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At least 73 records · Page 4Linked to original sources

PubMed1990

Reflection confocal laser scanning microscopy of eyespots in flagellated green algae.

The reflection properties of different types of eyespots in three unicellular, flagellated green algae (Tetraselmis chui, Chlamydomonas eugametos, Hafniomonas reticulata) were investigated using confocal laser scanning microscopy in the epireflection mode. The eyespots differed with respect to the number of eyespot lipid globule layers and surface appearance (concave/convex). A strong reflection signal was observed in all eyespots, and a detailed quantitative analysis by optical xy (horizontal) and xz (vertical) sectioning was performed. By applying both sectioning capabilities, multi- and single/double-layered eyespots as well as concave and convex eyespot surfaces could be distinguished using living, immobilized cells. Focusing of the reflected light was only observed in eyespots with concave surfaces. In xz series of multi-layered eyespots at reduced laser intensities (0.01%), the intensity profiles of the reflection revealed a series of alternating maxima and minima with increasing reflection intensities toward the cell surface. At very low laser intensities (0.001%), multi-layered eyespots exhibited about twice the reflection intensity at the presumptive photoreceptor site compared to single/double-layered eyespots. Our results provide the first experimental evidence to support the proposal that multi-layered eyespots act as interference reflectors in photoaxis of green algae.

Chlorophyta↗

PubMed1990

Spectral reflectance of human skin in vivo.

A newly developed skin reflectance spectrophotometer was evaluated for measurements of both melanin pigmentation and erythema. Physiological changes in blood flow and blood content in normal humans were induced by compression with an arm cuff during recording of skin reflectance spectra. Reflectance spectra of UV-induced erythema were also recorded and compared with laser-Doppler flow measurements. Spectral reflectance measurements were found to be highly sensitive in determining minimal erythema, which was not clinically detectable. The measurements of erythema using reflectance spectroscopy and UV irradiation were very highly correlated (r = 0.996). It was possible to calculate the in vivo absorbance of oxygenized haemoglobin. The melanin pigmentation following UV irradiation was quantified by reflectance spectroscopy and correlates highly with the dose of UV irradiation (r = 0.995). Furthermore, regional variations in skin melanin and haemoglobin were analysed for fair Caucasian skin.

Adult↗

PubMed1988

Reflection high resolution analytical electron microscopy: a technique for studying crystal surfaces.

Reflection electron microscopy (REM), reflection high energy electron diffraction (RHEED), reflection electron energy-loss spectroscopy (REELS), and energy dispersion x-ray spectroscopy (EDX) have been comprehensively used as a technique, termed reflection high resolution analytical electron microscopy (RHRAEM), for studying the structures of the bulk crystal GaAs (110) surfaces by transmission electron microscopy (TEM). The simultaneous observations of surface topography imaging, the surface diffraction mechanism with RHEED, surface atomic inner-shell excitations with REELS, and surface chemical compositions with EDX provide a systematic description of the atomic structure and chemical structure of the surface. The surface channelling effect has been observed in GaAs (110) with REELS, which may provide a basis for localizing surface foreign atoms with ALCHEMI. The theoretically predicted surface-resonance wave has been observed directly in the RHEED pattern; the surface-captured Bragg reflection wave have been identified. It is shown that surface chemical compositions can be determined by analyzing the EDX spectra obtained in the REM case. Finally, the surface monolayer resonance characteristic of the RHRAEM has been confirmed by calculations with dynamical RHEED theory.

Arsenic↗

PubMed1989

Reflectance during pulsed holmium laser irradiation of tissue.

Although generally ignored in considerations of laser ablation of tissue, reflectance of laser light from tissue during laser-induced ablation is a potentially important factor in determining ablation efficiency because it determines the amount of laser light coupled into the target. To determine the significance of reflectance changes induced by laser irradiation, we examined the reflectance of liver samples during pulsed holmium laser ablation by placing the target at one focus of an ellipsoidal reflector and a detector at the other focus. The temporal behavior, total reflectance, and effect of multiple pulses were examined. Tissue reflectance as large as 50% was observed during holmium laser irradiation but depended upon laser radiant exposure and number of laser pulses. These measurements suggest that changes in the optical properties of the target during ablation are important and should be considered in detailed modeling of the ablation process.

