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PubMed1999

Center frequency modulation detection for harmonic complexes resembling vowel formants and its interference by off-frequency maskers.

Vowels are characterized by peaks in their spectral envelopes: the formants. To gain insight into the perception of speech as well as into the basic abilities of the ear, sensitivity to modulations in the positions of these formants is investigated. Frequency modulation detection thresholds (FMTs) were measured for the center frequency of formantlike harmonic complexes in the absence and in the presence of simultaneous off-frequency formants (maskers). Both the signals and the maskers were harmonic complexes which were band-pass filtered with a triangular spectral envelope, on a log-log scale, into either a LOW (near 500 Hz), a MID (near 1500 Hz), or a HIGH region (near 3000 Hz). They had a duration of 250 ms, and either an 80- or a 240-Hz fundamental. The modulation rate was 5 Hz for the signals and 10 Hz for the maskers. A pink noise background was presented continuously. In a first experiment no maskers were used. The measured FMTs were roughly two times larger than previously reported just-noticeable differences for formant frequency. In a second experiment, no significant differences were found between the FMTs in the absence of maskers and those in the presence of stationary (i.e., nonfrequency modulated) maskers. However, under many conditions the FMTs were increased by the presence of simultaneous modulated maskers. These results indicate that frequency modulation detection interference (FMDI) can exist for formantlike complex tones. The FMDI data could be divided into two groups. For stimuli characterized by a steep (200-dB/oct) slope, it was found that the size of the FMDI depended on which cues were used for detecting the signal and masker modulations. For stimuli with shallow (50-dB/oct) slopes, the FMDI was reduced when the signal and the masker had widely differing fundamentals, implying that the fundamental information is extracted before the interference occurs.

Auditory Threshold↗

PubMed1999

The frequency of conjugative transposition of Tn916 is not determined by the frequency of excision.

Excision and formation of a covalently closed circular transposon molecule are required for conjugative transposition of Tn916 but are not the only factors that limit the frequency of conjugative transposition from one host to another. We found that in gram-positive bacteria, an increase in the frequency of excision and circularization of Tn916 caused by expression of integrase (Int) and excisionase (Xis) from a xylose-inducible promoter does not lead to an increase in the frequency of conjugative transposition. We also found that the concentration of Int and Xis in the recipient cell does not limit the frequency of conjugative transposition and that increased excision does not result in increased expression of transfer functions required to mobilize a plasmid containing the Tn916 origin of transfer. We conclude that in gram-positive hosts in which the Tn916 functions Int and Xis are overexpressed, the frequency of conjugative transposition is limited by the availability of transfer functions.

Bacillus subtilis↗

PubMed1987

Frequency code: orofacial correlates of fundamental frequency.

In the human voice, lip retraction as in smiling can be associated with high fundamental (Fo) and formant frequencies. The aim of this study was to investigate under naturalistic conditions the cross-species generality of the frequency code hypothesis and related orofacial correlates in Fo. Digital spectral, spectrographic, and cinegraphic measurements were made of spontaneous chimpanzee vocalizations and orofacial movements produced and recorded in the field. A significant decline in Fo was found in submissive-scream-to-aggressive-waahbark transitions as predicted by the frequency code. Teeth and lip opening distances during sounds were positively correlated with their duration, Fo, frequency rise and tempo. These positive correlates and a trivariate regression between orofacial opening and Fo give support to the coordination of these appeasing facial and vocal features proposed in the frequency code hypothesis.

Acoustics↗

PubMed1985

Spatial-frequency discrimination at low frequencies: evidence for position quantization by receptive fields.

In a recent study of spatial-frequency discrimination [J. Opt. Soc. Am. 72, 1367 (1982)], we reported evidence for the quantization of position in the human visual system with the fundamental unit of quantization being the photoreceptor spacing for spatial frequencies greater than 2 cycles per degree (c/deg). In this paper we extend our measurements to lower spatial frequencies, between 0.3 and 2, which we call the mid-spatial-frequency band, and find that this band of spatial frequencies shows similar evidence for spatial quantization. However, the spacing of the fundamental unit is about 0.056 deg or approximately seven or eight times the spacing of the foveal photoreceptor instead of about 0.008 deg or approximately equal to the spacing of foveal cones. We interpret this as evidence for a class of retinal receptive fields that we call spatial-sampling fields that perform a dual function of neural blurring and spatial sampling. We propose a scaled lattice model of spatial vision that allows apparently scale-free spatial processing while retaining the advantages of linear maps. The model generalizes the notion of hyperacuity to low-resolution tasks for which neural interpolation occurs not only on the photoreceptor sampling lattice to achieve hyperacuity but also on receptive-field sampling lattices to achieve lower resolutions.

