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PubMed1999

Applications of the causality condition to one-dimensional acoustic reflection problems.

The causality condition is examined as a means of determining frequency-domain information about a submerged object from a partial knowledge of its acoustic reflection characteristics. A one-dimensional problem is considered in which an acoustic wave reflects from an object that is described by the impedance it presents to the fluid. Two new applications of the causality condition to the frequency-domain analysis of this problem are investigated and illustrated by numerical examples. In each application, the causality condition is used to find the object's complex impedance from a knowledge of the reflected wave's magnitude. The first application is to experimental studies where one desires a knowledge of an object's complex impedance but practical limitations only allow a measurement of the reflected wave amplitude. Analysis shows that the causality condition may be used to determine the phase of the reflected wave, and hence the object's impedance, if the reflection coefficient is minimum phase. When this is true, examples suggest that the phase of the reflection coefficient may be accurately determined from the causality condition even in the presence of noise and band-limited data. The second application is to design situations, where one wishes to create an object that reflects sound with a specified frequency-dependent magnitude. The causality condition may aid the designer by providing a knowledge of all causal object impedances that produce the same reflection coefficient magnitude. A numerical example is presented in which a variety of causal object impedances produce the same reflection coefficient magnitude over an infinite frequency range.

Acoustics↗
PubMed2001

Constructive and destructive addition of forward and reflected arterial pulse waves.

Although the physics of arterial pulse wave propagation and reflection is well understood, there is considerable debate as to the effect of reflection on vascular input impedance (Z(in)), pulsatile pressure, and stroke work (SW). This may be related to how reflection is studied. Conventionally, reflection is experimentally abolished (thus radically changing unrelated parameters), or a specific model is assumed from which reflection can be removed (yielding model-dependent results). The present work proposes a simple, model-independent method to evaluate the effect of reflection directly from measured pulsatile pressure (P) and flow (Q). Because characteristic impedance (Z(0)) is Z(in) in the absence of reflection, the P with reflection theoretically removed can be calculated from Q x Z(0). Applying this insight to an illustrative case indicates that reflection has the least effect on P and SW at normal pressure but a greater effect with vasodilation and vasoconstriction. Z(in), P, and SW are increased or decreased depending on the relative amount of constructive and destructive addition of forward and reflected arterial pulse waves.

Animals↗
PubMed1987

Arterial wave reflection in heart failure.

Arterial wave reflection may adversely influence both left ventricular afterload and ejection performance. Therefore, using multisensor catheter manometers, we derived wave reflection indexes from ascending aortic pressure and velocity recordings in 17 subjects with clinical heart failure secondary to idiopathic dilated cardiomyopathy and 11 control subjects free of detectable cardiovascular disease. Patients were studied at rest as well as during submaximal supine bicycle exercise. Eight of the subjects with cardiomyopathy were also studied during infusion of nitroprusside at rest and on exercise. Reflection indexes decreased on exercise in normal subjects but did not consistently do so in the subjects with heart failure. In both groups the reflected wave on exercise returned earlier during the ejection period. Infusion of nitroprusside at rest in subjects with heart failure had dramatic, and significant, effects on the magnitude and timing of arterial wave reflections. The effect of nitroprusside on reflection magnitude persisted on exercise, although the timing of the reflected wave was disadvantageous. The systemic arterial response to exercise in heart failure is characterized by a smaller change in wave reflection indexes in spite of a comparable decrease in systemic vascular resistance. Nitroprusside diminishes the potentially adverse impact of wave reflections by decreasing the magnitude of the reflected wave and altering its timing. Additional dose titration studies are necessary to fully assess the benefits of pharmacologic vasodilation during exercise.

Adult↗
PubMed1992

Reflection after delayed excitation in a computer model of a single fiber.

