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At least 1,351 records · Page 75Linked to original sources
PubMed2000

Twenty-four hour urinary sodium and 3-methylhistidine excretion in relation to blood pressure in Chinese: results from the China-Japan cooperative research for the WHO-CARDIAC Study.

We examined the associations between sodium and blood pressure (BP), and between 3-methylhistidine (3MH) (a marker of animal protein intake) and BP in four Chinese population samples (Guiyang, Guangzhou, Shanghai and Shijiazhuang). This work was a constituent part of the World Health Organization (WHO) Cardiovascular Disease and Alimentary Comparison (CARDIAC) Study. Each population sample consisted of 100 men and 100 women aged 48-56 yr and randomly selected using a cross-sectional study design. Twenty-four hour urine samples were collected. Urinary sodium and potassium excretion levels were measured by the flame photometry method, and 3MH was measured using a Hitachi Amino Acid Analyzer 835 (Hitachi, Ibaraki, Japan). After excluding subjects who did not complete the 24-h urine collection (as assessed by urinary creatinine excretion in relation to weight), the total study group included 314 men and 355 women. The results showed that (1) Sodium was positively, and 3MH negatively associated with systolic and diastolic BP (SBP, DBP) in both the total sample and in those who were not administered anti-hypertensive drugs; these associations were all significant (p< 0.05), and remained so after adjustment for age, sex, body mass index [BMI, weight (kg)/height (m2)], alcohol intake and potassium excretion. Sodium and 3MH were also observed to exert a combined effect on BPs. In general, subjects who had higher sodium and lower 3MH levels had higher mean SBP and DBP. This combined effect was particularly clear on SBP. (3) A positive association between sodium and BP, and a negative association between 3MH and BP were also shown in subjects who had BMI less than 26 kg/m2. In conclusion, the study confirmed and further extended previous observations on the study of salt and animal protein intake in relation to BP in middle-aged Chinese. The results support recommendations for a reduction in high salt intake for the control of high BP in the general population and in those with lower BMI. The results also provide important evidence that adequate animal protein intake may have a favorable effect on BP.

Aging↗
PubMed2002

Mathematical formulations for the schlieren detection method applied to the measurement of photodeformation.

In a schlieren detection scheme for photodeformation measurements, the divergence of the probe beam that is induced by the axisymmetric but radially inhomogeneous periodic photothermal displacement of the surface of a sample is transformed into an intensity variation by insertion of an iris in front of the detection photodiode. We present three expressions for the intensity profile of a Gaussian laser beam that is reflected by the inhomogeneous photodeformation of a solid. The first expression proceeds from geometrical optics (or photometry), whereas the second one derives from the use of the well-known ABCD law and the third one from diffraction principles. Comparing these formulations of the schlieren signal with their behavior as a function of different geometrical parameters, we obtain the domain of validity of each expression, and we deduce the advantages of the different formalisms.

Journal Article↗
PubMed2002

Matrix description of coherent and incoherent light reflection and transmission by anisotropic multilayer structures.

We propose a matrix method for the description of light reflection and transmission by an anisotropic multilayer system consisting of thin and thick layers. A method based on partial-wave matrix summations is applicable in the field of reflection and transmission photometry and ellipsometry. In the case of a thin anisotropic film, the interference effects were described by use of a coherent summation of Jones matrices. Incoherent intensity summations for a thick weakly anisotropic layer were characterized by use of the coherency vector formalism. Observable quantities or Mueller matrix components were obtained from the matrix describing transformation of the coherence vectors.

Journal Article↗
PubMed2003

Halo polarization profiles and sampled ice crystals: observations and interpretation.

Simultaneous two-wavelength polarization and radiance distributions have been obtained for 22 degrees parhelia in four Antarctic ice-crystal swarms that extended to ground level. Samples of crystals that produced these parhelia were collected and replicated. The wavelength dependence of the width of the halo polarization peak agrees with Fraunhofer diffraction theory, indicating that the broadening of the halos is caused primarily by diffraction. However, the observed broadening is much more than predicted from the size distribution of the replicated crystals. From one halo display to the other, the ratio of observed/predicted broadening is erratic, suggesting size-dependent collection efficiency in the sampling. This would imply that, for South Pole conditions, halo polarimetry (or even photometry) is a more reliable method for crystal size determination than actual sampling. It also implies that shapes of the sampled crystals need not necessarily be representative for the shapes of the halo-making crystals in the swarm. Our previous hypothesis [Appl. Opt. 33,4569 (1994)], that a spread of interfacial angles is the dominating cause of halo broadening, has proved untenable.

