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PubMed1990

Analysis of 228Ra and 226Ra in public water supplies by a gamma-ray spectrometer.

Methods for measuring 228Ra were reviewed to select a brief and simple screening procedure under NIPDW Regulations for public water supplies. A two-step method was considered to concentrate Ra by evaporation or co-precipitation and to count it with a gas ionization detector, a liquid-scintillation detector, or a Ge detector with multichannel analyzer. Gross beta particle counting appears to be feasible for screening to meet the 0.04 Bq L-1 detection limit. One can utilize the same sample volume as currently collected and measure radiation with commonly available equipment in reasonable time. The required sample volumes were estimated on the basis of known counting efficiencies and background count rates. Gamma-ray spectral analysis is the recommended option, however, because 226Ra and 228Ra can be determined directly and simultaneously. Several aspects of the method were examined to assure that the concentration procedure is nearly quantitative and that the detection limit can be reached with a 3.8-L sample in a 6000-s counting period. The method was tested with Ra tracer solutions and EPA intercomparison samples over the range of 0.04 to 1 Bq L-1. It was found appropriate for 228Ra and 226Ra analyses.

Radium↗

PubMed1969

Computer analysis of the leaf movements of pinto beans.

Computer analysis was used for the detection of rhythmic components and the estimation of period length in leaf movement records. The results of this study indicated that spectral analysis can be profitably used to determine rhythmic components in leaf movements.In Pinto bean plants (Phaseolus vulgaris L.) grown for 28 days under continuous light of 750 ft-c and at a constant temperature of 28 degrees , there was only 1 highly significant rhythmic component in the leaf movements. The period of this rhythm was 27.3 hr. In plants grown at 20 degrees , there were 2 highly significant rhythmic components: 1 of 13.8 hr and a much stronger 1 of 27.3 hr. At 15 degrees , the highly significant rhythmic components were also 27.3 and 13.8 hr in length but were of equal intensity. Random movements less than 9 hr in length became very pronounced at this temperature. At 10 degrees , no significant rhythm was found in the leaf movements. At 5 degrees , the leaf movements ceased within 1 day.

Journal Article↗

PubMed1998

Submicrometre-area high-energy-resolution photoelectron spectroscopy system.

A submicrometre-area photoelectron spectroscopy system that uses a multi-layer-coated Schwarzschild objective as the soft X-ray microbeam optics has been developed. The system is located at an undulator beamline (BL-16U) at the Photon Factory in the High Energy Accelerator Research Organization. By knife-edge measurement, the microbeam size was estimated to be 160 nm at the sample position using a 25-75% criterion. Photoelectron spectral measurements revealed that the Fermi edge width was 0.12 eV, which means that the instrumental resolution was 0.05 eV, after removing the natural broadening of the Fermi edge at room temperature. This system offers both high energy resolution and high spatial resolution.

Journal Article↗

PubMed2004

In vivo 31P NMR spectroscopy shows an increase in glycerophosphorylcholine concentration without alterations in mitochondrial function in the prefrontal cortex of medicated schizophrenic patients at rest.

The (31)P NMR localised method was used to study the metabolism of phospholipid and high energy phosphate in the prefrontal cortex. The spectra were taken from patients with schizophrenia (11 males) receiving neuroleptic medication, and were compared to normal controls (15 males). Their spectral intensities were analysed using a non-linear least-squares method with a prior knowledge of the fixed chemical shifts and linewidths, leading to further resolution into resonances of glycerophosphorylethanolamine (GPE), glycerophosphorylcholine (GPC), phosphorylethanolamine (PE) and phosphorylcholine (PC). The metabolite concentrations were calculated referring to the spectral intensities of phosphate phantoms with known concentrations. T1 values of phantom and cerebrum were estimated from a series of localised inversion recovery spectra to correct for the signal saturation effects. The schizophrenic patients showed an increased concentration of GPC but not GPE, PE or PC. Furthermore, no difference was observed regarding the concentration of high-energy phosphates such as phosphocreatine, inorganic phosphate and ATP. The patients did not show any differences in mitochondrial function such as phosphorylation potential and the ratio of the rate of ATP synthesis. Thus, an increase in GPC concentration in the prefrontal cortex could be characteristic of the pathophysiology of schizophrenia with mild negative symptoms.

Adult↗

PubMed1999

Level discrimination of single tones in a multitone complex by normal-hearing and hearing-impaired listeners.

