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At least 73 records · Page 4Linked to original sources
PubMed1991

Single particle tracking. Analysis of diffusion and flow in two-dimensional systems.

Analysis of the trajectories of small particles at high spatial and temporal resolution using video enhanced contrast microscopy provides a powerful approach to characterizing the mechanisms of particle motion in living cells and in other systems. We present here the theoretical basis for the analysis of these trajectories for particles undergoing random diffusion and/or systematic transport at uniform velocity in two-dimensional systems. The single particle tracking method, based on observations of the trajectories of individual particles, is compared with methods that characterize the motions of a large collection of particles such as fluorescence photobleaching recovery. Determination of diffusion coefficients or transport velocities either from correlation of positions or of velocities of the particles is discussed. A result of practical importance is an analysis of the dependence of the expected statistical uncertainty of these determinations on the number of position measurements. This provides a way of judging the accuracy of the diffusion coefficients and transport velocities obtained using this approach.

Diffusion↗
PubMed1992

Facilitation of agonist motoneurons upon initiation of rapid and slow voluntary movements in man.

The time course of facilitation of the agonist motoneurons upon initiation of voluntary ankle dorsiflexion was investigated in eight healthy subjects. The H-reflex and visually guided tracking methods were used for testing the excitability of the motoneuron pool and for controlling the initiation of movement as well as speed and force. Since the onset of voluntary EMG activity (EMG reaction time: EMGvRT) was delayed and/or obscured by test H-reflexes which were evoked very close to the behavioral responses, the subject was instructed to make response movements bilaterally, and EMGvRT was measured on the side without stimulation. In every subject, the EMGvRT was invariably longer in the ramp movement than in the step movement. The onset of H-reflex facilitation prior to EMG onset, which was regarded as indicating the arrival time of the descending motor command to the motoneuron pool, always started earlier in the ramp movement than in the step movement. The difference in facilitation onset between the two tasks was smaller than that in EMGvRT. Since the amplitude of the H-reflex at the onset of the voluntary EMG was equivalent in both movements, the development of H-reflex towards the behavioral EMG onset was more gradual in the ramp movement than in the step movement. The present results demonstrate that the longer reaction time in the slow ramp task depends on 2 factors: delay in the arrival of descending facilitatory impulses to the agonist motoneuron pool, and its slow recruitment thereafter.

Adult↗
PubMed1983

Demonstration of presbycusis across repeated measures in a nonhuman primate species.

The progress of age-related hearing loss in three 31-yr-old, two 24-yr-old, and two 9-yr-old rhesus monkeys (Macaca mulatta) was repeatedly examined over a period of 3 yr. Pure-tone audiograms for seven frequencies, .125, .500, 2.000, 4.000, 16.000, 22.667, and 32.000 kHz, were obtained through the use of the psychophysical tracking method. Analysis indicated the presence of presbycusis in the older animals. Animals demonstrating presbycusis showed a progressive decrement in the ability to detect higher frequencies and an overall hearing loss at all frequencies.

Aging↗
PubMed1978

Effects of stimulus duration and stimulus off time on the auditory and acoustic reflex thresholds.

The effects of stimulus duration and stimulus off time on the thresholds of hearing and the acoustic reflex were investigated in 10 normal-hearing subjects and 10 subjects with sensorineural hearing loss. A 1000-Hz stimulus with on-off times of 500-500 msec and 30-30 msec was used to obtain hearing sensitivity and acoustic reflex thresholds via a tracking method. Auditory threshold was poorer for the 30-30 msec tone than the 500-500 msec stimulus in both groups. Using the different stimuli, no significant difference in acoustic reflex threshold was observed in either group. These results suggest that the addition of a short off time modifies the previously observed effects of both duration and off time on the acoustic reflex and auditory threshold.

Adult↗
PubMed1987

Evaluation of sepsis in a critically ill surgical population.

We report a new clinical rating system which assesses septic patients' ongoing disease course and its severity. Our system incorporates the Therapeutic Intervention Scoring System (TISS) and Acute Physiology and Chronic Health Evaluation to measure discrete organ system abnormalities, plus a multiple system organ failure scale to quantify the number of abnormal organ systems. The resulting score, which reflects the severity of multiple organ dysfunction and grades responsiveness to therapy, was validated against the actual disease course. Retrospective and prospective profiles of individual surgical ICU patients demonstrated that this tracking method was a more effective indicator of severity of sepsis and more sensitive to the day-to-day changes in clinical status than either the TISS or APACHE II components alone. We also demonstrate that a graphic illustration of daily system scores yields clinically useful information relevant to the patients' septic course.

Bacterial Infections↗
PubMed1986

Poststenotic flow disturbance in the dog aorta as measured with pulsed Doppler ultrasound.