Reflection (reflected reentry) is a case of reentry in a one-dimensional structure, divided into proximal and distal segments, in which tissue excited by a wave front propagating in a forward direction is reexcited by electrical activity coming backward from the original direction of propagation. Cases of reflection have been demonstrated in Purkinje fibers and in ventricular muscle preparations containing multiple fibers. Several mechanisms possibly responsible for reflected reentry have been proposed. However, the difficulty in the interpretation of the experimental results, as well as the limited number of different conditions in which reflection was obtained, has kept open the question about conditions and mechanisms for reflection. We have developed a computer model in which reflection occurs. The model involves a single fiber and uses the DiFrancesco-Noble equations for the Purkinje fiber to model the ionic currents. The results show that reflection is possible in a single fiber and that diastolic depolarization (automaticity) is not a requirement for reflection. Active membrane responses to a just-above-threshold stimulus were important for achieving the necessary time delay. Systematic simulations showed further that reflection occurred only when the right coupling conditions linked a short or long proximal fiber to a short distal segment.

Action Potentials↗
PubMed2005

In vitro multispectral diffuse reflectance measurements of the porcine fundus.

PURPOSE: To quantify the reflectance of the swine fundus as a function of illumination angle and wavelength using a novel technique of intravitreal illumination. METHODS: Enucleated swine eyes were illuminated with a scanning monochromator coupled to a fiber-optic probe placed in the vitreous at several locations. Intravitreal illumination was used to reduce the effects of extraneous reflections and scatter from the anterior structures of the eye, including glints from the internal limiting membrane and blood vessels. Intravitreal illumination provided different light paths and additional information to apply to retinal reflectance modeling. A 25-mm(2) region of the illuminated fundus was imaged while the angle of illumination was varied over a maximum range of 22 degrees . Multispectral images from areas free of large blood vessels were acquired. The diffusely reflected intensity was integrated over the pupil with a solid angle of 0.028 steradians. The spectral reflectance function was calculated for multiple illumination angles. RESULTS: Multispectral fundus image sets were obtained for two enucleated swine eyes by using intravitreal illumination. The fundus spectral reflectance function showed decreasing reflectance with increasing illumination angle, rapid changes in the 430- to 480-nm range, and a fairly consistent reflectance decrease for 480 to 700 nm. CONCLUSIONS: Variations in fundus spectral reflectance with change in the illumination angle were found to deviate from Lambertian behavior, varying from Lambertian by 5% across the spectrum in one sample and 20% in a second sample. Intravitreal illumination resulted in markedly decreased extraneous reflections.

Animals↗
PubMed2001

Accuracy of Kubelka-Munk reflectance theory applied to human dentin and enamel.

The Kubelka-Munk (K-M) theory provides a reflectance model for translucent materials placed on backings of different colors. We hypothesize that Kubelka-Munk (K-M) theoretical diffuse reflectance spectra of dentin and enamel are in good agreement with observed diffuse reflectance. The aim of this study was to measure the reflectance of enamel and dentin specimens and to compare the measured values of reflectance with K-M theoretical values. Disc-shaped specimens of enamel, dentin, and enamel/dentin were prepared from extracted teeth. Diffuse reflectance spectra were measured on three backings by means of a reflectance spectrophotometer over every wavelength (lambda) from 400 to 700 nm at three thicknesses. The measured reflectance values were fit by non-linear regression to corrected K-M theory. The low value of the reported errors associated with the application of K-M theory illustrated that the theoretical diffuse reflectance spectra of dentin and enamel are in good agreement with the observed diffuse reflectance.

Absorption↗
PubMed2003

Method for high-accuracy reflectance measurements in the 2.5-microm region.

Reflectance measurement with spectroradiometers in the solar wavelength region (0.4-2.5 microm) are frequently conducted in the laboratory or in the field to characterize surface materials of artificial and natural targets. The spectral surface reflectance is calculated as the ratio of the signals obtained over the target surface and a reference panel, yielding a relative reflectance value. If the reflectance of the reference panel is known, the absolute target reflectance can be computed. This standard measurement technique assumes that the signal at the radiometer is due completely to reflected target and reference radiation. However, for field measurements in the 2.4-2.5-microm region with the Sun as the illumination source, the emitted thermal radiation is not a negligible part of the signal even at ambient temperatures, because the atmospheric transmittance, and thus the solar illumination level, is small in the atmospheric absorption regions. A new method is proposed that calculates reflectance values in the 2.4-2.5-microm region while it accounts for the reference panel reflectance and the emitted radiation. This technique needs instruments with noise-equivalent radiances of 2 orders of magnitude below currently commercially available instruments and requires measurement of the surface temperatures of target and reference. If the reference panel reflectance and temperature effects are neglected, the standard method yields reflectance errors up to 0.08 and 0.15 units for 7- and 2-nm bandwidth instruments, respectively. For the new method the corresponding errors can be reduced to approximately 0.01 units for the surface temperature range of 20-35 degrees C.

