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PubMed1989

Laser reflections from relatively flat specular surfaces.

A major element in laser range control procedures has been the control of stray reflections from glass reflectors which may be near the laser target. These hazardous reflections have been thought to extend as far as the direct beam for near grazing angles of incidence. Modern military laser rangefinders and designators can be hazardous to the unaided eye to distances of 10 km or even greater. For this reason, many square kilometers of laser range area have been necessary to conduct laser tests when flat specular reflectors may be present on targets. Fortunately, sophisticated pointing systems have been developed with these laser systems to ensure that the direct beam is confined to the immediate target area. In most cases, flat specular reflectors also have been eliminated from the immediate target area. In some instances, however, specular reflectors still exist near or on laser targets. For these special cases, a more definitive mathematical treatment of hazardous laser reflections is desired. The divergence of a laser beam which has been reflected from a flat specular surface is dependent on the size of the reflector, the divergence of the laser creating the reflection, and the curvature of the reflecting surface. It can be shown mathematically that the curvature of even an optical flat, a reference surface used to compare the flatness of other surfaces, will produce a significant additional beam spread, thereby reducing the hazards of reflected beams. The natural curvature of plate glass or window glass is much greater, reducing the hazards even further. The extent of the hazards for reflections of various types of lasers and reflecting surfaces is discussed.

Eye Injuries↗

PubMed1998

Use of image-based information in judgments of surface-reflectance properties.

We examined how well we can recover surface-reflectance properties from shading patterns under changes in surface shape. The stimulus we used was a square surface modulated in depth by a low-pass-filtered random field and rendered by the Phong illumination model [Commun. ACM 18, 311 (1975)]. Two different surface images (target and match) were presented side by side, with either the viewing direction or the surface-normal direction rotating around the horizontal axis. The target shape was manipulated by changing the spatial spectrum, and the target reflectance was manipulated by changing the diffuse-reflection coefficient and the specular-reflection exponent (shininess) of the Phong model. The shape parameters of the match stimulus were fixed, but its reflectance parameters were under the control of subjects, who had to make the apparent reflectance of the two surfaces as similar as possible. The results showed that the constant error (difference between simulated and matched values) was large except when the two surfaces had the same shape parameters or when they differed only in scale. The pattern of the constant errors and response variabilities suggests that the judgments of the subjects were based on the similarity of the luminance histogram of the surface image. Our results demonstrate a limitation of surface-reflectance constancy for changes in shape and the importance of image-based information in reflectance judgments. The results are discussed in relation to previous studies that showed effects of spatial layout on surface-reflectance perception.

Color Perception↗

PubMed1986

Evaluation of linear models of surface spectral reflectance with small numbers of parameters.

Recent computational models of color vision demonstrate that it is possible to achieve exact color constancy over a limited range of lights and surfaces described by linear models. The success of these computational models hinges on whether any sizable range of surface spectral reflectances can be described by a linear model with about three parameters. In the first part of this paper, I analyze two large sets of empirical surface spectral reflectances and examine three conjectures concerning constraints on surface reflectance: that empirical surface reflectances fall within a linear model with a small number of parameters, that empirical surface reflectances fall within a linear model composed of band-limited functions with a small number of parameters, and that the shape of the spectral-sensitivity curves of human vision enhance the fit between empirical surface reflectances and a linear model. I conclude that the first and second conjectures hold for the two sets of spectral reflectances analyzed but that the number of parameters required to model the spectral reflectances is five to seven, not three. A reanalysis of the empirical data that takes human visual sensitivity into account gives more promising results. The linear models derived provide excellent fits to the data with as few as three or four parameters, confirming the third conjecture. The results suggest that constraints on possible surface-reflectance functions and the "filtering" properties of the shapes of the spectral-sensitivity curves of photoreceptors can both contribute to color constancy. In the last part of the paper I derive the relation between the number of photoreceptor classes present in vision and the "filtering" properties of each class. The results of this analysis reverse a conclusion reached by Barlow: the "filtering" properties of human photoreceptors are consistent with a trichromatic visual system that is color constant.

