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PubMed1995

Advances in processing of surface myoelectric signals: Part 2.

The paper focuses on the analysis of myoelectric evoked potentials and their progressive scaling, as well as morphological changes using orthogonal basis functions with essentially finite time support; and the compression of the information content using principal component analysis. The application of the Hermite-Rodriguez and the associated Hermite functions is discussed as a means to provide compact information about the shape of the M-wave or of the power spectral density function of either voluntary or electrically elicited myoelectric signals; a means to estimate scaling factors; and a means to describe and classify nonstationarities. The principal component analysis shows the possibility of a compression ratio of at least 10:1 in the storage of M-wave sequences. The paper also describes three methods for the estimation of delay between similar signals, and therefore for estimation of conduction velocity. They are based on normalised integrals. Fourier transform matching and matching in the time domain. In particular conditions they provide different results for the same pair of signals. The concept of delay and the performance of these methods are reviewed and discussed. The paper is not exhaustive. It has the main objective of making the reader aware of the wealth of methods available for nonstationary myoelectric signal analysis and conduction velocity estimation, and of the need to use them with knowledge of their respective advantages, disadvantages, peculiarities and limitations.

Electric Stimulation↗
PubMed2000

Is absolute noninvasive temperature measurement by the Pr[MOE-DO3A] complex feasible.

Recently, the feasibility of the praseodymium complex of 10-(2-methoxyethyl)-1,4,7,10-tetraaza-cyclododecane-1,4,7-tr iacetate (Pr[MOE-DO3A]) for non-invasive temperature measurement via 1H spectroscopy has been demonstrated. Particularly the suitability of the complex for non-invasive temperature measurements including in vivo spectroscopy without spatial resolution as well as first spectroscopic imaging measurements at low temporal resolution (> or = 4 min) and high temporal resolution (breath hold, approximately 20 s) has been shown. As of today, calibration curves according to the particular experimental conditions are necessary. This work aims to clarify whether the Pr[MOE-DO3A] probe in conjunction with 1H-NMR spectroscopy allows non-invasive absolute temperature measurements with high accuracy. The measurement results from two different representative media, distilled water and human plasma, show a slight but significant dependence of the calibration curves on the surrounding medium. Calibration curves in water and plasma were derived for the temperature dependence of the chemical shift difference (F) between Pr[MOE-DO3A]'s OCH3 and water with F = -(27.53 +/- 0.04) + (0.125 +/- 0.001) x T and F = -(27.61 +/- 0.02) + (0.129 +/- 0.001) x T, respectively, with F in ppm and T in degrees C. However, the differences are minuscule even for the highest spectral resolution of 0.001 ppm/pt, so that they are indistinguishable under practical conditions. The estimated temperature errors are +/- 0.18 degrees C for water and +/- 0.14 degrees C for plasma and with that only slightly worse than the measurement accuracy of the fiber-optical temperature probe (+/- 0.1 degrees C). It can be concluded that the results obtained indicate the feasibility of the 1H spectroscopy method in conjunction with the Pr[MOE-DO3A] probe for absolute temperature measurements, with a maximum accuracy of +/- 0.2 degrees C.

Agar↗
PubMed2005

Three-dimensional modeling of EXAFS spectral mixtures by combining Monte Carlo simulations and target transformation factor analysis.

We have developed a new method for the three-dimensional modeling of extended X-ray absorption fine structure (EXAFS) spectra which enables the extraction of the local structure of aqueous metal complexes from spectral mixtures of several components. The new method combines two techniques: Monte Carlo simulation and target transformation factor analysis (TFA). Monte Carlo simulation is used to create random arrangements between the X-ray absorbing metal ion and the ligand atoms, and to calculate the theoretical EXAFS spectrum of each arrangement. The theoretical EXAFS spectrum is then introduced as test spectrum in the TFA procedure, to test whether or not the test spectrum is likely to be a component of the spectral mixtures. This coupled procedure is repeated until the error in the test spectrum is minimized. The new method can thus be used to isolate and refine the structure of complexes from spectral mixtures and to determine their relative concentrations, solely on the basis of an estimate of a ligand structure. The performance of the proposed method is validated using uranium Liii-edge EXAFS spectra of binary mixtures of two uranium(VI) 3,4-dihydroxybenzoic acid complexes.

Absorptiometry, Photon↗
PubMed1983

Zonal distribution of cytochrome P-450s (P-450(11) beta and P-450scc) and their relation to steroidogenesis in bovine adrenal cortex.