Journal Article↗
PubMed2005

Modeling total and polarized reflectances of ice clouds: evaluation by means of POLDER and ATSR-2 measurements.

Four ice-crystal models are tested by use of ice-cloud reflectances derived from Along Track Scanning Radiometer-2 (ATSR-2) and Polarization and Directionality of Earth's Reflectances (POLDER) radiance measurements. The analysis is based on dual-view ATSR-2 total reflectances of tropical cirrus and POLDER global-scale total and polarized reflectances of ice clouds at as many as 14 viewing directions. Adequate simulations of ATSR-2 total reflectances at 0.865 microm are obtained with model clouds consisting of moderately distorted imperfect hexagonal monocrystals (IMPs). The optically thickest clouds (tau > approximately 16) in the selected case tend to be better simulated by use of pure hexagonal monocrystals (PHMs). POLDER total reflectances at 0.670 microm are best simulated with columnar or platelike IMPs or columnar inhomogeneous hexagonal monocrystals (IHMs). Less-favorable simulations are obtained for platelike IHMs and polycrystals (POLYs). Inadequate simulations of POLDER total and polarized reflectances are obtained for model clouds consisting of PHMs. Better simulations of the POLDER polarized reflectances at 0.865 microm are obtained with IMPs, IHMs, or POLYs, although POLYs produce polarized reflectances that are systematically lower than most of the measurements. The best simulations of the polarized reflectance for the ice-crystal models assumed in this study are obtained for model clouds consisting of columnar IMPs or IHMs.

Journal Article↗
PubMed2006

Reflectance and transmittance model for recto-verso halftone prints.

We propose a spectral prediction model for predicting the reflectance and transmittance of recto-verso halftone prints. A recto-verso halftone print is modeled as a diffusing substrate surrounded by two inked interfaces in contact with air (or with another medium). The interaction of light with the print comprises three components: (a) the attenuation of the incident light penetrating the print across the inked interface, (b) the internal reflectance and internal transmittance that accounts for the substrate's intrinsic reflectance and transmittance and for the multiple Fresnel internal reflections at the inked interfaces, and (c) the attenuation of light exiting the print across the inked interfaces. Both the classical Williams-Clapper and Clapper-Yule spectral prediction models are special cases of the proposed recto-verso reflectance and transmittance model. We also extend the Kubelka-Munk model to predict the reflectance and transmittance of recto-verso halftone prints. The extended Kubelka-Munk model is compatible with the proposed recto-verso reflectance and transmittance model. In the case of a homogeneous substrate, the recto-verso model's internal reflectance and transmittance can be expressed as a function Kubelka-Munk's scattering and absorption parameters, or the Kubelka-Munk's scattering and absorption parameters can be inferred from the recto-verso model's internal reflectance and transmittance, deduced from spectral measurements. The proposed model offers new perspectives both for spectral transmission and reflection predictions and for characterizing the properties of printed diffuse substrates.

Journal Article↗
PubMed2004

Reflective thinking in clinical nursing education: a concept analysis.