Analysis of Variance↗

PubMed1989

The spectral reflectance of the nerve fiber layer of the macaque retina.

This paper reports the first quantitative measurements of the reflectance spectrum of the nerve fiber layer (NFL) of the retina. An arcuate defect in the NFL of two macaque monkeys was produced by photocoagulating a small spot near the optic disc. Imaging fundus reflectometry at 8 wavelengths was then used to measure the fundal reflectances in the defect and in the intact NFL. The reflectance of the NFL alone was determined by subtracting the reflectance of the bare fundus in the defect from the reflectance of the adjoining fundus with intact NFL. The reflectance data were corrected for the transmission of the ocular media with published values of the density of monkey cornea and lens. Lens absorption was measured from Purkinje images and differed little from the published values. The NFL reflectance can be characterized by a spectrum that has the same shape at all points along an arcuate region of the NFL but decreases in absolute reflectance as the thickness of the NFL decreases. The reflectance changes little between 680 and 560 nm, but rises as lambda-n from 560 to 460 nm, where n = 2.5-3.1. The data reported here begin to provide a quantitative understanding of empirically determined methods for enhancing the visibility of the NFL and have implications for retinal densitometry.

Animals↗

PubMed1981

Evaluation of reflection interference contrast microscope images of living cells.

Reflection contrast microscope methods are generally used for studies of those portions of the cell that are turned towards the glass coverslip, to comprehend the structure of the cytoskeleton and the dynamics of cell movement, as well as formation of cell-glass contacts. In incident illumination only reflected light contributes to picture formation. The intensity of which in the case of observation of unstained cells is small because of small refraction differences. To overcome this problem a reflection contrast system was developed by Leitz according to Ploem [49], in which by using contrast preserving measures the reflection becomes prominent in comparison with the lens reflexes. The emerging pictures are a result of interferences of reflections at glass-cell, cell-culture medium and culture medium-cell interfaces. According to Fresnel's equations the reflected intensity depends on the differences of the particular refractive indices and the thickness of the layers, which determine the phase of interfering beams. In idealized systems of thin films the reflected intensity is a measure for their optical constants. Relative reflection measurements from glass-cell areas is comparison with the known glass-medium reflection, can therefore be revealing as far as refraction index, cell-glass distance or cell thickness are concerned. The estimates by Bereiter-Hahn et al. [15] were made in the assumption of vertical illumination neglecting its actual conical shape: the comparison of two Fresnel functions of cytological relevant measurements show - in accordance with Gingell and Todd [24] - that this is only permitted under certain conditions, depending on the required accuracy of the measurements; an incidence angle of about 30 degrees leads to an error of about 10%, an angle of 50 degrees to more than 50%.

Animals↗

PubMed1998

Incorporating the service accomplishments into pre-registration curriculum to enhance reflective practice.

Much emphasis is being placed on the importance of reflective practice as a means to ensure that practitioners are competent in their practice. It is therefore important to ensure that student nurses acquire these reflective skills as part of their development throughout pre-registration curricula. Although reflective practice is seen as a major part of curricula activity, the style in which reflection is advocated takes many different formats. Strategies for developing reflection which focus on outcomes for students can become subjective and fail to place healthcare practice within the context of social structures and values. This paper offers a framework for reflection that promotes an outlook which is both objective and subjective, based on Mezirow's six levels of reflection (as adapted by Powell 1989) and O'Brien's (1987) five service accomplishments. Focus of reflection within the wider context of society and healthcare policy should enable development of a practitioner who is both competent in practice and can analyse and evaluate their practice.

Aged↗

PubMed1998

The role of nurse educators in the development of reflective practitioners: a selective case study of the Australian and UK experience.