Discrimination, Psychological↗

PubMed1988

Spatial-frequency tuning as a function of temporal frequency and stimulus motion.

Spatial-frequency tuning at two different spatial frequencies was determined by measuring the detectability of a signal grating that was made difficult to see by low- or high-pass visual noise. The signals were vertical sinusoidal gratings of different spatial frequencies. The detectability of the signal was measured in two-alternative forced-choice tasks with different temporal envelopes: (1) a slowly changing raised-cosine (Hanning) window, (2) a rectangularly gated 2-Hz counterphase flickering envelope, and (3) a rectangularly gated 10-Hz counterphase flickering envelope. Additional measurements were made using drifting stimuli with the signal and noise drifting in the same or in opposite directions. The temporal envelopes were chosen because they have different effects on the contrast-sensitivity function and it was desired to know how temporal factors affect the spatial-frequency tuning of the relatively narrowly tuned channels thought to underlie contrast sensitivity. The results show that, for counterphase flickering stimuli, spatial-frequency tuning does not depend on temporal envelopes applied identically to the signal and to the masking noise. A similar picture emerges at slow (2.7-deg/sec) but not at fast (10.9-deg/sec) drift rates.

Contrast Sensitivity↗

PubMed2003

2.1-microm lasers frequency stabilized against CO2 lines: comparison between fringe-side and frequency-modulation locking methods.

A comparison between the use of the fringe-side and the frequency-modulation methods to frequency stabilize diode-pumped Tm-Ho:YAG lasers against linear absorption lines of CO2 near 2.1 microm is reported. Frequency stability was evaluated by monitoring of the beat signal between two independently stabilized Tm-Ho:YAG systems. Frequency instability levels of approximately 20 and approximately 400 kHz for 1-s integration time were achieved by the frequency-modulation and fringe-side methods, respectively.

Journal Article↗

PubMed2005

Common-mode-free frequency comparison of lasers with relative frequency stability at the millihertz level.

We report on a frequency comparison of frequency-stabilized lasers located in remote laboratories resting on different foundations. By locating the lasers in this way correlated frequency excursions of the lasers are suppressed to a high degree. The beat signal between them shows a linewidth at the hertz level for averaging times of 1 s. The optical link is established by a 100 m single-mode optical fiber where the frequency noise induced by the fiber is reduced to the level of a few tens of millihertz. One laser is stabilized onto a Fabry-Perot resonator with a long-term precision of 25 mHz (fractional frequency instability, sigma(y) = 1.2 x 10(-16)), the highest lock fidelity obtained so far to our knowledge.

Journal Article↗

PubMed1985

Extra-high-frequency noise remotely masks and alters temporal integration at lower frequencies.

A quasi-free-field technique was used to assess the effects of extra-high-frequency-band masking on detection threshold of middle and high (1-7 kHz) frequencies. At an SPL of 60 dB, the 10- to 20-kHz masker produced a slight amount of masking. Increasing the masking level by another 5 dB produced a disproportionate increase of the detection thresholds. This increase was greatest in response to 4- and 5-kHz stimuli, and was detected with both constant and pulsed tones. Decreasing the bandwidth of the masker reduced the magnitude of the effect, but not the frequency-specific pattern of the remote masking. Extra-high-frequency masking also increased the amount of temporal integration at middle and high frequencies. The data are discussed in reference to peripheral and central neural changes associated with sensorineural hearing loss.

Adult↗

PubMed1999

The high frequency testing of vascular grafts and vascular stents: influence of sample dimensions on maximum allowable frequency.