Over decades nursing had an interest in clarifying and developing its knowledge base and its conceptual foundation. Reflective thinking has become a popular word in nursing education world wide, but its meaning and effective use remains debatable because of lack of clarity in its meaning (Mackintosh, 1998:553). The researcher engaged in the concept analysis of reflective thinking so as to fully understand its meaning and interpretation, hence the research question to be addressed by this article is: "What is the meaning of reflective thinking in clinical nursing education?" This article seeks to explore and describe the conceptual meaning of reflective thinking in clinical nursing education using the method of concept analysis as outlined by Wilson (1963:23-39) and Gift (1997:75,76). Concept analysis of reflective thinking constitutes the first phase of a study to develop a model to facilitate reflective thinking in clinical nursing education, thus ensuring theoretical validity of the model. An extensive examination of domain specific and various disciplines' literature was explored as part of the concept analysis. A selection of information regarding variations and similarities in the use and interpretation of reflective thinking across clinical nursing education was drawn from computerised data bases. This increased the rigor and the findings of the analysis. Through deductive reasoning and drawing of inferences, attributes were clustered in an attempt to identify the apparent essence of the concept. Three categories and the related connotations emerged as follows: Antecedents (Cognitive and affective thinking skills). Process (The three phases of reflective thinking). Outcome ( New insight and changed perspective). Reflective thinking was considered from the result of concept analysis as a cyclic, interactive constructing mental process to improve practice in a specific context. It is recommended that a model to facilitate reflective thinking in clinical nursing education be developed based on the results of this concept analysis.

Cognition↗
PubMed2001

Advancing the quality of oncology nursing care: Interlink Community Cancer Nurses' model for reflective practice.

Since 1996, Interlink Community Cancer Nurses have been using reflective practice as a team to share knowledge and experience amongst peers. The use of reflective practice enables the nurse to examine decision-making in patient situations and uncover the knowledge and artistry that is embedded in nursing practice. This article describes how reflection is practised by specialist cancer nurses to advance the quality of caregiving. The use of a structured framework for reflection which incorporates ways of knowing in nursing is an essential feature of the Interlink model for reflection. The development of a process for reflection within the Interlink program has at times been challenging. However, the Interlink nurses' experience with reflection is believed to be critical to the ongoing development of the program and the individual nurse. Interlink nurses have found that guided reflection, the creation of an environmental milieu for reflection and personal knowing, and self-evaluation are critical to the process of becoming a self-reflective practitioner.

Caregivers↗
PubMed1999

Directional and spectral reflectance of the rat retinal nerve fiber layer.

PURPOSE: To measure and describe the reflectance properties of a mammalian retinal nerve fiber layer (RNFL) and to determine the mechanisms responsible for the RNFL reflectance. METHODS: An isolated rat retina suspended across a slit in a black membrane and mounted in a black perfusion chamber provided high quality images of the RNFL. Imaging microreflectometry was used to measure RNFL reflectance at wavelengths from 400 nm to 830 nm and as a function of illumination angle. RESULTS: The directional reflectance of rat RNFL at all wavelengths was consistent with the theory of light scattering by cylinders; each nerve fiber bundle scattered light into a conical sheet coaxial with the bundle. There was no evidence of a noncylindrical component at any wavelength. Measured reflectance spectra were consistent between animals, similar to ones previously measured in macaque, and varied with scattering angle. All spectra could be described by a two-mechanism cylindrical scattering model with three free parameters. CONCLUSIONS: At all wavelengths the reflectance of rat RNFL arises from light scattering by cylindrical structures. The highly directional nature of this reflectance can be an important source of measurement variability in clinical assessment of the RNFL. The reflectance spectra reveal a combination of mechanisms: At wavelengths shorter than approximately 570 nm the reflectance comes from cylinders with diameters much smaller than the wavelength, but at wavelengths longer than approximately 680 nm the reflectance comes from cylinders with effective diameters of 350 nm to 900 nm.

Animals↗
PubMed1999

[Concept analysis of reflective thinking].

The nursing practice is described as a scientific practice, but also as a practice where caring is important. The purpose of nursing education is to provide competent nursing practitioners. This implies that future practitioners must have both critical analytical thinking abilities, as well as empathy and moral values. Reflective thinking could probably accommodate these thinking skills. It seems that the facilitation of reflective thinking skills is essential in nursing education. The research question that is relevant in this context is: "What is reflective thinking?" The purpose of this article is to report on the concept analysis of reflective thinking and in particular on the connotative meaning (critical attributes) thereof. The method used to perform the concept analysis is based on the original method of Wilson (1987) as described by Walker & Avant (1995). As part of the concept analysis the connotations (critical attributes) are identified, reduced and organized into three categories, namely pre-requisites, processes and outcomes. A model case is described which confirms the essential critical attributes of reflective thinking. Finally a theoretical definition of reflective thinking is derived and reads as follows: Reflective thinking is a cyclic, hierarchical and interactive construction process. It is initiated, extended and continued because of personal cognitive-affective interaction (individual dimension) as well as interaction with the social environment (social dimension). to realize reflective thinking, a level of internalization on the cognitive and affective domain is required. The result of reflective thinking is a integrated framework of knowledge (meaningful learning) and a internalized value system providing a new perspective on and better understanding of a problem. Reflective thinking further leads to more effective decision making- and problem solving skills.