The potential to improve patient/client care, stimulate the personal and professional growth of the practitioner and help close the theory practice gap has provoked much discussion in the nursing literature on the benefits of reflection on practice. In order to examine recent developments in this area, a study tour, supported by the Florence Nightingale Foundation, was conducted in Australia and the UK during the spring and summer of 1995. Using an illuminative case study approach, data collected demonstrated that although reflective practice was fully endorsed by the nursing profession in Australia, and there were excellent examples of reflective practice in use, the continued growth of the reflective practice movement appeared to be threatened by the rationalization of both clinical and theoretical education in the universities. Issues around methods of encouraging reflection in students focused on ethical use of journals, the levels of reflection developed and the outcome effectiveness of reflective learning. Although it is recommended that the nursing profession continue to endorse developments in reflective practice in the UK, it is also necessary to encourage both process and outcome evaluations of its effects on the development of the individual nurse and on the ensuing quality of health care delivery.

Australia↗

PubMed2001

Low-reflection-coefficient liquid interfaces for system characterization.

The use of liquid brominated hydrocarbons to form a planar reflecting interface with water is described. Gravity-based planar reflecting surfaces with known reflection coefficients can be used in system characterization for quantitative ultrasonics, and a set of surfaces with a range of reflection coefficients allows calibration of the output power and receiver gain of ultrasonic imaging systems. The substances reported here are immiscible in water and form interfaces with water, resulting in a broad range of acoustic reflection coefficients. Reflection coefficients were measured at temperatures from 18-24 degrees C for "pure" substances and for mixtures of two brominated hydrocarbons. Results show that reflection coefficients are weakly dependent on temperature and that, at a specific temperature, a significant range of arbitrarily small reflection coefficients is available, in the case of the mixtures, by the appropriate choice of weight-percents of the two brominated hydrocarbons.

Hydrocarbons, Brominated↗

PubMed2002

Appraising and assessing reflection in students' writing on a structured worksheet.

BACKGROUND: A variety of teaching and learning techniques intended to engage students in reflection are either in use or are being developed in medical and dental education. In line with evidence-based practice in education, research is needed to appraise the utility and effectiveness of these techniques, so that they may be used with confidence. AIM: To assess whether students completing a 'reflective' learning activity based on a structured worksheet really were reflecting. METHOD: A qualitative, multi-method approach was taken. Worksheets completed by students were examined for evidence of reflection by researchers using two sets of criteria for the assessment of reflection derived from the literature, and by peer judges using their own criteria. The opinions of students completing the activity, regarding its acceptability and utility, were elicited by a questionnaire incorporating a 5-point Likert scale. RESULTS: Results from all methods suggest that students completing the activity were reflecting. Students' opinions of the activity were mainly positive. CONCLUSION: The methods employed may be of use to educators wishing to appraise reflective learning activities or, possibly, to assess student reflection.

Clinical Competence↗

PubMed1976

Reflection in the systemic arterial system: effects of aortic and carotid occlusion.

Experiments were performed in seven closed-chest anaesthetized male dogs to determine the role of pulse wave reflection in the pattern of flow and pressure in the ascending aorta. Ten days after implantation of an electromagnetic flow transducer around the ascending aorta a balloon catheter was placed in the descending aorta via the femoral arteries. At the same time a tip manometer was introduced into the ascending aorta. Aortic occlusions at three different sites caused pressure pulses with secondary systolic rises and flow pulses with biphasic deceleration. Secondary rises occurred 45 +/- 9.0 ms after the initial pressure rise for high aortic occlusion; this time was 75 +/- 8.5 ms for occlusion at the level of the diaphragm and 114 +/- 16.5 ms for occlusion near the level of the renal arteries. These times approximate the times in which the pulse travels from the tip manometer to the inflated balloons and back. Forward and reflected pressure and flow waves were calculated from reflection coefficients. Aortic occlusion caused larger reflected waves and the recorded wave forms were caused by the summation of forward and backward waves, the latter contributing the secondary pressure rise and the increased flow deceleration. Occlusion of both carotid arteries showed no specific reflection site but reflected waves were larger. This increased reflection can probably be explained as the result of greater total reflection from distributed sites under increased peripheral resistance.