Animals↗

PubMed1987

Estimation of tissue parameters derived from reflected ultrasound.

We propose a method of estimating two tissue parameters, that is, the reflection coefficient and attenuation coefficient from the reflected ultrasound for the purpose of improving the resolution of ultrasonic images and obtaining information on tissue characterization. The reflection coefficient is estimated by deconvolution technique using Kalman filter taking into account the distortion of the propagating pulse due to the frequency-dependent attenuation. The attenuation is estimated by adaptive processings based upon the criterion function calculated using estimates of the reflection coefficient. Simulated signals are used to investigate the ability of this method. Additionally, actual reflected signals from soft tissues are processed by the method. The results show that the method can be applied in clinical cases.

Animals↗

PubMed1988

Reflection contrast microscopy. Visualization of (peroxidase-generated) diaminobenzidine polymer products and its underlying optical phenomena.

Reflection contrast microscopy (RCM) has proven to be a useful tool for the study of living cells (Ploem 1975). Due to the effective suppression of aspecific reflected light by polarization optics combined with a quarter lambda plate at the front lens of the objective, low intensity reflection signals originating from minor amounts of precipitated diaminobenzidine (DABox) in immunocytochemically stained specimens, can be made visible. RCM has been successfully applied in demonstrating single copy nucleic acid sequences using in situ hybridization procedures (Landegent et al. 1984). We have systematically studied the aspects of image formation of DABox by RCM by using a model system consisting of glass slides coated with peroxidase containing protein layers to determine the conditions for optimal sensitivity of this detection method. Moreover, investigations were performed to study the relationship between the amount of reflected light and DABox depending on the thickness of the object. Both theoretical and practical evidence is obtained to show that DABox detection by RCM is based on interference phenomena occurring in the layer of DABox, and less on selective reflection. This restricts the type of specimen which can be used for sensitive detection of DABox by RCM. Consequently, in ultrathin (40 nm) sections osmificated DABox was visualized in peroxidatic positive cell organelles with high contrast and resolution. Similar results were obtained with immunoperoxidase stained material embedded in Lowicryl under conditions that did not allow visualization of the staining product by bright field microscopy.

3,3'-Diaminobenzidine↗

PubMed1989

Continuous monitoring of gastroduodenal mucosal hemodynamics in rats by laser-Doppler flowmetry and reflectance spectrophotometry.

Gastroduodenal mucosal hemodynamics in rats was monitored continuously by laser-Doppler flowmetry (LDF) and reflectance spectrophotometry, and the validity of these techniques was determined. Corpus mucosal hemodynamics was recorded for 90 min, under stable conditions. In cases of graded hemorrhagic hypotension, corpus mucosal blood flow by LDF and hydrogen gas clearance, and potential differences showed a good correlation. Corpus, antral, and duodenal mucosal hemodynamics monitored by LDF, hydrogen gas clearance, and reflectance spectrophotometry reflected regional hemodynamic differences. In monitoring mucosal hemodynamics by LDF and reflectance spectrophotometry, regular oscillations (4-6 cycles/min) were observed in most animals. The characteristic change of oscillations during graded hemorrhagic hypotension was thus elucidated. In moderate hypotension (50-90 mmHg), high-amplitude and high-frequency (5-10 cycles/min) oscillations were observed, while in cases of severe hypotension (25-40 mmHg), the oscillations almost ceased. Observation of the oscillatory changes is thus a new application of LDF and reflectance spectrophotometry.

Animals↗

PubMed1988

Reflection and transmission of laser light from the esophagus: the influence of incident angle.