Blood flow velocity was measured in the dog aorta distal to mechanically induced constrictions of various degrees of severity employing an 8-MHz pulsed Doppler ultrasound velocimeter and a phase-lock loop frequency tracking method for extracting velocity from the Doppler quadrature signals. The data were analyzed to construct ensemble average velocity waveforms and random velocity disturbances. In any individual animal the effect of increasing the degree of stenosis beyond approximately 25 percent area reduction was to produce increasing levels of random velocity disturbance. However, variability among animals was such that the sensitivity of random behavior to the degree of stenosis was degraded to the point that it appears difficult to employ Doppler ultrasound measurements of random disturbances to discriminate among stenoses with area reductions less than approximately 75 percent. On the other hand, coherent vortex structures in velocity waveforms consistently occurred distal to mild constrictions (25-50 percent area reduction). Comparison of the phase-lock loop Doppler ultrasound data with simultaneous measurements using invasive hot-film anemometry, which possesses excellent frequency response, demonstrates that the ultrasound method can reliably detect those flow phenomena in such cases. Thus, the identification of coherent, rather than random, flow disturbances may offer improved diagnostic capability for noninvasively detecting arteriosclerotic plaques at relatively early stages of development.

Animals↗
PubMed1982

Inverse frequency dependence of simultaneous tone-on-tone masking patterns at low levels.

Using the Békésy tracking method, tone-on-tone masking patterns were measured with eight subjects at eight masker frequencies between 250 Hz and 6.03 kHz. Masking patterns were obtained for five masker levels between 20 and 60 dB SPL. Test-tone frequencies were chosen within two critical bands above and below the masker frequency. A level-dependent frequency asymmetry of masking was observed at all masker frequencies except at 250 Hz. At low levels there was a greater spread of masking towards the lower frequencies than toward the higher frequencies, but at high levels there was a greater spread of masking towards the higher frequencies than toward the lower frequencies. Only at masker levels of 40 dB SPL were the masking patterns approximately symmetrical.

Auditory Threshold↗
PubMed1984

Receiving beam patterns and directivity indices of the Atlantic bottlenose dolphin Tursiops truncatus.

The receiving beam patterns of an Atlantic bottlenose dolphin was measured in both the vertical and horizontal planes for frequencies of 30, 60, and 120 kHz. Measurements in the vertical plane were performed by training the dolphin to rotate on its side and station on a vertically oriented biteplate device. A signal source was positioned 3.5 m directly in front of the animal on an arc while the position of a broadband noise source was varied in azimuth along the arc, with the animal stationed at the origin of the arc. Using a go/no-go response procedure, the masked threshold of the dolphin was determined by varying the intensity of the noise source via a tracking method of stimulus presentation, for different azimuth's of the noise source. Measurements in the horizontal plane were obtained with the dolphin stationing on a horizontal biteplate. Two masking noise sources, projecting equal levels of uncorrelated noise, were located at +/- 20 degrees on either side of the arc midpoint. The levels of the noise source were held constant and the masked thresholds determined by varying the level of the signal source while positioned at different azimuths along the arc. Results indicated that maximum sensitivity in the vertical plane (the major axis of the beam) occurred between 5 degrees and 10 degrees above the midline of the animal's mouth and that the beam patterns were not symmetrical about the major axis. The sensitivity dropped off more quickly with increasing angle above the head than below. The beam patterns in the horizontal plane were directed forward and were fairly symmetrical about the midline of the animal's body.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Individual differences in auditory capabilities. I.

Twenty-eight audiometrically normal adult listeners were given a variety of auditory tests, ranging from quiet and masked thresholds through the discrimination of simple and moderately complex temporal patterns. Test-retest reliability was good. Individual differences persisted on a variety of psychoacoustic tasks following a period of training using adaptive threshold-tracking methods, and with trial-by-trial feedback. Large individual differences in performance on temporal-sequence-discrimination tasks suggest that this form of temporal processing may be of clinical significance. In addition, high correlations were obtained within given classes of tests (as, between all tests of frequency discrimination) and between certain classes of tests (as, between tests of frequency discrimination and those of sequence discrimination). Patterns of individual differences were found which support the conclusion that individual differences in auditory performance are, in part, a function of patterns of independent abilities.

Adolescent↗
PubMed1977

A simultaneous discrimination procedure for the measurement of vision in nonverbal children.

Few nonverbal developmentally disabled children ever receive adequate vision assessment because of their limited language skills. The present study details a simultaneous discrimination procedure for measuring subjective visual acuity in such children. A stimulus fading procedure was used to train a discrimination between Snellen Es differing in orientation, and a psychophysical tracking method was used to determine acuity thresholds. The procedure was tested with 11 nonverbal autistic and schizophrenic children and validated with four nonpsychotic children. Eight of the psychotic children were successfully examined in one to three sessions. Two of these children were identified as having significant acuity losses. The validity assessment showed that the experimental procedure resulted in thresholds equal to or slightly lower than those obtained with the Illiterate E chart.

Adolescent↗
PubMed1989

MR angiography and dynamic flow evaluation of the portal venous system.