Decision Making↗
PubMed2005

[Studies on relics conservation by diffuse reflectance spectroscopy].

A diffuse reflectance spectroscopic method was developed to investigate relics conservation with a self-made fiber optics reflectance spectrophotometer. With this technique (1) identifying pigments on the color relics was done by comparing the shapes of reflectance spectra and the positions of reflectance peaks or first derivative peaks with those of related standard pigments; (2) changes of surface states of metals were monitored. From the investigation on the reflectance spectra of copper and its rust product, we can easily get some information about the metal surface, so diffuse reflectance spectroscopy shows special function in the research on metal surface; (3) the diffuse reflectance spectroscopic characteristics of the materials used in protection and restoration of cultural heritages were studied, which can help us choose proper protecting and restoring materials. From our studies it was verified that diffuse reflectance spectroscopy is a quick, simple and non-destructive analytical technique. The study makes diffuse reflectance spectroscopy a new means for relic protection, and opens a new application area for diffuse reflectance spectroscopy as well.

Coloring Agents↗
PubMed2004

Knowledge translation: the role and place of practice reflection.

Reflection is the mechanism by which we contemplate and try to understand relatively complex and sometimes troubling ideas for which there is no obvious solution. Reflection allows us to transform current ideas and experiences into new knowledge and action. Personal experiences and organizational feedback can trigger reflection, whereas a lack of time, available colleagues, and social networks detract from the ability professionals have to reflect. Educational programs can encourage reflection through the judicious use of case-based discussion, formal and informal needs assessments, and commitment to change exercises. Learning journals and personal learning projects are self-directed methods that facilitate reflection. In the workplace, critical incident techniques and debriefing of cases provide opportunities for thoughtful inquiry. Additional study is needed to understand how and why reflection works to transform surface learning into deep learning and change in practice; how reflection enhances the integration of reading, collegial interchange, and classroom discussion into practice; and how technology can enhance reflection.

Education, Medical↗
PubMed2004

Determination of the peritoneal reflection using intraoperative proctoscopy.

PURPOSE: Rectal carcinomas are amenable to transanal excision in 3 to 5 percent of cases. Location below the peritoneal reflection is one requirement for transanal excision and transanal endoscopic microsurgery. The location of the peritoneal reflection has not been extensively studied in living patients. METHODS: This study investigated the location of the peritoneal reflection in 50 patients undergoing laparotomy. The distance from the anal verge to the peritoneal reflection was measured in each patient via simultaneous intraoperative proctoscopy and intra-abdominal visualization of the peritoneal reflection. The mean distance to the peritoneal reflection, range of measurements, and complications of proctoscopy were recorded. RESULTS: Intraoperative proctoscopy was performed on 50 patients after informed consent. The mean lengths of the peritoneal reflection were 9 cm anteriorly, 12.2 cm laterally, and 14.8 cm posteriorly for females, and 9.7 cm anteriorly, 12.8 cm laterally, and 15.5 cm posteriorly for males. The lengths of the anterior, lateral, and posterior peritoneal measurements were statistically different from one another, regardless of gender (P < 0.01). There were no complications of proctoscopy. CONCLUSIONS: Our data indicated that the peritoneal reflection is located higher on the rectum than reported in autopsy studies, and that there is no difference between males and females. Knowledge of the location and position of a rectal carcinoma in relationship to the peritoneal reflection will help the surgeon optimize the use of transanal techniques of resection.