The application of lasers in gastrointestinal endoscopy is rapidly expanding. Because of the tubular configuration of the gastrointestinal tract, endoscopists often deliver laser energy at large angles of incidence. As incident angle affects the fraction of radiation reflected from the tissue surface, we measured the transmittance and reflectance of laser light from in vitro esophagus as a function of incident angle, using integrating sphere and goniometric techniques. At a wavelength of 633 nm and angles of incidence less than 50 degrees, the total transmittance of the esophagus is approximately 25% and the total reflectance is approximately 45%; both are isotropically distributed. At larger angles of incidence, a specularly reflected component becomes evident and the total reflectance increases. The absorbed light per unit area illuminated decreases with increasing angle, because the area illuminated by the laser beam is proportional to the secant of the incident angle. The data suggest that during endoscopic laser procedures the incident laser beam should be directed within 50 degrees of normal for optimal performance and safety.

Biophysical Phenomena↗

PubMed1986

Photoplethysmographic evaluation of the relationship between skin reflectance and skin blood volume.

Although photoplethysmography can be used successfully to determine venous recovery time, it cannot be used in tests which rely on a determination of the blood volume change (e.g. maximum venous outflow). In seeking an explanation for this inadequacy it was shown that although the photoplethysmograph is able to indicate changes in reflectance, it is incapable of measuring reflectance, per se; information which is essential for an accurate calculation of venous volume decrease. A minor modification of the system enables relative reflectance measurements to be made. Measurements were performed under in vitro conditions to establish the skin-reflectance/skin-blood volume relationship; photon diffusion theory is then used to describe the skin-reflectance/skin-blood volume relationship and to determine the scattering and absorption coefficients of skin and whole blood.

Blood Volume↗

PubMed1989

Fringe mode reflectance laser Doppler microscope system.

A reflectance fringe mode Laser Doppler microscope anemometer (LDMA) has been designed and tested. A novel beam splitter permits adjustment of the direction and separation of the two laser beams which form the fringe sensing volume, and furnishes the control needed to compensate for chromatic aberration and variation in optical quality. Tests conducted in a narrow 28:1 aspect rectangular flow channel filled with water showed close agreement between the predicted and measured velocity profiles. Velocity measurements, made alternately in the reflectance and transmittance modes using the same sensing volume in the channel, revealed deviations between the modes of less than 1.1% for water and 2.3% for whole blood. The deviation for the in vivo experiment was better than 2.8%. Velocity profiles were measured alternately in the same sensing volume, (dimensions were 10 x 12 microns) by reflectance and transmittance LDMA in 40 hamster cheek-pouch arterioles, ranging from 65 to 140 microns in diameter. These showed close agreement throughout the range of measured vessels. Reflectance LDMA makes non-invasive, high resolution velocity measurements in the range of 0.03 to 40 cm/s possible in small blood vessels near the surface of opaque organs and tissues. The accuracy and reproducibility of the readings were calculated to be better than 1.1%. Reflectance fringe mode LDMA greatly extends the applicability of LDMA because sites where transmittance LDMA can be applied are limited.

Animals↗

PubMed1989

Evoked otoacoustic emissions as cochlear Bragg reflections.

The reflection of cochlear waves is mathematically described for various assumptions about the dependence of the echo-generating mechanism on place and frequency, without requiring knowledge of the physical details of the mechanism. Any 'wave-related' reflections, caused by intrinsic features of the resonance or active-feedback mechanism, cannot explain long group delays in an approximately shift-similar basilar membrane (BM). Only 'BM related' scattering due to inhomogenities is a possible explanation then. Reflection at a fixed point of the BM could cause only narrow-band evoked otoacoustic emissions (EOAEs). Long group delays in a wider frequency band can be obtained by assuming Bragg reflection at an approximately periodic inhomogenity of BM parameters, possibly due to spatial variations of active undamping. This explains the long delays, about inversely proportional to frequency, the decreasing instantaneous frequency, the often found multi-packet or modulated structure of echoes (vanishing at higher SPL), the spectra of simultaneous and delayed EOAEs and their relation to the threshold of hearing. These phenomena do not necessarily require multiple reflection due to middle/inner-ear mismatch.

Auditory Threshold↗

PubMed1991

Quantitative assessment of ultrasonic myocardial reflectivity in hypertrophic cardiomyopathy.