Zona glomerulosa and zonae fasciculata-reticularis of bovine adrenal cortex were separated by our improved method using a remodeled microtome. A considerable amount of fresh mitochondria and microsomes was quickly obtained. Specific content of cytochrome P-450 in the mitochondria was higher in zonae fasciculata-reticularis than in zona glomerulosa. When metyrapone was added to the mitochondria and the drug-induced difference spectra were measured, there appeared two phases in the titration curve; the first phase was saturated at a concentration of 3 microM and the second phase appeared at concentrations higher than 10 microM. The first phase seemed to be due to the substrate-free P-450(11) beta and the second phase to the cholesterol-bound P-450scc. From these spectral studies contents of cytochrome P-450scc and P-450(11) beta were estimated, and those were found to be equal for each zone. From similar studies on substrate-induced difference spectra, there seemed to be no difference between two zones in the affinity of cytochrome P-450(11) beta for deoxycorticosterone and 11-deoxycortisol. This was also the case with 11 beta-hydroxylase activity and substrate specificity for deoxycorticosterone and 11-deoxycortisol.

Adrenal Cortex↗
PubMed2005

On the age dependency of the macular pigment optical density.

Macular pigment may protect against age related macular degeneration (AMD), because of its capability to absorb blue light and scavenge free radicals. Since age is the major risk factor in AMD, a fundamental question to be answered is the possible age dependence of the macular pigment optical density (MPOD) in normal healthy subjects. In this study we used five methods to study a possible age effect: heterochromatic flickerphotometry, two setups for fundus reflectance spectroscopy, a Scanning Laser Ophthalmoscope (SLO) for obtaining reflectance, and the same SLO for autofluorescence maps. MPOD was determined from the reflected light by a full spectral analysis. We also used a new, directional analysis of the reflected light to estimate MPOD. The latter avoids the disturbing influence of stray-light. Digital subtraction at two wavelengths of log reflectance and digital subtraction of log autofluorescence obtained with the SLO provided MPOD maps. Together, all methods of measuring and of analysis provided seven MPOD estimates per subject. A total of 53 subjects, aged 19-76 years, completed all five measurements (and thus seven analyses). An additional 81 subjects, aged 18-70 years, were measured with one setup for fundus reflectance spectroscopy (and thus only two analyses). We could not find any association with age with all the objective techniques. Only MPOD values obtained with heterochromatic flickerphotometry showed a small, but significant decrease with age. This decrease was caused by an increase in the parafoveal data, suggesting that the central MPOD is unchanged with age. The bivariate correlation coefficients between all methods were significant (all p<0.001).

Adult↗
PubMed2006

Complexation study of cinalukast and montelukast with cyclodextrines.

A fluorimetric study on the spectral characteristics of two antileukotrienes, cinalukast and montelukast, has been performed. Ionization constants of both of them have been photometrically calculated. Cinalukast pK(a) in ethanol:water 50:50 (v/v) medium resulted to be 2.2+/-0.1. Because the spectral characteristics of montelukast are widely affected by the solvent nature, pK(a) was estimated in two different ethanol:water media, 70:30 (v/v) and 10:90 (v/v) and the values calculated were pK(a)=2.9+/-0.1, and pK(a1)=2.0+/-0.1 and pK(a2)=6.5+/-0.1, respectively. It has been proven that the fluorescence of both, cinalukast and montelukast, is significantly intensified in the presence of cyclodextrins (CyDs). The host-guest complexation processes between cinalukast and alpha-CyD or heptakis-(2,6-di-O-methyl)-beta-cyclodextrin (DIMEB) and between montelukast and DIMEB have been investigated by fluorescence spectroscopy. A 1:1 stoichiometric ratio was established for the three studied inclusion complexes. The changes produced on the fluorescence of cinalukast or montelukast, when they are included on the hydrophobic CyD cavity are used to calculate their association constants by a non-linear regression method. Semiempirical MO calculations using AM1 method were performed in order to characterize the studied inclusion complexes. A new method for cinalukast determination in human serum, based on the fluorescence of the complex cinalukast-DIMEB exhibiting limit of detection of 7.95 ng mL(-1) has been proposed with satisfactory results. Adequate recovery values between 95 and 103% were calculated at five different concentration levels.

Acetates↗
PubMed1997

Near infrared light absorption in the human eye media.

