve on a hydrophilic surface, Si with thin oxide, operates on a longer length of 100. Here, the frequency responses indicate an interaction force of the viscous type.

Journal Article↗

PubMed1971

Kinetic theory model for ion movement through biological membranes. II. Interionic selectivity.

The equation presented in the previous paper for steady-state membrane ionic current as a function of externally applied electric field strength is numerically analyzed to determine the influence of ionic and membrane molecule parameters on current densities. The model displays selectivity between different ions. A selectivity coefficient S(i), defined as the ratio of current carried by an ionic species i at a given field strength to the current carried by a reference species at the same field strength, has the following properties: (a) S(i) is a function of electric field strength except for ion-membrane molecule interactions yielding velocity independent collision frequencies; (b) for ion-membrane molecule interactions characterized by a collision frequency that is a decreasing (increasing) function of increasing ionic velocity, ions whose S(i) > 1 (<1) at zero field strength will show maxima (minima) (minima[maxima]) in their S(i) vs. electric field strength curves.

Ammonia↗

PubMed2003

Personal strivings and marijuana use initiation, frequency, and problems.

This study examined relations between perceived conflict/utility of marijuana use in achieving valued personal goals and marijuana use initiation, marijuana use frequency, and marijuana-related problems. Personal strivings are higher order goals that may influence marijuana use to the extent that they are congruent or incongruent with use. Participants were 592 young adults who generated lists of personal strivings independent of the substance use assessment. They then evaluated their 10 most important strivings with regard to the perceived conflict/utility of several levels of marijuana use in achieving their most important strivings. Less marijuana use-striving conflict was positively associated with use initiation and frequency. A significant gender interaction emerged in the prediction of use frequency; marijuana use-striving conflict was more strongly associated with use frequency for men than women. The relationship between use-striving conflict and marijuana-related problems was mediated fully by use frequency.

Adolescent↗

PubMed1999

Measured and modeled properties of mammalian skeletal muscle. II. The effects of stimulus frequency on force-length and force-velocity relationships.

Interactions between physiological stimulus frequencies, fascicle lengths and velocities were analyzed in feline caudofemoralis (CF), a hindlimb skeletal muscle composed exclusively of fast-twitch fibers. Split ventral roots were stimulated asynchronously to produce smooth contractions at sub-tetanic stimulus frequencies. As described previously, the peak of the sub-tetanic force-length relationship was found to shift to longer lengths with decreases in stimulus frequency, indicating a length dependence for activation that is independent of filament overlap. The sub-tetanic force-velocity (FV) relationship was affected strongly both by stimulus frequency and by length; decreases in either decreased the slope of the FV relationship around isometric. The shapes of the force transients following stretch or shortening revealed that these effects were not due to a change in the instantaneous FV relationship; the relative shape of the force transients following stretch or shortening was independent of stimulus frequency and hardly affected by length. The effects of stimulus frequency and length on the sub-tetanic FV relationship instead appear to be caused by a time delay in the length-dependent changes of activation. In contrast to feline soleus muscle, which is composed exclusively of slow-twitch fibers, CF did not yield at sub-tetanic stimulus frequencies for the range of stretch velocities tested (up to 2 L0/s). The data presented here were used to build a model of muscle that accounted well for all of the effects described. We extended our model to account for slow twitch muscle by comparing our fast-twitch model with previously published data and then changing the necessary parameters to fit the data. Our slow-twitch model accounts well for all previous findings including that of yielding.

Action Potentials↗

PubMed1991

Inability to predict the adult sexual performance of bulls by prepuberal sexual behaviors.

The objective of this investigation was to determine the extent to which the sexual performance of adult bulls (18 to 24 mo of age) can be predicted by prepuberal sexual behaviors. Tests were administered to 121 polled Hereford bulls to determine whether adult sexual performance (especially serving capacity or ejaculation rate) was related to 1) whether or not the subjects mounted estrous females at 6 mo of age, 2) the age at which the bulls attained their first ejaculation, 3) the frequency of sexual behaviors exhibited in heterosexual interactions and 4) the frequency of male-male mounting exhibited in all-male groups. None of the above measures reliably predicted adult serving capacity. Prepuberal interest in mounting other males and estrous females and the age at which ejaculatory competence was attained bore little relationship to serving capacity at 18 to 24 mo. Individual differences in rate of ejaculation were consistent from one age to another only after the bulls had reached 18 mo. We concluded that the sexual behaviors of prepuberal beef bulls were of limited usefulness in predicting adult sexual performance.