There are over four dozen companies developing new products for the lucrative vascular graft and vascular stent markets. We have been studying the procedures used to pre-test vascular grafts, vascular stents, and mock arteries into which vascular stents are placed, so that appropriate high frequency durability/fatigue studies can be done in as short a time as possible, but also in a manner in which the data are highly reliable and dependable. In the past, we have evaluated the testing of the natural frequency response of the grafts, mock arteries, and stents in order to determine the frequencies that can be used for long-term life testing. In this paper, we present experiments that evaluate how product geometry affects product frequency response at various loading pressures. Results show that changing the dimensions of the device to be tested such that less fluid has to be injected (in the case of hydrodynamically driven experiments) results in the ability to test these products at a higher frequency.

Blood Vessel Prosthesis↗

PubMed1991

[Temperature control of the crossing-over frequency in Drosophila melanogaster. Effect of infra- and super-optimal shock temperatures in early ontogenesis on the recombination frequency].

Effect of temperature shock treatments (0 and 37 degrees C) in early ontogenesis on recombination frequency was studied in two strains of Drosophila X1 and X2. Recombination frequency under treatment with temperature of 0 degrees C and 37 degrees C (shock treatment), as well as at 14 degrees C and 29 degrees C nonshock treatment was found to be dependent on strain genotype, the chromosomal segments under consideration, developmental stage and the age of individuals analysed. Shock treatments usually increase recombination frequency, whereas nonshock treatments lead to unstable and variable recombination frequencies. A concept of ontogenic homeostasis of recombination has been introduced. It is assumed that the effect of temperature treatments on recombination frequency is indirect--i.e. physiologically mediated.

Animals↗

PubMed1983

Limiting dilution analysis of the frequency of human T cells and large granular lymphocytes proliferating in response to interleukin 2. I. The effect of lectin on the proliferative frequency and cytotoxic activity of cultured lymphoid cells.

Human peripheral blood LGL that mediated NK and small T cells were isolated in high purity (98% by morphology) by density sedimentation on discontinuous Percoll gradients. The proliferative frequency of these subpopulations in the presence of lectin-free conditioned media containing IL 2 was determined by limiting dilution analysis. LGL showed a 20-fold greater frequency of proliferative cell precursors than small T cells (1/200 and 1/4970, respectively). The NK-like nature of cells expanded from LGL preparations in IL 2 was confirmed by parallel testing of the cytotoxicity against K562. Whereas T cell microcultures showed no lytic activity against K562 (cytotoxic precursor frequency less than 1/10,000), LGL cultures showed frequencies of cytotoxic precursors (1/170) comparable to those of proliferative precursors. Neither responder cell type gave rise to detectable lytic activity against NK-insusceptible mouse lymphoma RL male 1 or alloblasts. LGL proliferation was only minimally affected by the presence of PHA at the onset of culture (rise to 1/74 with 2 micrograms/ml PHA). By contrast, small T cells showed a dose-dependent increase of proliferative frequency, to reach 1/11 with 2 micrograms/ml PHA, provided accessory cells in the form of PBMC, monocytes, or LGL but not T cells were present. The cytotoxic activity of LGL and small T cells expanded in IL 2 was confirmed in bulk cultures. LGL-CLC showed high lytic activity against NK-susceptible cell lines and a majority of freshly isolated allogeneic human tumor targets. T cell-CLC showed little activity against cell line targets (K562, Raji, L1210, RL male 1) but were lytic for some fresh tumor cells. These data establish optimal conditions for the growth of human LGL in IL 2-dependent culture and suggest that a major contributor to lysis of allogeneic human tumors by CLC is likely to be NK cells. The data indicate that large numbers of activated T cells cannot be detected in vivo and that in vitro induction of IL 2 receptors by lectin/antigen is necessary for the establishment of antigen-reactive T cell lines. In contrast, a proportion of LGL appear to be spontaneously activated and susceptible to IL 2-dependent growth. Thus, in the absence of stimulation, culture of unfractionated lymphoid cells in the presence of IL 2 is likely to select for the growth of LGL with NK activity.

Antibodies, Monoclonal↗

PubMed1978

[Responses of neurons in the cochlear nuclei of sharp-eared bats to presentation of frequency-modulated stimuli with a unidirectional change in frequency].

The investigation of the reactions of the neurons of the cochlear nuclei in the bats Myotis oxygnathus to frequency-modulated stimuli showed that the neurons with one best frequency (20%) have phasic responses while those with one or two best frequencies--tonic responses in the case when frequency of the stimulus changes from high to low frequencies.