Available literature on the spectral transmittance of the eye media in the infrared (IR) is insufficiently accurate to estimate the deposited doses, e.g. in view of light damage risks. Analysis of the data of Boettner and Wolter [Investigative Ophthalmology and Visual Science, 1, 776-783 (1962)] for cornea, anterior chamber, lens and vitreous separately, shows that they can be explained on the basis of the pure water content. The transmittance spectrum of Geeraets et al. [Archives of Ophthalmology, 64, 606-615 (1960)] for all eye media combined is found to be impossible. It is concluded that in the near-IR, light losses in the eye media are best estimated with the absorption coefficient for pure water. A table is given from 700-2500 nm in steps of 10 nm.

Anterior Chamber↗
PubMed2001

A spectrophotometric-partial least squares (PLS-1) method for the simultaneous determination of furosemide and amiloride hydrochloride in pharmaceutical formulations.

A numerical method, based on the use of spectrophotometric data coupled to PLS-1 multivariate calibration, is reported for the simultaneous determination of furosemide and amiloride hydrochloride in synthetic samples and commercial tablets. The method was applied in the concentration ranges of 8.0-13.0 mg l(-1) for furosemide and 1.0-1.6 mg l(-1) for amiloride hydrochloride. Its accuracy and precision were determined, and it was validated by the analysis of synthetic mixtures of both drugs. The method was successfully applied to the quantitation of furosemide and amiloride hydrochloride in three different pharmaceutical formulations, providing results in agreement with those obtained by HPLC. It allowed the rapid, accurate and precise simultaneous estimation of the concentration of both analytes of interest in spite of their important spectral overlap, high concentration relationship and the presence of small amounts of different, unmodelled, absorbing excipients.

Amiloride↗
PubMed1997

Raman spectral evidence for hydration forces between collagen triple helices.

Hydration forces are thought to result from the energetic cost of water rearrangement near macromolecular surfaces. Raman spectra, collected on the same collagen samples on which these forces were measured, reveal a continuous change in water hydrogen-bonding structure as a function of separation between collagen triple helices. The varying spectral parameters track the force-distance curve. The energetic cost of water "restructuring," estimated from the spectra, is consistent with the measured energy of intermolecular interaction. These correlations support the idea that the change in water structure underlies the exponentially varying forces seen in this system at least over the 13-18-A range of interaxial separations.

Collagen↗
PubMed2003

In-vehicle vibration study of child safety seats.

This paper reports experimental measurements of the in-vehicle vibrational behaviour of stage 0&1 child safety seats. Road tests were performed for eight combinations of child, child seat and automobile. Four accelerometers were installed in the vehicles and orientated to measure as closely as possible in the vertical direction; two were attached to the floor and two located at the human interfaces. An SAE pad was placed under the ischial tuberosities of the driver at the seat cushion and a child pad, designed for the purpose of this study, was placed under the child. Four test runs were made over a pave' (cobblestone) surface for the driver's seat and four for the child seat at both 20 km h(-1) and 40 km h(-1). Power spectral densities were determined for all measurement points and acceleration transmissibility functions (ATFs) were estimated from the floor of the vehicle to the human interfaces. The system composed of automobile seat, child seat and child was found to transmit greater vibration than the system composed of automobile seat and driver. The ensemble mean transmissibility in the frequency range from 1 to 60 Hz was found to be 77% for the child seats systems as opposed to 61% for the driver's seats. The acceleration transmissibility for the child seat system was found to be higher than that of the driver's seat at most frequencies above 10 Hz for all eight systems tested. The measured ATFs suggest that the principal whole-body vibration resonance of the children occurred at a mean frequency of 8.5, rather than the 3.5 to 5.0 Hz typically found in the case of seated adults. It can be concluded that current belt-fastened child seats are less effective than the vehicle primary seating systems in attenuating vibrational disturbances. The results also suggest the potential inability of evaluating child comfort by means of existing whole-body vibration standards.

Acceleration↗
PubMed2000

Three-dimensional density spectra of sandy sediments

Power spectra of density variability for sandy sediments offshore Panama City, Florida, are estimated and modeled using digital x-ray computed tomography images of sediment structure. Spectral analysis reveals that while shell pieces and mud mixtures are the main contributors to density variability at large scales, intrinsic density variability associated with sand grain contacts dominates at small scales. The power spectrum of sandy sediments is modeled by an analytic form that consists of two power-law components, one associated with the shell and mud contributions and the other with the intrinsic density variability of sand. The dominant term has a much higher power-law exponent than previously reported. Implications for the scattering of high-frequency sound in sandy sediments are discussed.

Journal Article↗
PubMed1995

Interaction of neuronal populations with delay: effect of frequency mismatch and feedback gain.