A conditional-on-a-single-stimulus (COSS) analysis procedure [B. G. Berg, J. Acoust. Soc. Am. 86, 1743-1746 (1989)] was used to estimate how well normal-hearing and hearing-impaired listeners selectively attend to individual spectral components of a broadband signal in a level discrimination task. On each trial, two multitone complexes consisting of six octave frequencies from 250 to 8000 Hz were presented to listeners. The levels of the individual tones were chosen independently and at random on each presentation. The target tone was selected, within a block of trials, as the 250-, 1000-, or 4000-Hz component. On each trial, listeners were asked to indicate which of the two complex sounds contained the higher level target. As a group, normal-hearing listeners exhibited greater selectivity than hearing-impaired listeners to the 250-Hz target, while hearing-impaired listeners showed greater selectivity than normal-hearing listeners to the 4000-Hz target, which is in the region of their hearing loss. Both groups of listeners displayed large variability in their ability to selectively weight the 1000-Hz target. Trial-by-trial analysis showed a decrease in weighting efficiency with increasing frequency for normal-hearing listeners, but a relatively constant weighting efficiency across frequency for hearing-impaired listeners. Interestingly, hearing-impaired listeners selectively weighted the 4000-Hz target, which was in the region of their hearing loss, more efficiently than did the normal-hearing listeners.

Adult↗

PubMed1982

Acquired pendular nystagmus: its characteristics, localising value and pathophysiology.

Investigations were made of 16 patients with acquired pendular nystagmus and a further 32 cases reported in the literature were reviewed. Amongst our own patients two thirds had multiple sclerosis, almost one third a cerebrovascular accident or angioma and two had optic atrophy with squint. The nystagmus took forms which could be monocular or binocular, conjugate or disconjugate and could involve movements about single or multiple axes. Spectral analysis was used to characterise the amplitude and frequency of the movements and to estimate the degree of relationship (coherence) between movements of the two eyes or between movements of one eye about several axes. The oscillations ranged in frequency from 2·5 Hz to 6 Hz, with typical amplitudes between 3° and 5°. In a given patient all oscillations, regardless of plane, were highly synchronised. Somatic tremors of the upper limb, face and palate associated with the nystagmus were often at similar frequencies to the eye movement. The other ocular signs common to all our patients were the presence of squint with failure of convergence. Most patients also had skew deviation or internuclear ophthalmoplegia or both. The major oculomotor systems, that is, saccades, pursuit, optokinetic and vestibulo-ocular reflexes could be intact. It is inferred that the mechanism responsible for the pendular nystagmus lies at a level which is close to the oculomotor nuclei so that it can have monocular effects but is not part of the primary motor pathways. It is possible that this mechanism normally subserves maintenance of conjugate movement and posture of the eyes. The periodicity of the nystagmus is likely to arise from instability in a certain type(s) of neurone, for the associated somatic tremors have similar characteristics and yet involve very different neuronal muscular circuitry. Prognosis for cessation of the nystagmus is poor. In five patients with multiple sclerosis it was suppressed by intravenous hyoscine with, however, unacceptable subsequent side effects.

Adult↗

PubMed1998

Deterioration of cerebral autoregulation during orthostatic stress: insights from the frequency domain.

To determine whether dynamic cerebral autoregulation is impaired during orthostatic stress, cerebral blood flow (CBF) velocity in the middle cerebral artery (transcranial Doppler) and mean arterial pressure (MAP; Finapres) were measured continuously in 12 healthy subjects during ramped maximal lower body negative pressure (LBNP) to presyncope. Velocity and pressure were averaged over 6-min periods of stable data at rest and during LBNP to examine steady-state cerebral hemodynamics. Beat-to-beat variability of velocity and pressure were quantified by a "variation index" (oscillatory amplitude/steady-state mean value) and by power spectral analysis. The dynamic relationship between changes in pressure and velocity was evaluated by the estimates of transfer and coherence function. The results of the study were as follows. Steady-state MAP remained relatively constant during LBNP, whereas CBF velocity decreased progressively by 6, 15, and 21% at -30, -40, and -50 mmHg LBNP, respectively (P < 0.05 compared with baseline). At the maximal level of LBNP (30 s before presyncope) MAP decreased by 9.4% in association with a prominent reduction in velocity by 24% (P < 0.05 compared with baseline). The variation index of pressure increased significantly from 3.8 +/- 0.3% at baseline to 4.5 +/- 0. 6% at -50 mmHg LBNP in association with an increase in the variation index of velocity from 6.0 +/- 0.6 to 8.4 +/- 0.7% (P < 0.05). Consistently, the low- (0.07-0.20 Hz) and high-frequency (0.20-0.30 Hz) power of variations in pressure and velocity increased significantly at high levels of LBNP (P < 0.05) in association with an increase in transfer function gain (24% at -50 mmHg, P < 0.05). We conclude that the damping effects of autoregulation on variations in CBF velocity are diminished during orthostatic stress in association with substantial falls in steady-state CBF velocity. We suggest that these changes may contribute in part to the development of presyncope.