Animals↗

PubMed1983

Frequency of mast cell precursors in normal tissues determined by an in vitro assay: antigen induces parallel increases in the frequency of P cell precursors and mast cells.

Persisting (P) cells, homogeneous populations of cells that grow in vitro for prolonged periods provided a specific growth factor is present, resemble mast cells in many respects. An in vitro assay based on limit dilution was used to determine the frequency of precursors capable of giving rise to P cells. The incidences of P cell precursors per 10(6) cells in tissues of CBA mice in representative experiments were as follows: bone marrow, 291; spleen, 30; mononuclear blood cells, 11; popliteal lymph node, 0.5; and mesenteric lymph node, 18. P cell precursors appeared to be relatively undifferentiated, non-granulated cells; no cells with metachromatically staining granules were detected in the bone marrow or peripheral blood. Furthermore, mice of the Wf/Wf genotype that were grossly deficient in mast cells had the same frequencies of P cell precursors in bone marrow and spleen as their normal +/+ littermates. In many tissues in which we found P cell precursors, pluripotential hemopoietic stem cells are present. Among nonepithelial cells from the gut mucosa, however, in which there was a 10-fold higher frequency of P cell precursors than in bone marrow cells, pluripotential hemopoietic stem cells were undetectable, indicating the existence of committed P cell precursors distinct from pluripotential hemopoietic stem cells. The frequency of P cell precursors in mesenteric lymph nodes was more than 30-fold higher than in the popliteal lymph nodes, suggesting that antigenic stimulation influences their numbers. This latter notion is supported by the observation that after immunization in the footpad, the number of P cell precursors in ipsilateral popliteal lymph nodes rose about 35-fold. Immunization was also accompanied by a rise in mast cell numbers in draining popliteal nodes. This correlation between P cell precursors and the local production of mast cells was strengthened by the observation that the frequency of P cell precursors in cells from the gut mucosa of mice of Wf/Wf genotype, which are unable to mount an intestinal mastocytosis, was more than 1000-fold lower than in wild type mice. Thus, the precursors of P cells and probably of at least the T cell-dependent subset of mast cells appear to be generated in the bone marrow and seed as non-granulated cells via the blood to peripheral tissues such as spleen, lymph node, and mucosal surfaces. P cells appear to be in vitro counterparts of the mucosal subset of mast cells.

Animals↗

PubMed1980

[Relation of sex and age to frequency of spontaneous chromosome aberrations in human peripheral blood lymphocytes. I. Age dynamics of the frequency of spontaneous chromosome aberrations and aberrant cells in peripheral blood lymphocytes].

Spontaneous frequency of chromosome aberrations in 680 individuals of both sex (from newborns to centenariants) has been studied. The age dependence of the frequency of chromosome aberrations has been revealed. The distribution of individuals according to the frequency of their chromosome aberrations corresponds to the Poisson's law. The analysis of the age dynamics of the frequency of chromosome aberrations made it possible to define three age periods. The first period involves the newborns with a high level of chromosome aberrations; the second period--individuals at the age of 1 to 20 years with the lowest level of aberrations; and the third one--individuals over 30 years old with continuous increase in the spontaneous frequency of chromosome aberrations with the age.

Adolescent↗

PubMed1987

Suppression of spontaneous breathing during high-frequency jet ventilation. Separate effects of lung volume and jet frequency.

The effect of ventilatory frequency of high-frequency jet ventilation (HFJV) from 1 to 5 Hz, apart from changes in thoracic volume, on spontaneous breathing activity was studied in Yorkshire piglets under pentobarbital anesthesia. The highest PaCO2 at which the animals did not breathe against the ventilator (apnea point) was established either by changing minute volume of ventilation or by adding CO2 to the respiratory gas. The higher the apnea point, the higher the suppression of spontaneous breathing activity was assumed to be. If the apnea point was searched for by changing minute volume a progressive increase of suppression of spontaneous respiratory activity was found at ventilatory rates of 3 Hz or more, concomitantly with a rise in end-expiratory pressure (PEE). In case the tidal volume was kept constant, increase of ventilatory rate resulted in a tremendous increase of lung volume, together with considerably higher levels of PEE. When under these conditions the apnea point was searched for by adding CO2 to the respiratory gas a much higher CO2-drive was needed for spontaneous breathing and therefore a much stronger inhibition of spontaneous breathing was concluded. By placing the animals in a body box in which pressure could be varied, thoracic volume could be kept constant during HFJV. When thoracic volume was kept constant in this way a constant tidal volume at increasing jet frequencies resulted in only a slight increase in suppression of spontaneous breathing. We conclude that the increase in lung volume is a major factor in suppressing central respiratory activity during HFJV. Jet frequency by itself might be an additional suppressive factor.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1996

Estimating minimum allele frequencies for DNA profile frequency estimates for PCR-based loci.