The effect of frequency mismatch, signal transduction delay and inter-population feedback gain on the interaction of neuronal populations, mediated by long-range excitation, is investigated using physiologically realistic system parameters. Self-consistent solutions for the frequency, amplitude, and relative phase of the component signals are derived for limit cycle oscillations. These solutions predict important qualitative features including discontinuous changes in frequency of oscillation and phase reversal between symmetric and antisymmetric limit cycles. A singularity in the solutions is used to predict parameter regions in which limit cycles do not exist. If limit cycles exist at zero delay, it is shown that limit cycles and quasi-periodic attractors alternate as a function of delay. The implications of these results for estimating physiologically meaningful delays from observed phase shifts in EEG time series are discussed. Spectral peaks for the quasi-periodic attractor occur at m nu 1 +/- n nu 2, where the difference nu 1 - nu 2 is approximately equal to the intrinsic population frequency mismatch delta nu. The cross-correlation function is amplitude modulated with a frequency equal to delta nu/2, indicating that the two populations slip in and out of phase with a mean correlation duration equal to 1/delta nu. These findings underpin the dynamical basis of delay induced "desynchronization" of oscillations reported in computer simulations. Bifurcation diagrams indicate that quasi-periodic attractors exist for a wide range of parameters in the presence of delay in long-range excitation and non-zero frequency mismatch. If the frequency mismatch is sufficiently large and the feedback gain is sufficiently small, quasi-periodic attractors exist for all delays. Delays of a few milliseconds, much smaller than the system time scale, can destabilize limit cycle oscillations. The role of synaptic change in inducing bifurcations of limit cycles to quasi-periodic attractors and vice versa is discussed. The implication of these findings for the generation of chaos in distributed neural systems is discussed.

Electroencephalography↗
PubMed1987

Properties of proprioceptive neurons in the cuneate nucleus of the cat.

Fifty-two slowly adapting proprioceptive neurons in the cuneate nucleus of chloralose-anesthetized cats were studied. Recordings were made from 3 mm rostral to the obex to 5 mm caudal. The highest densities of proprioceptive neurons were found above and more than 3 mm caudal to the obex. Analysis of the spike trains produced with the forelimb held fixed revealed three basic periodic patterns. Neurons exhibiting these patterns were partitioned into three groups, referred to as the A, B, and C classes. Class A neurons (42%; 22/52) produced regular spike trains that were qualitatively similar to muscle spindle fibers. Interval distributions for this class were typically unimodal and slightly positively skewed. Adjacent intervals were frequently positively correlated. Spectral analysis suggested that 91% of class A spike trains had one to two periodic components. Class B neurons (21%; 11/52) had additional spikes interposed in their periodic discharge; these "interrupting" spikes did not significantly alter the timing of the dominant periodic discharge. Interval distributions were typically bimodal and adjacent intervals were negatively correlated. Spectral analysis suggested that two or more periodic components were present in their spike trains. Class C neurons (36%; 26/52) had spike trains with a basic rhymicity, but when this specific discharge was interrupted, the subsequent interval was near modal length; thus, they were "reset." Interval distributions were usually multimodal and adjacent intervals were frequently negatively correlated. Spectral analysis suggested that C spike trains usually had four or more periodic components. Estimates of information-carrying capacity of each class using a mean rate code and those of primary muscle spindle fibers suggested that a sizable information loss may occur in synaptic transmission. This potential loss was smaller for A-neurons (40%) than for B- (69%) or C-neurons (64%). Electrical stimulation of cutaneous structures influenced 55% (22/52) of the sample. All were members of the B and C classes. Responses were typically biphasic. The cutaneous receptive fields nearly always included a portion of the forepaw. No relationship was found between movement sensitivity and receptive field topography. Contralateral input was found in half (10/20) the neurons tested.

Afferent Pathways↗
PubMed2005

Luminance-color correlation is not used to estimate the color of the illumination.

Humans can identify the colors of objects fairly consistently, despite considerable variations in the spectral composition of the illumination. It has been suggested that the correlation between luminance and color within a scene helps to disentangle the influences of illumination and reflectance, because the surfaces that reflect the light of the illuminant well will normally be bright. Because the reliability of the luminance-color correlation as an indicator of the chromaticity of the illuminant depends on the number of surfaces that are considered, we expected the correlation to be determined across large parts of the scene. To examine whether this is so, we compared different scenes with matched luminance and chromaticity, but in which the correlation between luminance and chromaticity was manipulated locally. Our results confirm that there is a bias in perceived color away from the chromaticity of bright surfaces. However, the results show that only the correlation within about 1 degree of the target is relevant. Thus, it is unlikely that the visual system uses the correlation between luminance and color to explicitly determine the chromaticity of the illuminant. Instead, this correlation is presumably implicitly considered in the way that the color contrast at borders is determined.