Adult↗

PubMed2004

Absorption and scattering imaging of tissue with steady-state second-differential spectral-analysis tomography.

A novel approach to reconstructing both the absorption and the scattering properties of a turbid medium simultaneously from steady-state broadband spectral measurements is presented that utilizes second-differential fitting to the water spectrum to estimate the optical path length in tissue. Theoretical and experimental evidence is provided to demonstrate the robust accuracy of the spectroscopy approach and reconstructed absorption images. The steady-state broadband CCD system has the potential to provide accurate chromophore imaging without the technological complexity of time- or frequency-domain systems.

Absorption↗

PubMed2001

Confocal analysis of phosphatidylserine externalization with the use of biotinylated annexin V revealed with streptavidin-FITC, -europium, -phycoerythrin or -Texas Red in oxysterol-treated apoptotic cells.

OBJECTIVE: To analyze externalization of phosphatidylserine via annexin V on apoptotic cells by laser scanning confocal microscopy and factor analysis of biomedical image sequences (FAMIS). STUDY DESIGN: Streptavidin-fluorescein isothiocyanate (FITC), -europium (Eu), -phycoerythrin (PE) and -Texas Red (TR) were chosen to reveal the binding of biotinylated annexin V on apoptotic U937 human leukemic cells and ECV-304 human endothelial cells induced under treatment with 7-ketocholesterol or 7 beta-hydroxycholesterol. Excitation of each fluorochrome was obtained by selection of specific lines (351 + 364 nm, 488 nm) of the argon laser of a confocal microscope. Temporal and spectral series were performed to characterize each fluorochrome. FAMIS was applied to these series to estimate images corresponding to stains. RESULTS: Each fluorochrome was clearly distinguished, and images showed localization of phosphatidylserine, which was improved by image analysis. CONCLUSION: On apoptotic cells it is possible to analyze differences in the improved visualization of phosphatidylserine in series processed by FAMIS with the use of biotinylated annexin V revealed with streptavidin-FITC, -Eu, -PE or -TR.

Annexin A5↗

PubMed1991

Power spectrum analyses of electromyographic activity. Discriminators in the differential assessment of patients with chronic low-back pain.

Some parameters of the electromyographic power spectrum of the paraspinal muscles were recorded and analyzed with regard to their ability to discriminate between normal controls and patients with back pain classified as "avoiders" or "confronters" by their responses to the Pain Behavior Checklist. In terms of the activity of the multifidus muscle, the avoider group displayed spectral changes towards lower frequencies, reduced variability in the density spectrum, and higher values of estimated initial frequencies. Measures of the activity of the iliocostalis lumborum did not contribute in any significant way to these group differences. Based on these findings, and on the available literature concerning the histology and physiology of paraspinal muscles, it is proposed that the observed characteristics of the avoider group may be due to a reduced ratio of slow twitch to fast twitch muscle fibers in the multifidus.

Back Pain↗

PubMed1997

Comparative pharmacokinetics and pharmacodynamics of remifentanil, its principle metabolite (GR90291) and alfentanil in dogs.

Remifentanil is an esterase-metabolized opioid developed for use in anesthesia. The principal metabolite of remifentanil, GR90291, is considered to be less potent. This study determined the relative potency of GR90291 and alfentanil, compared with remifentanil, in anesthetized dogs. Male dogs received thiamylal sodium, and anesthesia was maintained using isoflurane and N2O in oxygen. Each dog received a 5-min infusion of 0.5 microg/kg/min remifentanil, 500 microg/kg/min GR90291 and 1.6 mg/kg/min alfentanil in random order, separated by 1 week. Serial blood samples were collected during and after the infusion. The electroencephalogram was evaluated using aperiodic analysis. The pharmacokinetics and pharmacodynamics of remifentanil, GR90291 and alfentanil were determined using nonlinear least-squares regression analysis. Remifentanil was rapidly eliminated, with a terminal half-life of 6 min, compared with 19 min for GR90291 and alfentanil. Using the estimated concentration that elicits 50% of the maximum response (EC50) for delta EEG activity and spectral edge95, remifentanil was 4213 to 4637 times more potent than GR90291 and 7.7 to 8.5 times more potent than alfentanil. The blood-brain equilibration half-life was 2.3 to 5.2 min for remifentanil, 0.39 to 0.41 min for GR90291 and 3.1 to 3.7 min for alfentanil.