Journal Article↗
PubMed2004

High-resolution photometric optical monitoring for thin-film deposition.

Real-time monitoring of thin-film deposition with high resolution is important for precise fabrication of thin-film devices in a technological environment with ever-increasing demands for smaller size and better performance. Using photometry, we were able to achieve a real-time optical monitoring resolution of film thickness that is comparable with a single atomic layer scale (i.e., subnanometer). Filtering noise efficiently and compensating for sources of error by use of an appropriate model produced this high resolution. The procedure proved reliable and can be useful in the thin-film-deposition industry.

Journal Article↗
PubMed2005

Reevaluation of the quondam dust trend in the middle atmosphere.

Quondam lunar eclipse photometry data offered valuable information on the optical properties of the middle atmosphere, including dust particles. However, in comparison with nonspherical grains, the simple model of spherical particles has a different effect on solar radiation penetrating horizontally through the atmosphere. It is shown that the systems, in which the smallest size fraction of dust particles dominates, reduce irradiation of the Earth's shadow more efficiently if the grains are of irregular shape. In contrast, the populations contaminated by a certain amount of large particles cause an opposite effect. Depending on the actual form of the size distribution function of the irregular grains, the irradiance within the center of the Earth's shadow may change by 2 orders of magnitude in the visible spectrum. It is therefore evident that dust properties retrieved in the past are eligible candidates for reevaluation to correct a view on the dust trend in the middle atmosphere. Sample calculations are presented for the lunar eclipse observed on 19 January 1954.

Journal Article↗
PubMed2005

Determination of optical parameters of a twisted-nematic liquid crystal by phase-sensitive optical heterodyne interferometric ellipsometry.

What is believed to be a novel phase-sensitive optical heterodyne interferometric ellipsometer is set up to characterize a twisted-nematic liquid crystal (TN-LC) by the elliptical parameters of the output polarization state. This ellipsometer presents the advantages of both polarized optical heterodyne interferometry and optical photometry, which introduce a polarization modulation that is capable of performing with high-sensitivity on phase detection in real time. The twist angle phi and the untwisted phase retardation gamma of TN-LC are measured precisely. The experimental results verify that a TN-LC can be treated as identical to an elliptical retarder.

Journal Article↗
PubMed2006

Simple spectral stray light correction method for array spectroradiometers.

A simple, practical method has been developed to correct a spectroradiometer's response for measurement errors arising from the instrument's spectral stray light. By characterizing the instrument's response to a set of monochromatic laser sources that cover the instrument's spectral range, one obtains a spectral stray light signal distribution matrix that quantifies the magnitude of the spectral stray light signal within the instrument. By use of these data, a spectral stray light correction matrix is derived and the instrument's response can be corrected with a simple matrix multiplication. The method has been implemented and validated with a commercial CCD-array spectrograph. Spectral stray light errors after the correction was applied were reduced by 1-2 orders of magnitude to a level of approximately 10(-5) for a broadband source measurement, equivalent to less than one count of the 15-bit-resolution instrument. This method is fast enough to be integrated into an instrument's software to perform real-time corrections with minimal effect on acquisition speed. Using instruments that have been corrected for spectral stray light, we expect significant reductions in overall measurement uncertainties in many applications in which spectrometers are commonly used, including radiometry, colorimetry, photometry, and biotechnology.

Journal Article↗
PubMed2006

Light backscatter by surfaces composed of small spherical particles.