Animals↗

PubMed2002

Metal strip reflectivity and NSPUDT orientations in langanite, langasite, and gallium phosphate.

New materials of the trigonal 32 class have received much attention recently, due to their quartz-like temperature behavior and the promise of higher electromechanical coupling coefficients. The magnitude and phase of the reflection coefficient of the metal strips that form the SAW transducers and reflector structures is a critical parameter that allows proper device designs and optimal material surface orientation. This paper describes an investigation of the magnitude and phase of the SAW metal strip reflectivity in some new materials and along new orientations. The materials are langanite, langasite, and gallium phosphate. The results are presented as contour plots of the magnitude and phase of the reflection coefficient. In addition, the phase velocity, temperature coefficient of delay, electromechanical coupling coefficient, and power flow angle are given, thus allowing proper orientation selection for SAW device designs. The results presented highlight the reflection coefficient calculations in the selection of natural single-phase unidirectional transducer orientations (NSPUDT) for these new materials. As a result of the present work, reflection coefficient magnitudes five times larger than those of the well-known quartz NSPUDT orientation (Euler angles: 0 degrees 132.75 degrees 25 degrees) can be obtained with the new materials, for orientations where the optimum NSPUDT reflection coefficient phase criterion is met. The new materials discussed here provide an opportunity to design shorter- and higher-bandwidth devices due to: the increased electromechanical coupling coefficient; the higher reflection coefficient; and the lower phase velocities; while maintaining the excellent temperature insensitivity characteristic of quartz. The orientation regions suggested in this paper for the new materials are thus very promising for low-loss, high-performance consumer and communications SAW designs, such as NSPUDT filters, resonator-based filters, and other devices that can benefit from a high metal strip reflectivity.

Journal Article↗

PubMed1999

The influence of early reflections on the identification and lateralization of vowels.

Sound coming directly from a source is often accompanied by reflections arriving from different directions. However, the "precedence effect" occurs when listeners judge such a source's direction: information in the direct, first-arriving sound tends to govern the direction heard for the overall sound. This paper asks whether the spectral envelope of the direct sound has a similar, dominant influence on the spectral envelope perceived for the whole sound. A continuum between two vowels was produced and then a "two-part" filter distorted each step. The beginning of this filter's unit-sample response simulated a direct sound with no distortion of the spectral envelope. The second part simulated a reflection pattern that distorted the spectral envelope. The reflections' frequency response was designed to give the spectral envelope of one of the continuum's end-points to the other end-point. Listeners' identifications showed that the reflections in two-part filters had a substantial influence because sounds tended to be identified as the positive vowel of the reflection pattern. This effect was not reduced when the interaural delays of the reflections and the direct sound were substantially different. Also, when the reflections were caused to precede the direct sound, the effects were much the same. By contrast, in measurements of lateralization the precedence effect was obtained. Here, the lateral position of the whole sound was largely governed by the interaural delay of the direct sound, and was hardly affected by the interaural delay of the reflections.

Humans↗

PubMed1993

Repeated reflection of waves in the systemic arterial system.

Traditional analysis of pulse-wave propagation and reflection in the arterial system treats measured pressure and flow waves as the sum of a single forward wave (traveling away from the heart) and a single backward wave (traveling toward the heart). The purpose of this study was to develop a more general wave reflection theory that allows repeated reflection of these waves. The arterial system was modeled as a uniform viscoelastic tube terminating in a complex load with reflections occurring at the tube load interface and the heart tube interface. The resulting framework considers the forward wave to be the sum of an initial wave plus a series of antegrade waves. Similarly, the backward wave is the sum of a series of retrograde waves. This repeated reflection theory contains within it the traditional forward/backward wave reflection analysis as a special case. In addition, the individual antegrade and retrograde waves, at the tube entrance, are shown to be independent of the tube length. Aortic pressure and flow data, from dog experiments, were used to illustrate the phenomenon of repeated reflections. Alteration of the arterial system loading conditions, brought about through pharmacological intervention, affected the number and morphology of repeated waves. These results are compared with those found in traditional forward/backward reflection analysis.