Color Perception↗
PubMedDate not supplied

Color Doppler imaging of untreated and irradiated choroidal melanomas.

PURPOSE: We examined untreated and irradiated choroidal melanomas with color Doppler imaging (CDI), a noninvasive method providing quantitative measures of blood flow, to determine if the tumor vessel damage associated with irradiation can be detected using this technology. METHODS: CDI was performed on 122 untreated and 76 previously irradiated tumors using a Q2000 color Doppler ultrasound unit. Spectral analysis was performed on all detectable vascular regions within the tumor to obtain estimates of the peak systolic and end diastolic flow velocities and resistive index ((syst-diast)/syst). RESULTS: Vessels were detected in 93% of the untreated tumors and in 63% of the treated tumors (p<0.001, X2), and the median number of vascular regions found was higher among untreated tumors (3 vs 1, p=0.001, Wilcoxon Rank Sum). The effect of treatment status on the detection of tumor vessels was significant (p=0.039), controlling for age, sex, largest tumor pretreatment diameter, and tumor height at CDI in a logistic regression model. Mean resistive index was lower in the untreated tumors (0.53 vs 0.58, p=0.0050), controlling for tumor height and other covariates in an analysis of variance. CONCLUSIONS: On examination with CDI, irradiated tumors had fewer detectable vascular regions and greater resistance to flow than untreated tumors, a pattern consistent with known radiation effects.

Adolescent↗
PubMed1997

Establishment of ANSI N13.11 X-ray radiation fields for personal dosimetry performance test by computation and experiment.

This paper describes establishment by computational and experimental methods of the American National Standard Institute (ANSI) N13.11 X-ray radiation fields by the Korea Atomic Energy Research Institute (KAERI). These fields were used in the standard irradiations of various personal dosimeters for the personal dosimetry performance test program performed by the Ministry of Science and Technology of Korea in the autumn of 1995. Theoretical X-ray spectra produced from two KAERI X-ray generators were estimated using a modified Kramers' theory with target attenuation and backscatter correction and their spectral distributions experimentally measured by a high-purity germanium semiconductor detector through proper corrections for measured pulse height distributions with photopeak efficiency, Compton fraction, and K-escape fraction. The average energies and conversion coefficients obtained from the computation and experimental methods, when compared with ANSI N13.11 and the recently published National Institute of Standards and Technology X-ray beams, appeared to be in good agreement--(+/-)3% between corresponding values--and thus, could be satisfactorily applied in the performance test of personal dosimeters.

Korea↗
PubMed2003

Surface aerosol radiative forcing derived from collocated ground-based radiometric observations during PRIDE, SAFARI, and ACE-Asia.

An approach is presented to estimate the surface aerosol radiative forcing by use of collocated cloud-screened narrowband spectral and thermal-offset-corrected radiometric observations during the Puerto Rico Dust Experiment 2000, South African Fire Atmosphere Research Initiative (SAFARI) 2000, and Aerosol Characterization Experiment-Asia 2001. We show that aerosol optical depths from the Multiple-Filter Rotating Shadowband Radiometer data match closely with those from the Cimel sunphotometer data for two SAFARI-2000 dates. The observed aerosol radiative forcings were interpreted on the basis of results from the Fu-Liou radiative transfer model, and, in some cases, cross checked with satellite-derived forcing parameters. Values of the aerosol radiative forcing and forcing efficiency, which quantifies the sensitivity of the surface fluxes to the aerosol optical depth, were generated on the basis of a differential technique for all three campaigns, and their scientific significance is discussed.

Journal Article↗
PubMed2005

High-order cumulant-based blind deconvolution of Raman spectra.

The spectra recorded by a dispersion spectrophotometer are usually distorted by the response function of the instrument. To improve the resolving power, double or triple cascade spectrophotometers with narrow slits have been employed, but the total flux of the radiation available decreases accordingly, resulting in a low signal-to-noise ratio and a longer measuring time. The actual spectra can be restored approximately by mathematically removing the effects of the measuring instruments. Based on the Shalvi-Weinstein criterion, a (6, 2)-order normalized cumulant-based blind deconvolution algorithm for Raman spectral data is proposed. The actual spectral data and the unit-impulse response of the measuring instruments can be estimated simultaneously. By conducting experiments on real Raman spectra of some organic compounds, it is shown that this algorithm has a robust performance and fast convergence behavior and can improve the resolving power and correct the relative intensity distortion considerably.

Algorithms↗