Alfentanil↗

PubMed2004

Bandwidth of spectral resolution for two-formant synthetic vowels and two-tone complex signals.

Spectral integration refers to the summation of activity beyond the bandwidth of the peripheral auditory filter. Several experimental lines have sought to determine the bandwidth of this "supracritical" band phenomenon. This paper reports on two experiments which tested the limit on spectral integration in the same listeners. Experiment I verified the critical separation of 3.5 bark in two-formant synthetic vowels as advocated by the center-of-gravity (COG) hypothesis. According to the COG effect, two formants are integrated into a single perceived peak if their separation does not exceed approximately 3.5 bark. With several modifications to the methods of a classic COG matching task, the present listeners responded to changes in pitch in two-formant synthetic vowels, not estimating their phonetic quality. By changing the amplitude ratio of the formants, the frequency of the perceived peak was closer to that of the stronger formant. This COG effect disappeared with larger formant separation. In a second experiment, auditory spectral resolution bandwidths were measured for the same listeners using common-envelope, two-tone complex signals. Results showed that the limits of spectral averaging in two-formant vowels and two-tone spectral resolution bandwidth were related for two of the three listeners. The third failed to perform the discrimination task. For the two subjects who completed both tasks, the results suggest that the critical region in vowel task and the complex-tone discriminability estimates are linked to a common mechanism, i.e., to an auditory spectral resolving power. A signal-processing model is proposed to predict the COG effect in two-formant synthetic vowels. The model introduces two modifications to Hermansky's [J. Acoust. Soc. Am. 87, 1738-1752 (1990)] perceptual linear predictive (PLP) model. The model predictions are generally compatible with the present experimental results and with the predictions of several earlier models accounting for the COG effect.

Acoustic Stimulation↗

PubMed1988

High-resolution 1H NMR spectral signature from human atheroma.

Coronary artery disease due to atherosclerosis takes the lives of approximately 550,000 Americans each year--an enormous toll. Put in economic terms, the cost to the United States alone has been estimated to exceed 60 billion dollars annually. We have found that well-resolved proton (1H) NMR spectra can be obtained from human atheroma (fatty plaque), despite its macroscopic solid appearance. The fraction of the total spectral intensity corresponding to the sharp 1H NMR signals is temperature dependent and approaches unity at body temperature (37 degrees C). Studies of the total lipids extracted from atheroma and cholesteryl esters were conducted to identify the chemical and physical origin of the spectral signature. The samples were characterized through assignment of their chemical shifts and by measurement of their T1 and T2 relaxation times as a function of magnetic field strength. The results suggest that the relatively sharp 1H NMR signals from human atheroma (excluding water) are due to a mixture of cholesteryl esters, whose liquid-crystalline to isotropic fluid phase transition is near body temperature. Preliminary applications to NMR imaging of human atheroma are reported, which demonstrate early fatty plaque formation within the wall of the aorta. These findings offer a basis for noninvasive imaging by NMR to monitor early and potentially reversible stages of human atherogenesis.

Aorta↗

PubMed2002

Bispectral index monitoring during electroconvulsive therapy under propofol anaesthesia.

BACKGROUND: The accuracy of the bispectral index (BIS) as a monitor of consciousness has not been well studied in patients who have abnormal electroencephalograms (EEG). METHODS: We studied the changes in BIS, its subparameters, and spectral entropy of the EEG during 18 electroconvulsive treatments under propofol and succinylcholine anaesthesia. A single bifrontal EEG, and second subocular channel (for eye movement estimation) was recorded. RESULTS: The median (interquartile range) BIS value at re-awakening was only 57 (47-78)--thus more than a quarter of the patients woke at BIS values of less than 50. The changes in spectral entropy values were similar: 0.84 (0.68-0.99) at the start, 0.65 (0.42-0.88) at the point of loss-of-consciousness, 0.63 (0.47-0.79) during the seizures, and 0.58 (0.31-0.85) at awakening. CONCLUSIONS: Post-ictal slow-wave activity in the EEG (acting via the SynchFastSlow subparameter) may cause low BIS values that do not correspond to the patient's clinical level of consciousness. This may be important in the interpretation of the BIS in other groups of patients who have increased delta-band power in their EEG.