Animals↗

PubMed2000

Lack of preference for low-predation-risk habitats in larval damselflies explained by costs of intraspecific interactions.

Many studies indicate prey organisms select microhabitats with high structural complexity as a way of reducing risk of predation. We used laboratory experiments to show that damselfly larvae, Ischnura verticalis, suffer higher predation rates from pumpkinseed sunfish in low-density vegetation. However, larvae do not preferentially occupy microhabitats with high vegetation density in either the presence or absence of sunfish; when given a choice, the number of larvae per stem of vegetation was equal across all densities of vegetation. That larvae do not congregate in dense vegetation may reflect costs of aggressive interactions. Results from laboratory experiments indicated larval interactions increase conspicuous behaviours (most notably swimming) and consequently increase fish predation. A subsequent experiment indicated that frequency of larval interactions increases with increased vegetation density when number of larvae/stem is constant. Thus, larval microhabitat selection may reflect a trade-off between reduced risk of predation in areas of high vegetation density, caused by reduced fish foraging ability, and increased aggressive larval interactions, due to decreased proximity of larvae. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1982

Influence of male aggression on mating of gorillas in the laboratory.

The frequency of sexual interactions between oppositely-sexed pairs of gorillas tested in the laboratory was directly related to the frequency of male aggression directed toward the female. The data suggest that male aggression stimulated female presenting and copulation, and accounted for mating temporally dissociated from the periovulatory period. Among the great apes tested in the laboratory, the male primarily accounts for mating that is unlikely to contribute to reproduction.

Aggression↗

PubMed1994

A national survey of public health officers' interactions with the media.

OBJECTIVES: To assess the perceptions, practices, and needs of state and local health officers with respect to professional interactions with the media. DESIGN: A survey of 759 public health officers (56 state and 703 local) on jurisdiction demographics, frequency of media interactions, agency process for media contacts, provision and need for media training, and character of media relations. PARTICIPANTS: Fifty-two state health officers and 568 US local health officers responded, for a survey response rate of 82%. RESULTS: Media reporting was perceived as accurate 52% to 73% of the time, although reporters were seen as needing improved technical and scientific knowledge. Media were used frequently as a component of health education. State health jurisdictions were more likely than local jurisdictions to have a media protocol and designated media contact, to internally review media releases, to interact regularly with media, and to provide staff training on media relations. Media interaction time comprised print media (63%), television (19%), and ratio (17%). One third of the health officers found media relations adversarial, but most held a positive overall view of the media. Favorable evaluation of the media was associated with high frequency of media contact, high perceived accuracy of reporting, and presence of an institutional media protocol. CONCLUSIONS: While health officers evaluated media favorably, problem areas were identified where mutual education could improve the accuracy and value of media reporting on health issues. Training capacity for both professions should be developed to increase the effectiveness of public health in media relations.

Communication↗

PubMed1975

Binaural beats at high frequencies.

Binaural beats have long been believed to be audible only at low frequencies, but an interaction reminiscent of a binaural beat can sometimes be heard when different two-tone complexes of high frequency are presented to the two ears. The primary requirement is that the frequency separation in the complex at one ear be slightly different from that in the other--that is, that there be a small interaural difference in the envelope periodicities. This finding is in accord with other recent demonstrations that the auditory system is not deaf to interaural time differences at high frequencies.

Auditory Pathways↗

PubMed2002

Age of acquisition and word frequency: determinants of object-naming speed and accuracy.

The combined contributions of word age of acquisition (AoA) and word frequency (rated and objective) to word retrieval speed and accuracy were investigated, using a picture-naming paradigm. Results from two fully factorial studies revealed that both AoA and word frequency reliably facilitate the speed and accuracy of word retrieval. Furthermore, word frequency and AoA interacted across delay (0, 750, 1,500, and 2,250 msec) in Experiment 2. This resulted in word frequency's playing a stronger role for late-acquired words across delays. It is concluded that both AoA and word frequency play a fundamental role in lexical retrieval. The results are also consistent with the view that both factors affect the same processing stages.

Adolescent↗

PubMed1988

Social interaction and depression in elderly individuals.