We studied the value of MR angiographic techniques in imaging the portal venous system. Projection angiograms were created by postprocessing a series of two-dimensional, flow-compensated gradient-echo images. Flow velocity was determined by a bolus-tracking method with radiofrequency tagging and multiple data readout periods. Each image was acquired during a breath-hold. MR angiography was applied to six normal subjects and four patients with abnormal hemodynamics in the portal venous system. Flow velocity determined by MR was correlated with the results of duplex sonography. The main portal vein and intrahepatic branches were shown in all cases. Portosystemic collaterals were identified in all patients with portal hypertension. In normal subjects, peak flow velocities (17.9 +/- 2.8 cm/sec) on MR correlated well with values determined by duplex sonography (17.5 +/- 2.2 cm/sec) (r = .846, p less than .04). Reversed portal blood flow was shown in two patients. One patient with portal vein thrombosis had no evidence of flow by MR angiography. Our results indicate that MR angiography can provide a three-dimensional display of normal and abnormal vascular anatomy as well as functional information in the portal venous system.

Blood Flow Velocity↗
PubMed1982

Uranium content in porcelain denture teeth and in porcelain powders for ceramic crowns.

Some porcelain denture teeth and porcelain powders marketed in Sweden haven been analyzed for the content of uranium. The fission track method and the delayed neutron technique were the methods used. Compared to results published previously the content of uranium was generally found to be lower in the brands analyzed. The denture teeth contained 23-186 ppm for Anatoform, 35-137 ppm for Myerson, 15-45 ppm for Candulor G and 20-53 ppm for Vivopearl. The baked and fired porcelain powders showed values of about 2.8 ppm at most, those in the form of powder about 25 ppm at most. The radiation dose to the mucosa of the upper lip was calculated and is discussed.

Crowns↗
PubMed1986

Concentration and particle-size distribution of uranium and some trace elements in airborne dust collected in Tsukuba.

Uranium and some other trace elements were determined in the size-separated airborne dust collected in Tsukuba with an Andersen-type high-volume cascade impactor. The fission track method and the instrumental neutron activation method were applied to the determination of uranium and other elements, respectively. Selenium, antimony, arsenic and zinc were found to be rich in particulates of smaller size, while scandium, iron and cobalt showed a reverse trend, depending on their main origins, i.e. whether industrial or terrestrial. Uranium was distributed in both the larger and smaller particles to the same extent, suggesting that it is derived from both the terrestrial and artificial sources.

Dust↗
PubMed1987

Distribution of uranium in human lungs.

Several human lung samples were dissected into lobes and uranium and silicon contents in each lobe were determined by the fission track method and the inductively coupled plasma-atomic emission spectrometry (ICP-AES), respectively. It was found that both uranium and silicon concentrations were high in the upper lobe compared with those in the lower one. Though the tendency may be mainly interpreted by the deposition way of airborne dust in the lung, the higher U/Si concentration ratio in the upper part than that in the lower part of lungs may suggest the partial removal of uranium deposited in the lower part of the tissue.

Air Pollution, Radioactive↗
PubMed1987

Distribution of uranium in human bones.

Uranium and calcium contents in human bones (skull, rib and femur) were determined by the fission track method and the inductively coupled plasma-atomic emission spectroscopic method (ICP-AES), respectively. The U/Ca concentration ratio in the bones was found to decrease in the order of rib greater than femur greater than skull, which is in accordance with the decreasing order of the mean annual replacement percentage of bone components. Several femur bones were cut into several longitudinal segments, and uranium and calcium contents in each segment were determined. Among these, the U/Ca ratio in the epiphysis was higher than those in the diaphysis.

Adult↗
PubMed1987

Plutonium and uranium in Japanese human tissues.

Plutonium and uranium in human tissues obtained from residents of the Tokyo area were determined by a-spectrometry and the fission track method, respectively. The distribution pattern of each element was estimated on the basis of mean concentration obtained. Plutonium is concentrated in some special organs, while uranium is distributed rather generally throughout the whole body. This difference of distribution tendency is considered to be due to the characteristics of stable chemical states of the elements in body fluid; Pu4+ for plutonium and UO2(2+) for uranium.

Asian People↗
PubMedDate not supplied

Biocybernetic investigations of pursuit and posture motor control--a strategy for a detailed characterization of movement disorders in brain-damaged children.

By means of a biocybernetic approach the pursuit and posture motor control of brain-damaged children with spastic hemiparesis and disturbed motor coordination of mild extent were investigated. The postural motor control system was loaded by pseudostochastic binary torque sequences applied to the wrist. The dynamics of this system were characterized on the basis of the parameters forearm displacement as well as surface-EMG of M. Biceps and Triceps (calculations of weight functions). The pursuit motor control was analyzed by a pursuit tracking method. By this way the motor capacity for fine and rough motor coordination, motor rhythm, motor adaptation, the maximal speed of movements and motor reaction time could be tested. Considering these results a characterization of movement control on different levels of motor regulation was possible (dynamics of muscular, spinal, and supraspinal components of motor control).

Brain Damage, Chronic↗