Animals↗

PubMed1996

Method for determining distribution of reflection sites in the arterial system.

We developed a new method to determine the location and importance of reflection sites in the arterial system. The method is based on the decomposition of the aortic pressure wave into its forward and backward components, and it provides the reflection profile of the arterial system as a wave reflection site amplitude versus distance from the heart. The reflection profile can be seen as the response of the arterial system to a pressure delta pulse where reflections upstream from the measurement location have been eliminated. The method was successfully tested on a simple model loaded with a pure resistor, a two-element windkessel, and a bifurcating tube system. It was then applied to the aortic pressure and flow signals measured in six mongrel dogs whose aorta was occluded at different levels. The profiles obtained from measurements at control showed two main reflection regions, one located in the vicinity (0.1-0.2 m) of the heart and the other located in the region of the iliac bifurcation. All occlusions, even the most distant one at the iliac bifurcation, could be identified in both amplitude (amount of reflections) and distance from the heart. The spatial resolution of the profiles was approximately 0.1 m as a result of the limited power spectrum contained in the arterial pulse, and the identification of reflection sites decreased rapidly with the distance.

Animals↗

PubMed1992

Increased systolic pressure in chronic uremia. Role of arterial wave reflections.

To assess the role of arterial wave reflections in the mechanism of systolic hypertension and altered pulsatile arterial dynamics in patients with end-stage renal disease (ESRD), 79 ESRD patients were compared with 73 age-matched control subjects with normal renal function and similar mean blood pressure. Wave reflections were investigated from the carotid pulse contour recorded by applanation tonometry using a Millar micromanometer-tipped probe. Wave reflections were quantified as the ratio (augmentation index, %) of the height of the late systolic peak to the total height of carotid pulse wave. Travel time of the reflected wave was timed from the foot of the pressure wave to the foot of the late systolic peak. Systolic and pulse pressure were increased in ESRD patients (p less than 0.001) and was not attributable to differences in left ventricular ejection pattern. The augmentation index was increased in ESRD patients (23.2 +/- 15.0 versus 9.8 +/- 15.6%; p less than 0.001) in association with a shorter travel time of reflected wave (109 +/- 24 versus 131 +/- 30 msec; p less than 0.001). Multiple regression analysis showed two principal factors associated (p less than 0.001) with the increase in augmentation index and shortened travel time of reflected wave: increased aortic pulse wave velocity and smaller stature with shorter body height in ESRD patients. The study points to the role of arterial wave reflections in the mechanisms producing alterations in pulsatile arterial dynamics in ESRD and is the first, through the mechanisms of early wave reflections, to show in humans that the increase in systolic and pulse pressures is associated with lesser body size.

Adult↗

PubMed1982

Pulse wave reflection: can it explain the differences between systemic and pulmonary pressure and flow waves? A study in dogs.

We have studied the effect of changes in pulse wave reflection on the configurations of pressure and flow in systemic and pulmonary circulation. Electromagnetic flow transducers, atrial catheters, and pacing leads were implanted in 10 dogs. In four animals, the flow transducer was placed on the pulmonary artery, in another four on the ascending aorta, and in two additional dogs on both vessels. One week later, ascending aortic and/or pulmonary artery flow and pressure (catheter tip manometer) were measured under general anesthesia (Nembutal, 30 mg/kg, iv). When the pulmonary circulation was studied (six dogs), measurements were made before and during serotonin infusion (0.5-0.75 mg/min). When the systemic circulation was studied (six dogs), measurements were made before and during nitroprusside infusion (50-200 micrograms/min). To quantify the arterial load, we calculated pulmonary and systemic input impedances. To estimate the amount of reflection, we used a reflection index which we defined as the amplitude ratio of reflected and forward wave. Nitroprusside decreased total peripheral resistance, increased total arterial compliance, and decreased the reflection index; similarity between aortic pressure and flow wave shapes increased, and they looked more like their pulmonary counterparts. Serotonin increased pulmonary vascular resistance, decreased pulmonary arterial compliance, and increased the reflection index. Resemblance of pressure and flow waves decreased. The differences in wave shapes can thus be explained by the amount of reflection: the less reflection the more pressure and flow resemble each other.