Forty-two elderly individuals received partial or complete testing on: (a) the Zung Self-Rating Depression Scale; (b) frequency of social interaction (quantity of social interaction); and (c) round-robin reports of disclosures among peers, that yielded whether the persons had reciprocally intimate relationships (quality of social interaction). It was found that depression was: (a) negatively correlated with the measure of the quantity of social interaction entailing frequent conversations; and (b) contrary to expectation, positively correlated with having reciprocally intimate relationships. Also, the individuals' intimacy of disclosure to peers was not correlated with the intimacy of disclosure received from them; indicating a lack of reciprocity of self-disclosure. The findings were interpreted as showing that depression in elderly individuals is negatively related to having peers to "talk to" frequently, but positively related to having reciprocal exchanges of negative communications.

Aged↗

PubMedDate not supplied

[Posttetanic changes in the background gamma oscillations in interhemispheric interactions].

The influence of high-frequency microstimulation (HFMS) of one of the hemispheres on the parameters of spontaneous gamma-oscillations in the neural network containing callosal cells of the motor cortex of both hemispheres. There were three modes in the background oscillation periods distribution, which corresponded to the frequencies 40-60, 70-100, and 100-200 Hz. These oscillation frequencies were also revealed after the HFMS in neural interactions of the cells, which were active before the HFMS; the frequency 40-60 Hz, which dominated before the HFMS, became even more pronounced. The same three groups of oscillation frequencies were found in the activity of cells which became active after the HFMS. The expression of oscillations, the number of oscillatory interactions, as well as the number of neuronal pairs with additional synchronization decreased after the HFMS, which suggests a decrease in synchronization. Taking into account the results of simulation experiments that the frequency of gamma-oscillations is determined by the strength of inhibitory and excitatory input, we suggest that the long-term posttetanic modifications in the efficacy of synaptic inputs of the neurons of both hemispheres underlie the observed posttetanic changes.

Action Potentials↗

PubMed1986

MAV-2-O replicates at a reduced rate in cells from the osteopetrosis resistant G-B1 chicken.

The replication of the avian osteopetrosis virus MAV-2-O was compared in chick embryo fibroblasts from two strains of chicken. These were G-B1 which is relatively resistant to MAV-2-O and CB which is susceptible. The production of MAV-2-O was delayed in G-B1 cells (compared with CB cells). The same result was observed after infection with Rous sarcoma viruses of subgroups B, C, and D. In addition, the transforming viruses induced foci on G-B1 fibroblasts 24 to 48 hours later than on CB fibroblasts. In G-B1 cells there was also a delayed kinetics of intracellular viral RNA production. Integrated and linear unintegrated MAV-2-O DNA species were also present in lower amounts in G-B1 than in CB fibroblasts at 3 days postinfection. In vivo studies confirmed the in vitro situation. There was a marked difference in the amount of virus present in the osteoid bone matrix and the osteocytic lacunae of osteopetrotic bones from susceptible and G-B1 chickens. In contrast to the bone lesions from susceptible animals, budding virus particles were not detectable in lesions from G-B1 chickens. There was no difference in the amount of virus in osteopetrotic and non-osteopetrotic bone of susceptible chickens suggesting that virus replication alone is not sufficient for induction of osteopetrosis and that an additional specific virus-cell interaction is required. The relative resistance of strain G-B1 may therefore, be a consequence of a reduced frequency of this interaction. Its basis may be the lower amount of integrated, as well as unintegrated, viral DNA.

Animals↗

PubMed1992

Word frequency and multiple repetition as determinants of the modulation of event-related potentials in a semantic classification task.

We recorded event-related potentials while subjects performed a category membership decision task. The stimuli were words of high and low frequency of occurrence in written English, and each was presented four times. The experiment was intended to explore the interaction of word frequency and multiple repetition on the event-related potential, and thence to investigate the possible loci in time of the effects of these variables. First presentations of low and high frequency words evoked event-related potentials which differed in the presence, in the low word frequency waveforms, of a right-hemisphere dominant negativity peaking at 400 ms. This negativity was very similar to the N400 which may be sensitive to the semantic relations among words in a sequence. Initial repetition diminished this midlatency difference, but gave rise to both earlier and later frequency-related differences. Subsequent multiple repetition abolished the early frequency-related repetition effect, but did not affect amplitudes in the region of N400, nor did it abolish a late positivity, present only for repeated low frequency words.