Adult↗

PubMed1990

Spectral comparison of solar simulators and sunlight.

In evaluating sunscreen efficacy, spectral distribution of the irradiation sources can influence the sun protection factor (SPF). The purpose of this investigation was to examine the uniformity of ultraviolet (UV) spectral irradiance of solar simulators used in various SPF testing laboratories, compare them with natural sunlight UV radiation (UVR), and recommend performance limits to ensure that the variability of radiation sources in the UVB region minimally affects SPF estimates. The critical portion of the solar erythemogenic spectrum was identified as the UVB portion, defined as the region between 280 and 320 nm. The spectral irradiance of 26 solar simulators and other UV sources was measured and compared with a summer noon solar spectrum measured in Albuquerque, NM. Proposed spectral limits were developed as a 6-nm "acceptance band" centered on this standard spectrum normalized at 320 nm. The results indicated that the xenon-arc solar simulators currently used in the United States in testing sunscreens either meet the proposed standard solar spectrum or can be readily modified with available UV filters to meet this standard. The devices that have spectral characteristics not resembling sunlight fail to meet the proposed standard and should not be used for sunscreen SPF testing.

Filtration↗

PubMed1991

Spectral weights and the profile bowl.

In these experiments, listeners detected changes in the shape of a complex spectrum that varied in overall level. With multicomponent complexes, a typical finding is that the listeners were more sensitive to changes made in the middle components of the spectrum than to changes made at either edge. We used a technique developed by Berg (1989) to estimate the weight listeners attached to the different components of the spectrum in making these judgements. For reasons not understood, the pattern of spectral weights was nearly optimum for a change made in the middle component of the spectrum and much poorer when the change occurred at either edge.

Attention↗

PubMed1998

Firing properties of olfactory bulb neurons during sniffing in rats.

Single unit activities from the olfactory bulb were recorded during sniffing in unanesthetized rats. Spectral analyses by the Walsh transform were applied to the spike trains of units. In addition, inter-spike intervals (ISIs) were measured to estimate post-spike excitability and serial correlations. The modulation of firing due to respiration cycles was observed only in four units (10%). Thirty-three units (82.5%) displayed low-frequency fluctuations such as 1/f noise in spike density. Their spectral density for the low-frequency range was inversely proportional to the frequency, to the power of 0.08-0.55. These units also showed "hyper-recovery" in post-spike excitability. In addition, the first-order serial correlation of ISIs was significantly positive in 36 units (90%). The degree of 1/f fluctuation was significantly correlated with the amplitude of "hyper-recovery" in post-spike excitability and with the serial correlation coefficient. To test the hypothesis that the self-facilitation of a neuron causes 1/f fluctuations in its spike trains, simulations of single neuron activity with self-facilitation were performed using an integrate-and-fire neuron model, and its spike trains were analyzed. The model neuron with self-facilitation mimicked the characteristics observed in olfactory bulb neurons such as 1/f fluctuations in spike density, positive correlations between successive ISIs and "hyper-recovery" in post-spike excitability. These results suggest that olfactory bulb neurons have a mechanism for self-facilitation causing 1/f fluctuations in spike density.

Algorithms↗

PubMedDate not supplied

Optimal smoothing of coherence estimates.

We have previously described the usefulness of the magnitude-squared coherence function in analysis of auditory evoked potentials (AEPs) (Ear Hear., 1989, 20: 2-13). For each frequency of interest, the coherence value can be compared to a 'critical value' to determine whether a response is present. Coherence functions must be smoothed across either multiple subaverages or adjacent frequencies (or both) to be reliable, but there are trade-offs: increasing the degree of smoothing increases computational time and (in the case of frequency smoothing) reduces spectral resolution. Using AEPs to clicks and amplitude-modulated tones we investigated the effects of variable degrees of smoothing on threshold estimates in 10 normal human subjects. Thresholds were found to be lower for coherence estimates than for visual detection and are also lower for longer data collection periods. However, there appears to be little if any advantage to segment smoothing beyond 8-16 subaverages. The optimal degree of frequency smoothing is more difficult to specify, depending on the spectrum of the AEP being analyzed (especially the rate of change of phase), and the spectral resolution of the analysis system.

Acoustic Stimulation↗