Animals↗

PubMed1991

Two arterial effective reflecting sites may appear as one to the heart.

The relation between reflected waves and features of ascending aortic pressure waveforms and impedance patterns was investigated with a modified T-tube model of the systemic arterial circulation. Ascending aortic pressure and flow and descending aortic flow were measured in 10 dogs under basal conditions and under the effect of an agent (methoxamine) that caused vasoconstriction and an increase of mean aortic pressure. A broad range of aortic pressure amplitudes and features was obtained. These waveshapes were classified into four groups. Under basal conditions, cases for which a prominent diastolic fluctuation was present (n = 8) were grouped in A. Cases for which this fluctuation was absent (n = 2) were grouped in B. Groups C (n = 4) and D (n = 3) included cases that, under vasoconstricted conditions, did or did not display, respectively, a diastolic fluctuation in pressure. Arterial T-tube model parameters were estimated by simultaneously fitting the model to both ascending and descending aortic flow with aortic pressure as input. A good fit was obtained in any case considered. After parameter estimation, forward and reflected waves and impedance patterns at the entrance of head circulation (head and upper limbs) and body circulation (trunk and lower limbs) as well as their merger in the ascending aorta were determined. T-tube input impedance compared well with impedance data points obtained from the ratio of corresponding harmonics of ascending aortic pressure and flow. In some cases (group A), modulus and phase spectra displayed two distinct minima, in the range from 0 to 10 Hz. In some other circumstances, these minima were less distinct (groups B and C) and could even appear as one (group D). Whether one or two minima appeared in the ascending aortic impedance spectra at low frequency and whether a prominent diastolic fluctuation did or did not appear in aortic pressure, pressure and flow waveshapes proximal to the heart were explained by the presence of two effective reflecting sites in the systemic circulation. In group B, a diastolic fluctuation in pressure was absent despite the fact that head-end and body-end reflected waves were distinct. This happened because body-end reflected waves peaked corresponding to a minimum of the head-end reflected wave. In group D, a diastolic fluctuation in aortic pressure was absent because the body-end reflected wave moved into systole and superimposed on the head-end reflected wave. This superimposition was due to increased pulse wave velocity in the body transmission path as a result of decreased arterial distensibility.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2000

A model for facilitation of critical reflective practice: Part I--Introductory discussion and explanation of the phases followed to construct the model.

The purpose of this inquiry was to construct a model for facilitation of critical reflective practice, based on thorough analysis of the main concepts (critical thinking and reflection), related viewpoints, models and theories; and the data gathered and analyzed during, the naturalistic inquiry. The constructed model evolved from empirical observations, intuitive insights of the inquirer and from deductions combining ideas from several fields of inquiry. The model for facilitation of critical reflective practice postualates that practitioners have the inherent potential to change from auto-pilot practice to critical reflective practice. The purpose of the model is the facilitation of heightened awareness of the self, to enable health care professionals to consciously meet community needs and expectations. The desired outcome is transformative intellectuals who will strive to empower others to become critical reflective learners and practitioners themselves. The process followed during the construction of the model and the constructed model will be discussed in three (3) articles, namely: A model for facilitation of critical reflective practice: Part I--Introductory discussion and explanation of the phases followed to construct the model. A model for facilitation of critical reflective practice: Part II--Conceptual analysis within the context of constructing the model. A model for facilitation of critical reflective practice: Part III--Description of the model.

Attitude of Health Personnel↗