We present measurements of phase angle curves of intensity and degree of linear polarization of powdery surfaces at two spectral bands centered near 0.44 and 0.63 microm. Three powder samples consisting of nonabsorbing spherical particles of sizes comparable with the wavelengths 0.5, 1.0, and 1.5 microm were examined. The particulate surfaces were measured in the phase angle range of 0.2 degrees-50 degrees by two different photometers and/or polarimeters. At small phase angles, powdery samples consisting of spherical particles (having very high albedo that resulted in significant multiple scattering) showed prominent features that corresponded to single-particle scattering. These features became more prominent after compressing the surfaces when we changed the packing density of the powders from 0.29 to 0.48. Noticeable differences were observed between polarimetric curves corresponding to different wavelengths. All the samples demonstrated prominent opposition intensity spikes at phase angles <2 degrees likely caused by the coherent backscatter enhancement due to multiple scattering within the particulate surface. The intensity phase curves at these two wavelengths were similar. The photopolarimetric measurements may have broad applications to the interpretation of photometry, spectroscopy, and polarimetry of the ice regoliths of high albedo satellites.

Journal Article↗
PubMed2006

Influence of multiple reflections on transmission through a stack of plates.

We examine the problem of light transmission along the normal through a stack of flat plates whose thicknesses and separations vary. For a modest number of plates, an exact calculation is straightforward, but then one must address how to average over both the disorder in the stack and the distribution of incident wavelengths. Model calculations are used to show that an average over the light's distribution can suppress most of the fluctuations due to disorder. Our results are in qualitative agreement with experimental data and imply that multiple reflections do contribute significantly to the measurements. Finally we explore the effect of multiple reflections on photometry.

Journal Article↗
PubMed1977

Color vision in the peripheral retina. I. Spectral sensitivity.

Spectral sensitivity was measured by heterochromatic flicker photometry both in the fovea and at 45 degrees in the periphery, using a 1200 troland standard. At each location, sensitivity functions were obtained using both large and small targets. While the foveal functions were normal, the peripheral ones showed a large enhancement in sensitivity to short wavelengths relative to long wavelengths. Similar results in the past had been criticized on the ground that they might have been due to differential chromatic adaptation of cone mechanisms. In this study such an interpretation was ruled out by additional control experiments including varying luminance and wavelength of the standard light. The possibility of a rod contribution to the peripheral functions could not be eliminated although several different techniques, including the Stiles-Crawford effect, were used to try to isolate cone mechanisms.

Adult↗
PubMed1977

Chromatic two-pulse resolution with and without luminance transients.

Two-pulse discrimination thresholds determined for homochromatic pulses presented as luminance increments or decrements are invariant with wavelength. Wavelength does affect two-pulse temporal resolution if chromatic pulses are presented in hue substitution, matched in luminance (with flicker photometry) to an achromatic background field. For relatively long pulses, the wavelength effect resembles trichromatic saturation discrimination, with poorest temporal resolution at 570 nm. For shorter pulses, temporal resolution for hue substitution stimuli appears related to saturation discrimination under conditions of artificial tritanopia. Under conditions of hue substitution, short-wavelength pulses yield good temporal resolution.

Color↗
PubMed1979

Duration thresholds for chromatic stimuli.

The duration necessary to detect chromatic stimuli was measured for wavelengths between 463 and 620 nm. Stimuli were presented either in hue substitution (replacement of white by a chromatic stimulus of matched luminance) or as increments. Two observers viewed a 1 degrees 45' homogeneous white field. A trial consisted of replacement of the central 40' of the field by a chromatic stimulus. In substitution mode the white field was 2.4 cd/m2., the chromatic replacement was of matched luminance using heterochromatic flicker photometry (HFP). In increment mode, the white field was decreased to 1.2 cd/m2., the chromatic replacement remained at 2.4 cd/m2. In substitution mode, duration threshold varied from approximately 3--4 ms for the spectral extremes to 45--66 ms at 570 nm. Detected stimuli were always seen as a change in chromaticity. In increment mode, thresholds were in the 2--4 ms range with no dependence upon spectral composition. Detected stimuli were seen either as changes in chromaticity or brightness. A control experiment indicated that HFP did establish equivalent luminance for the hue substitution mode. We conclude that duration thresholds in substitution mode reveal chromatic processing channels; duration thresholds in increment mode are mediated by chromatic and/or achromatic processing channels.

Color Perception↗
PubMed1980

Vector model for normal and dichromatic color vision.