In order that there can be confidence that DNA profile frequency estimates will not place undue bias against a defendant, 2 methods are described for estimating minimum allele frequency bounds for PCR-based loci. One approach estimates minimum allele frequencies for VNTR and STR loci using sample size and the observed heterozygosity at a locus, while the second approach, appropriate for loci typed with allele-specific oligonucleotide probes, is based only on sample size. The use of a minimum allele frequency enables compensation for sparse sampling of infrequent alleles in population databases.

DNA Fingerprinting↗

PubMed1991

High frequency oscillatory ventilation near resonant frequency of the respiratory system in rabbits with normal and surfactant depleted lungs.

It has been suggested that high frequency oscillatory ventilation (HFV) might improve gas exchange and reduce the risk of pressure-related side-effects compared to conventional mechanical ventilation (CMV). Whereas most studies have used arbitrarily set frequencies for HFV, we evaluated the effects of HFV near resonant frequency (fr). Anaesthetised and tracheotomized adult rabbits (n = 10; 3.8-5.1 kg body weight) were ventilated by alternating periods of CMV and HFV near fr. Negative ventilator resistance was used for complete resistive unloading of the respiratory system before each HFV period. This enabled a continuous swinging at resonance thus allowing measurement of fr and selection of exactly that frequency for the HFV run. Intra-animal CMV-HFV comparisons (n = 4) were performed on each animal: with healthy lungs at a mean airway pressure (MAP) of 0.5 kPa and after saline lung lavage at MAPs of less than 1.5 kPa; 1.5-1.8 kPa; greater than 1.8 kPa. Surfactant removal caused total respiratory system compliance (Ctot) to decrease from 44 +/- 5 to 22 +/- 3 ml/kPa. Corresponding fr was 244 +/- 48 and 360 +/- 30 min-1, respectively. HFV produced effective pulmonary gas exchange but did not improve arterial oxygenation in comparison with CMV at matched MAPs both before and after surfactant depletion. Volume amplitudes of oscillation necessary to achieve normocapnia were slightly above the natural plus equipment (2 ml) dead space. Maximum intra-alveolar pressure (Pmax) was calculated for the HFV runs from MAP, Ctot, and the volume amplitude of oscillation. Pmax during CMV was nearly twice that during HFV at equivalent PaCO2 and equivalent MAPs throughout the experiments.

Animals↗

PubMed1999

Effect of frequency and tidal volume on pleural pressure in rabbits during high frequency ventilation.

Regional effects of the chest wall on airway pressure transmission were studied during high frequency ventilation in anesthetized rabbits. We measured airway pressure (Paw), esophageal pressure (Pes), and costal pleural pressure (Ppl) by a rib capsule and flow and volume with a calibrated pneumotachograph. Using a closed circuit, pressures and flow were measured at varying frequencies (2-80 Hz) and tidal volumes (2-20 ml). Mean Pes and Ppl increased with flow amplitude above 100-250 ml/s, whereas mean Paw decreased, consistent with air trapping. Paw, Pes, and Ppl amplitudes increased monotonically with flow amplitude except above 400-500 ml/s, where the Ppl amplitude decreased suddenly. The latter occurring simultaneously with a sudden fall in mean Paw indicated airway flow limitation in costal regions. Flow instabilities during flow limitation were consistent with the large increase in the phase difference between Paw and Ppl and its variability, with frequency. By contrast, the phase difference between Paw and Pes and its variability were relatively small. These differences in Pes from Ppl responses might be caused by a difference in the impedance of the airway-mediastinum pathway or a direct transmission of tracheal pressure oscillations to the esophagus. The former suggests that constraints offered by the mediastinum and rib cage resulted in nonuniform ventilation during high frequency ventilation.

Animals↗