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Results for “Radiometry”

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At least 163 records · Page 9Linked to original sources
PubMed1994

[Study of blood sedimentation by photo-thermal radiometry with random excitation].

The erythrocyte sedimentation rate is a complex phenomena involving a large number of parameters. The rate of sedimentation is highly dependent on the haematocrit, the internal viscosity of the red cells and the viscosity of the suspending medium and its composition. The experimental conditions also have a non-negligible effect (geometry and nature of the test tube, temperature, foreign substances in the medium...). In order to respond to the need for more precise and more rapid methods of analyzing the erythrocyte sedimentation rate, we developed new physical methods allowing a real time evaluation of the phenomena involved. Several of these new photothermal methods have already been applied for non-destructive evaluation of thin or layered material (such as composite material or glued structures) both in laboratory situations and in the industry. When a material is placed in a modulated laser beam, the incident rays absorbed heat the sample. The heat then diffuses throughout the material and the surface temperature of the sample increases locally with a periodicity. The surface thus emits a modulated flow of infrared radiation. The amplitude and phase shift of the photothermal signal generated is characteristically dependent of the optic and thermal properties of the material for a given modulation frequency. The early photothermal modelling based on a two-layer model and a physico-mathematical theory of red cell sedimentation proposed by S. Oka made it possible to simulate the phenomena as they occur over time. We hypothesize that the temperature gradients created within the sample are too small to create a convection current and that the all heat transfer occurs by conduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Sedimentation↗
PubMedDate not supplied

[Radiometry of epiphyseolysis capitis femoris. A comparison of conventional roentgen study with axial computerized tomography].

CT scans are proposed for the measurement of tibial, femoral and humeral torsion. The value of computerised tomography in the evaluation of slipped capital epiphysis is yet not discussed. Conventional roentgenographic studies have shown that the capital femoral epiphysis slips by rotating backwards. In a study of 5 cases with a right site slip of the capital femoral epiphysis of different extent a comparison of conventional radiography with CT-scan was undertaken. True lateral films of both hips were obtained at the same time when CT scan of the femoral head and the condylar region of the femur were performed. The optimal site of cross-sectioning the femoral head lies in its center. Both measurements of the epiphysial torsion vary more ore less. This is believed to be related to the different plans in which the upper femoral end is projected in conventional radiography and CT-scan. Both angles of epiphysial torsion are geometrically related. A formula is given for mathematical transfer. Only by marked epiphysial displacement both angles vary to a greater extend. CT scan is suggested to be of certain value in the preoperative evaluation in heavy slips.

Biomechanical Phenomena↗
PubMed1987

A comparison of dosimeters used for solar ultraviolet radiometry.

Radiometric measurements of terrestrial sunlight using three different types of broad-band dosimeters were compared with equivalent integrated quantities obtained from simultaneous spectroradiometric measurements. Measurements were made at Durham, UK (55 degrees N) during one day in mid-summer and one day in the autumn. By this means it was possible to encompass a wide range of ultraviolet irradiances. There was close agreement between UV-A irradiance measured using a broad-band radiometer and determined spectroradiometrically over the whole range of irradiances when allowance was made for the spectral sensitivity of the UV-A radiometer. The agreement between erythemally-effective irradiance determined spectroradiometrically and the response of a Robertson-Berger meter showed some non-linearity due to the mismatch between the erythema action spectrum and spectral response of the sensor. There was a similar disparity in agreement between erythemally-effective dose determined spectroradiometrically and the response of polysulphone film for similar reasons. Nevertheless it is concluded that if these latter two dosimeters are calibrated using sunlight, or a solar simulator, as the source, they can yield data which are sufficiently reliable for many applications.

Radiation Dosage↗
PubMed2003

Infrared 7.6-microm lead-salt diode laser heterodyne radiometry of water vapor in a CH4-air premixed flat flame.

We deal with the design of a diode laser heterodyne radiometer and its application in a combustion process. We present some experimental results obtained with a CH4-air premised flat flame as the optical source. The goal is to prove that heterodyne detection techniques are relevant in remote detection and diagnostics of combustion and can have important applications in both civil and military fields. To the best of our knowledge, it is the first time that this demonstration is made. The radiometer, in spite of the low-power lead-salt diode laser used as a local oscillator, enables us to record high-temperature water-vapor emission spectra in the region of 1315 cm(-1).

Journal Article↗
PubMed2004

Above-water radiometry in shallow coastal waters.

Above- and in-water radiometric data were collected from two coastal platforms: a small boat and an oceanographic tower. The above-water data were processed with and without a correction for bidirectional effects (Q02 and S95, respectively). An intercomparison of water-leaving radiances over a wide range of environmental conditions showed (a) total uncertainties across the blue-green domain were to within 4%, (b) a convergence of the Q02 method with the in-water method (average Q02 intercomparisons were to within 4%), and (c) chlorophyll a concentrations derived from Q02 reflectances and the OC4V4 (Ocean Color 4 Version 4) algorithm agreed with independent high-performance liquid-chromatography determinations to within approximately 32%.

Journal Article↗
PubMed2005

Platform perturbations in above-water radiometry.

A comparison of above- and in-water spectral measurements in coastal (but predominantly Case-1) conditions has shown that the uncertainty in above-water determinations of water-leaving radiances made from an offshore tower depends on the proximity of the above-water measurement with respect to the side of the platform. For purposes of this study the proximity of the sampling platform is parameterized as the perpendicular distance (denoted x) from the side of the sampling platform to the center of the area on the sea surface observed by the sea-viewing sensor, the so-called surface spot, which is set by the field of view of the radiometer (or the overlapping fields of view of a multiaperture sensor). Two above-water data processing methods were used to create a diagnostic variable (formulated for Case-1 waters only but also applicable to Case-2 conditions over short time scales) to quantify the presence of superstructure reflections. Based on the height of the tower, H, the analyses were partitioned into near- and far-field data sets (x < H and x > H, respectively). The primary conclusions of the radiometric intercomparisons are as follows: (a) the maximum perturbations occur very close to the tower ( x/H << 1), and, as x/H increases and approaches 1 (i.e., as the surface spot becomes as far away as the platform is high), the platform perturbations converge toward smaller and smaller values, and (b) within the far field (x > H) the platform perturbation is negligible, and a remote sensing 5% absolute accuracy objective can be satisfied.

Journal Article↗
PubMed2001

Radiometry and wide-angle wave fields III: partial coherence.

The analogs of the generalized radiances introduced in two previous manuscripts [J. Opt. Soc. Am. A 18, 902 (2001) and J. Opt. Soc. Am. A 18, 910 (2001)] for fully coherent fields in two- and three-dimensional free space are given here for the case of partial coherence. These functions are exactly conserved along rays and are suitable for the description of fields with components propagating in any direction. Also defined here is a global measure of coherence, which can be expressed in terms of the new functions. The cases of radiation in a blackbody cavity and partially coherent focused waves are considered as examples.

Journal Article↗
PubMed2004

Diffraction corrections in radiometry: spectral and total power and asymptotic properties.

Wolf's result for integrated flux in the case of diffraction by a circular lens or aperture in the scalar, paraxial Fresnel approximation is considered anew. Compact integral formulas for pertinent infinite sums are derived, and the result's generalizations to extended sources and Planckian sources and asymptotic aspects at small wavelength and high temperature are all considered. Simplification of calculations for an actual absolute radiometer is demonstrated.

Journal Article↗