The inclusion of cone mechanisms in a slightly revised version of an earlier model allows accounts of phenomena that involve receptor effects as well as dichromatic color vision. Intensity-dependent parameters that stimulate the adaptation of receptors and opponent and nonopponent mechanisms are varied to predict a wide range of data for both normals and dichromats, including: (i) color matching; (ii) the approximate apparent hue and saturation of the spectrum; (iii) foveal spectral sensitivities obtained by flicker photometry and by detection in the dark and under conditions of achromatic or chromatic adaptation; (iv) heterochromatic additivity failures in the dark-adapted and chromatically adapted eye; (v) approximate differences between brightness and luminance; and, (vi) color and wavelength discrimination under varying adaptation conditions.

Color↗
PubMed1980

Spectral sensitivity in the far peripheral retina.

Relative spectral sensitivity was measured at different intensity levels 45 degrees temporally during the cone-plateau period and in a dark-adapted state. Both heterochromatic brightness matching, flicker photometry, and threshold measurements were employed. The relative spectral sensitivity obtained during the cone-plateau period was found to coincide closely with the foveal luminosity function in the long and medium regions of the spectrum irrespective of intensity and method employed, suggesting that the relative spectral sensitivities and the weighted contributions of the long- and medium-wavelength cone photopigments do not change appreciably between fovea and 45 degrees. The relative spectral sensitivity obtained in the dark-adapted state, on the other hand, was found to be purely scotopic in form invariant to intensity and method, suggesting that it is dominated almost completely by rod activity even at intensity levels commonly labeled "photopic.

Dark Adaptation↗
PubMed1982

Brightness of equal-luminance lights.

The brightness of lights defined by heterochromatic flicker photometry as being of equal luminance was determined by direct comparison with a white standard. Stimuli included mixtures of white and colored lights. Eight different colorimetric purities were tested for each of eleven primaries. Adaptation to a known white was maintained. Resulting brightnesses were expressed in terms of the ratio of the amount of light required for a brightness match to the amount required for a flicker photometric match (B:F). B:F ratios varied with the primary, being largest for red and blue primaries. The variation of B:F ratio with colorimetric purity differed depending on the primary, although for any given dominant wavelength the highest-purity stimulus always had the largest B:F ratio. The data qualitatively exclude a number of simple models of brightness generation.

Color↗
PubMed1983

Phase shift in red and green counterphase flicker at high frequencies.

When balanced red and green lights are alternated more than 20 times per second, the perceived flicker can be reduced by advancing the green flicker about 10 degrees of the red-green cycle. The required advance for least flicker is greatest at retinal illuminances around 1000 td and frequencies between 30 and 35 Hz. A model that predicts tuning at this frequency exists, but the tuning curve that is predicted is broader than that observed. A modified model is left for future publication. Meanwhile, other empirical properties of the advance required by green over red are described. In addition to the intensity dependence of this phase shift, we describe its dependence on intensity balance between red and green. Also, the intensity balance turns out to depend on the frequency being used, in contrast to the independence expected by Ives, the inventor of heterochromatic flicker photometry.

Color Perception↗
PubMed1993

Motion at isoluminance: motion dead zones in three-dimensional color space.

Under some conditions, moving isoluminant stimuli perceptually slow down or even appear to stop. The purpose of the experiment was to explore the shape of the motion dead zone, the region of color space over which the perception of stopped motion occurs. Subjects viewed a small patch of moving grating (2.3 deg x 2.3 deg, 1.3 cycles/degree, 2.9 deg/s), that was spatially modulated in chromaticity, luminance, or both, presented either foveally or at 2-deg eccentricity. The bars of the grating moved from both edges inward toward the center of the patch. Subjects set perceptual motion boundaries by adjusting the contrast of the luminance-modulation component of the grating. Over most or all of the available gamut of chromatic contrasts, the upper and lower boundaries of the motion dead zone formed two parallel planes near the V lambda-isoluminant plane in three-dimensional color space. The data thus suggest that under the conditions of the experiment, perceptual-motion boundaries are determined largely or entirely by the luminance contrast of the stimulus. The data also provide the most extensive evidence available to date for the additivity of motion photometry.

Adult↗