The purpose of this study was to investigate the relation between acoustic properties of the myocardium and magnitude of left ventricular hypertrophy in patients with hypertrophic cardiomyopathy. An on-line radio frequency analysis system was used to obtain quantitative operator-independent measurements of the integrated backscatter signal of the ventricular septum and posterior free wall in 25 patients with hypertrophic cardiomyopathy and 25 normal age-matched control subjects. The integrated values of the radio frequency signal were normalized for the pericardial interface and expressed in percent. Tissue reflectivity was significantly increased in the hypertrophied ventricular septum, as well as in the nonhypertrophied posterior free wall, in patients with hypertrophic cardiomyopathy (58 +/- 15% and 37 +/- 12%, respectively) compared with values in normal subjects (33 +/- 10% and 18 +/- 5%, respectively; p less than 0.001). Furthermore, measurements of reflectivity of the septum or posterior free wall, or both, were beyond 2 SD of normal values in greater than 90% of the patients and were also abnormal in each of the five study patients who had only mild and localized left ventricular hypertrophy. No correlation was identified between myocardial tissue reflectivity and left ventricular wall thickness in the patients with hypertrophic cardiomyopathy (correlation coefficient r = 0.4; p = NS). These findings demonstrate that myocardial reflectivity is abnormal in most patients with hypertrophic cardiomyopathy and is largely independent of the magnitude of left ventricular hypertrophy. Moreover, quantitative analysis of ultrasonic reflectivity can differentiate patients with hypertrophic cardiomyopathy from normal subjects independently of clinical features and conventional echocardiographic measurements.

Adolescent↗

PubMed1987

Critical self-reflection and self-perceived altruism: when self-reward fails.

Social learning theory has produced a three-step model of prosocial development: In the young child, prosocial behavior is elicited by material rewards; in the older child, it is elicited also by social rewards; and in the morally mature adult, it is elicited by self-rewards based on an internalized perception of oneself as a kind, caring, altruistic individual. Self-perception theory has complicated this social learning model by demonstrating that once the third step is reached, the continued presence of material and social rewards may undermine intrinsic prosocial motivation based on self-rewards, producing moral regression. We propose a further complication. Critical self-reflection--the desire to know thyself, warts and all--may introduce a self-deprecating attributional bias that can undermine self-perceived altruism, even following helping for which one receives only intrinsic self-rewards. Two experiments are reported in which we manipulated critical self-reflection on one's reasons for helping. Results indicated that self-reflection undermined self-perceived altruism, especially when the salience of the self-rewards for helping was high. Experiment 2 also provided evidence that, as predicted, this self-reflection effect was most apparent for individuals who valued self-knowledge more highly than concern for others. Moral consequences of critical self-reflection are discussed.

Altruism↗

PubMed1985

Reflection of CO2 laser radiation from typical surfaces encountered in hospital environments.

Measurements of the reflectivity of CO2 laser radiation (10.6 micron) from typical clinical surfaces are reported. The results obtained confirm that stray reflections from these surfaces could be a potential hazard to both patient and hospital staff. Some conducting surfaces, for example, reflect up to 95% of the radiation incident upon them and even dielectrics reflect over 50% in some cases. The results reported are for linearly polarised light only. Strong evidence is shown that the deposition of certain thin coatings dramatically reduces the percentage of 10.6 micron radiation reflected.

Carbon Dioxide↗

PubMed1986

Dream self-reflectiveness as a learned cognitive skill.

This research was directed toward the contradiction sustained by cognitive dream psychology, which on the one hand regards dreaming as higher symbolic activity and, on the other, sees its organizational and functional characteristics as derivative and/or inferior to those of waking consciousness. Study 1 evaluates the degree of self-reflective meta-cognition in dreams from different sleep stages. Subjects were 24 college students selected such that half were self-reported high-frequency dream recallers and half were low-frequency recallers. Both groups were composed equally of men and women. Greater self-reflectiveness (SR) was found in REM dreams as compared with those from stages 2 and 4, which did not differ. High-frequency recallers showed more dream SR than did low-frequency recallers. Study 2 assessed the extent to which self-reflective and lucid dreaming can be learned as a cognitive skill by varying levels of intention and attention paid to dreaming. After 3 weeks of home dream collection, results showed that four experimental groups had greater dream SR than did a baseline group. The most effective treatment was the mnemonic, wherein attention patterning schemas learned in waking resulted in more self-reflective and lucid dreaming than did either baseline or attention-control conditions. These results provide evidence that dreaming is not single-minded but variable along a self-reflective process continuum, and suggest functional and organizational levels that are consistent with the conception of dreaming as higher order cognitive activity.