Adult↗
PubMed2005

Changes in spectral reflectance of wheat leaves in response to specific macronutrient deficiency.

In wheat (Triticum aestivum L.) plants, deficiency of an essential element may drastically affect growth, appearance, and most importantly yield. Wheat, the focus of this study, is one of the crops studied in the CELSS program. Information about nutrient deficiencies in crops grown in controlled environment is essential to optimize food productivity. The main objective of this study was to determine whether deficiency of Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca) and Magnesium (M) alters spectral reflectance properties of wheat leaves. Plants were grown in the greenhouse and growth chamber, in a modified Hoagland's nutrient solution. Spectral reflectance of fully expanded wheat leaves from 280 to 1100 nm, nutrient concentrations (N, P, K, and Ca) and chlorophyll (Chl) were determined when deficiency symptoms were first evident (approximately 6-7 weeks). Chlorophyll content and fresh and dry weight, were used to assess the severity of the nutrient stress. All nutrient deficiencies affected chlorophyll content and generally increased reflectance in the visible (VIS) 400-700 nm and infrared (IR) 700-1100 nm ranges. Magnesium and nitrogen deficiencies had the most pronounced effect on chlorophyll concentration height, and reflectance. All macronutrient deficiencies tested reduced chlorophyll concentration, increase reflectance in the visible range and caused a shift in the position of the red edge (the point of maximum slope on the reflectance spectrum of vegetation between red and near-infrared wavelengths) toward shorter or longer wavelengths; depending upon the element. In the greenhouse, N and Mg induced the greatest increase in reflectance of 33% and 25% in the VI range and 86% and 53% in the IR range, respectively. However, in the growth chamber, an increase of 97% and 25% occurred in the VI range, and 20% and 33% in the IR range, respectively. In the IR range in the growth chamber, P, K, and Ca deficiency caused a reduction in reflectance (412-770 nm). This research indicates that mineral deficiencies and reflectance are not specific to one environment and could have important implications for the design of CELSS in space, and perhaps the future of terrestrial agriculture.

Biomass↗
PubMed2001

Estimation of radiance reflectance and the concentrations of optically active substances in Lake Mälaren, Sweden, based on direct and inverse solutions of a simple model.

A semi-analytical model which predicts radiance reflectance just below the water surface (Lu/Ed 0-) has been developed and used to predict the spectral variability of radiance reflectance in Lake Mälaren, Sweden. Radiance reflectance is predicted as a function of the optically active substances in the water, which include the concentrations of chlorophyll-a + phaeophytin-a, suspended particular inorganic material (SPIM), suspended particulate organic material (SPOM), and dissolved yellow substances. These substances are linked to the absorption and backscattering coefficients through a series of empirical relationships, and ultimately radiance reflectance is estimated as a function of the ratio of backscattering to absorption. Parameterization of the model, i.e. the development of the empirical relationships linking the optically active substances to the inherent optical properties (IOPs), is based on both in situ measurements and laboratory analyses. We have collected data that allowed us to examine the potential variability in radiance reflectance, as predicted by our model, due to both variations in the optically active substances, and in the model parameterization. Simulations based on a data set collected during the fall of 1997 from 12 sites, which span a large range in water quality (secchi depth 0.8-5.0 m), suggest that, with the proper parameterization, the model can accurately predict the spectra of radiance reflectance as a function of the concentration of optically active substances. Variations in the concentrations of optically active substances accounted for a large portion of the total simulated variability in radiance reflectance (i.e. that resulting from variations in parameterization and in the concentrations of optically active substances). However, the measured variability in parameterization could account for up to 50% of the total variability in simulated radiance reflectance. This suggests that variability in the model parameterization, arising from both real variability and experimental error, will limit the use of this model for interpreting remote sensing data. Nevertheless, inverse solutions of the model are able to estimate the concentrations of chlorophyll, suspended inorganic material (SPIM) and the absorption of yellow substances from measured radiance reflectance spectra The average error for the 12 sites was a -0.07 for chlorophyll, -0.15 for dissolved yellow substances (measured as the absorption at 400 nm) and 0.07 for SPIM, even though individual errors could be as great as 50%.

Chlorophyll↗