Adult↗

PubMed1980

Pattern-sensitive epilepsy. I: A demonstration of a spatial frequency selective epileptic response to gratings.

Rare individuals suffer epileptic seizures when they view certain images, particularly stripes. Contrast-threshold functions (the ability to see faint stripes of various widths) were determined for two pattern-sensitive brothers, and the epileptogenicity of various patterns was assessed for one of them. Sine wave grating contrast-detection thresholds for the two subjects were essentially normal, with lowest thresholds at approximately 2 cycles/degree (c/deg). Epileptiform discharges occurred maximally at 5 c/deg with a 1-octave 50% bandwidth. Pattern epileptogenicity was increased by the addition of a third harmonic sine wave grating to its fundamental, but was unaffected by the phase relation of the two gratings. The frequency selectivity of epileptic responsiveness was quantitatively similar to a "spatial frequency channel." Inhibitory interaction were not present. The findings suggest relations between the phenomena of pattern-sensitive epilepsy and hypothesized spatial frequency channels which merit further exploration.

Adolescent↗

PubMed2003

Effects of frequency and similarity neighborhoods on pharmacists' visual perception of drug names.

To minimize drug name confusion errors, regulators, drug companies, and clinicians need tools that help them predict which names are most likely to be involved in confusions. Two experiments, carried out in the United States, examined the effects of stimulus frequency (i.e., how frequently a target name is prescribed), neighborhood frequency (i.e., how frequently prescribed are the "neighbors" of the target name), and neighborhood density (how many names are within a fixed distance of the target name) on the probability of pharmacists making an error in a visual perceptual identification task. In both experiments, the task was to correctly identify a series of blurry drug names after a 3s presentation on a computer monitor. In the first experiment, 45 pharmacists viewed 160 typewritten names, incorrectly identifying 60.6% of them. Random effects regression revealed a significant beneficial effect of stimulus frequency and a detrimental effect of neighborhood density. Significant two-way interactions were observed between stimulus frequency and neighborhood density and neighborhood frequency and neighborhood density. In the second experiment, 37 pharmacists viewed 156 handwritten drug names, incorrectly identifying 45.7%. Random effects regression revealed significant main effects of stimulus frequency and neighborhood density. These were contained within a significant three-way interaction: The interaction between stimulus frequency and neighborhood density was present at high but not low neighborhood frequency. Objectively measurable frequency and neighborhood characteristics have predictable effects on errors in pharmacists' visual perception. Organizations that coin and evaluate drug names, as well as hospitals, pharmacies, and health systems, should consider these characteristics when assessing visually confusing names.

Decision Making↗

PubMed1998

Lexical representation of gender: a quasiregular domain.

The relationship between gender and word ending in French is a quasiregular one (e.g., most words ending in -ette are feminine, but not all). As such, the gender of low-frequency irregular forms (e.g., squelette, which is masculine) should take longer to classify than low-frequency regular forms according to neural network models. A regularity effect was found in Experiment 1, but it did not interact with word frequency. It was further revealed that there was difficulty in making gender decisions (Experiment 2) and gender verification responses (Experiment 3) to words whose endings were highly informative of gender, but whose associated article was not. These words were place names beginning with a vowel, like Australie, which do not take an indefinite article and whose definite article is ambiguous (1'). How a neural network might handle these results is discussed, and an alternative account is considered whereby there are two potential sources of gender information, lexical and nonlexical, with the latter being used to confirm the former.

Female↗

PubMed2003

Efficient frequency doubling by a phase-compensated crystal in a semimonolithic cavity.

In multiple-pass nonlinear frequency conversion devices, interacting waves may accumulate different phases, owing to dispersive elements in the system. Phase compensation is therefore necessary for efficient frequency conversion. We experimentally demonstrate phase compensation in a compact semimonolithic frequency-doubling cavity by using a periodically poled KTP crystal. The conversion efficiency of the crystal was found to decrease at high pump powers, owing to power-dependent thermal lensing. This experimental observation was supported by a theoretical calculation of the conversion efficiency in a cavity, considering the mismatch between the mode's thermally loaded and unloaded cavities. A design procedure was also presented to compensate for the thermal lensing effect. The highest conversion efficiency of 56.5%, corresponding to a second-harmonic power of 117.5 mW at 532 nm, was achieved with a cw Nd:YAG pump power of 208 mW.

Journal Article↗