Adult↗

PubMed1986

Capillary permeability in rat hindquarters as determined by estimations of capillary reflection coefficients.

Osmotic reflection coefficients (sigma) for a variety of solutes ranging from NaCl to albumin were determined in perfused maximally vasodilated rat hindquarters employing the osmotic transient method (Vargas & Johnson 1964). Measurements were performed at high flows and using short tubings with small volumes. Intracapillary solute concentrations of the osmotic transients were measured or estimated for solutes of the size of inulin or smaller. The PS for Cr-EDTA and cyanocobalamine were determined repeatedly in half of the experiments using an on-line modification of the single injection (indicator diffusion) method (Rippe & Stage 1978) and capillary filtration coefficients (CFC or LpS) were followed in all experiments. The capillary osmotic reflection coefficient was determined to 0.05 for NaCl, to 0.08 for sucrose, to 0.39 for inulin, to 0.57 for myoglobin and to 0.87 for albumin. These reflection coefficients were compatible with a 'small pore radius' of approximately 40 A (slit width (w) of approximately 50 A) according to modern hydrodynamic theories for the reflection coefficient and the parallel transcapillary pathway hypothesis. The best fit of the osmotic transient data to current theories for the reflection coefficient occurred if the major portion (86-87%) of the hydraulic conductivity (Lp) was accounted for by this paracellular 'small pore' (slit) pathway and if 3.0-4.1% of Lp could be ascribed to a transcellular pathway (sigma approximately I) while the remaining fraction (10%) of Lp was accounted for by a non-selective paracellular pathway (sigma approximately o); that is, by 'large pores'.

Animals↗

PubMed1989

The left paratracheal reflection.

The left paratracheal reflection, which is found medial to the left subclavian artery reflection, was sought in 302 normal posteroanterior (PA) chest radiographs, 93 conventional chest tomograms, and 113 thoracic computed tomographic (CT) scans. The left paratracheal reflection was visible on 31% of normal PA chest radiographs. Conventional tomography and CT showed that this finding is produced by contact of the lung with the mediastinum anterior to the left subclavian artery. The CT scans studied showed that the left paratracheal reflection actually represents contact of the lung with left paratracheal mediastinal fat 94% of the time, with the proximal 1-2 cm of the lateral wall of the left common carotid artery 5% of the time, and with the left tracheal wall 1% of the time. A variety of entities may alter the left paratracheal reflection.

Adult↗

PubMed1979

Propagation velocity and reflection of pressure waves in the canine coronary artery.

In this study the pressure wave velocity in the anterior descending branch of the left coronary artery (LADC) of the dog was measured by determining the delay time between pressure pulses along this artery. This method can only be applied if reflections of the pressure wave distal to the sites of pressure measurement are insignificant. From araldite casts of the coronary arteries the following relation between the diameter proximal to (dprox) and distal to (ddist 1, ddist 2) a bifurcation was found: dprox2.55 = ddist12.55 + ddist 22.55, indicating that reflections at a bifurcation areminimal. In dogs reflections were studied by inducing during diastole a pressure pulse in the aorta and measuring pressure and volume flow proximal to and pressure distal to a segment of the LADC at various levels of the coronary peripheral resistance. Reflection of high-frequency components (greater than 7 Hz) was found to be insignificant, allowing application of the above-mentioned method for measuring the wave-front velocity, which is insensitive to low-frequency reflection. At a pressure in the LADC of 13.3 kPa this velocity was 8.6 +/- 1.4 m.s-1 (mean +/- SD). The calculated dynamic cross-sectional stiffness (deltaP/(deltaA/A)) of the LADC was 97 +/- 11 kPa (mean +/- SE) at an arterial pressure of 13.3 kPa.

Animals↗