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PubMed2005

Reflections on some unresolved issues in hypnosis.

Reflections guided the author in the preparation of this paper. Having worked in and around the construction "hypnosis" for two thirds of a century, he can claim the privilege of offering reflections rather than presenting new data or revised theories. His reflections include some autobiographical accounts that help illuminate how he came to construe the conduct traditionally subsumed under the hypnosis label as the enactment of a social role mediated by skill in imagining.

Humans↗

PubMed1976

Reflection-impulsivity and need for achievement in emotionally disturbed children.

Reflection-impulsivity is the cognitive dimension proposed by Kagan and his colleagues to describe the differences in children's resolution to response uncertainty. Impulsive children tend to respond quickly without considering all of the available alternatives and consequently make many mistakes. Reflecttive children consider all of the available alternatives, withhold responding until they have a high probability of being correct, and consequently make few mistakes. The primary dynamic underlying a reflective cognitive style is hypothesized to be a fear of making a mistake: the greater the fear, the more reflective the child is and the more cautiously he performs. On the other hand, minimal anxiety over a potentially inaccurate answer is likely to result in an impulsive performance.

Achievement↗

PubMed2003

Reflective critique and collaborative practice in evaluation: promoting change in medical education.

The School of Medicine at the University of Tasmania has recently begun to implement a process of curriculum evaluation,which aims to reflect contemporary best practice in evaluation in tertiary pedagogy and medical education. Best practice must accommodate a broadening interest in cooperative and collaborative evaluation strategies among stakeholders, advances in applied qualitative educational research and recognition that critical reflection on practice is the cornerstone of professional education. This paper reports a recent evaluation strategy in a specific year-long unit in the second year of a six-year undergraduate medical degree. The paper begins by presenting the context; it then discusses and rationalises the evaluation strategy and presents findings. The paper concludes by arguing that curriculum evaluation as best practice must be reflective, informed by the scholarship of medical education, and internalized as a dynamic process that can promote sustainable change and improvement in medical curricula. Such an approach will contribute to an undergraduate medical curriculum that prepares students for the demands and complexities of medical practice.

Cooperative Behavior↗

PubMed2000

Reduction of multiple reflection influence in microwave free-space measurements

The influence of the multiple reflections is one of the main error sources in the microwave free-space measurements. In this study, the influence is analyzed for the conventional free-space method, and a new method which uses absorbing material inserted between the antenna and the sample to reduce the influence of the multiple reflections is proposed. The effectiveness of this approach is verified by measuring the attenuation of timbers. It is showed that the maximum error caused by the multiple reflections in the improved free-space set-up is 0.4 dB, while that in the conventional free-space method is 1.5 dB.

Journal Article↗

PubMed2007

Subtypes of rumination in adolescence: associations between brooding, reflection, depressive symptoms, and coping.

Prior research has indicated that rumination contributes to the maintenance or intensification of depressive symptoms among adults. This study examined associations between rumination and depressive symptoms in early adolescence. Using a short-term longitudinal design, we evaluated relations between subtypes of rumination and both depressive symptoms and coping among a community sample of 168 adolescents (70 boys, 98 girls, age M= 13.58). Results provided support for brooding and self-reflective subtypes of rumination. Brooding, but not reflection, predicted the development of depressive symptoms over time, particularly for girls. Brooding was related to maladaptive disengagement coping strategies, whereas reflection was related to adaptive primary and secondary coping strategies. These results suggest that not all types of self-focus on emotion contribute to the maintenance or intensification of depressive symptoms.

Adaptation, Psychological↗

PubMed2001

A comparison of reflectance and transmittance near-infrared spectroscopic techniques in determining drug content in intact tablets.

Drug contents of intact tablets were determined using non-destructive near infrared (NIR) reflectance and transmittance spectroscopic techniques. Tablets were compressed from blends of Avicel PH-101 and 0.5% w/w magnesium stearate with varying concentrations of anhydrous theophylline (0, 1, 2, 5, 10, 20 and 40% w/w). Ten tablets from each drug content batch were randomly selected for spectral analysis. Both reflectance and transmittance NIR spectra were obtained from these intact tablets. Actual drug contents of the tablets were then ascertained using a UV-spectrophotometer at 268 nm. Multiple linear regression (MLR) models at 1116 nm and partial least squares (PLS) calibration models were generated from the second derivative spectral data of the tablets in order to predict drug contents of intact tablets. Both the reflectance and the transmittance techniques were able to predict the drug contents in intact tablets over a wide range. However, a comparison of the results of the study indicated that the lowest percent errors of prediction were provided by the PLS calibration models generated from spectral data obtained using the transmittance technique.

Bronchodilator Agents↗

PubMed1983

Persistence of the mitogenic response to platelet-derived growth factor (competence) does not reflect a long-term interaction between the growth factor and the target cell.

Quiescent BALB/c-3T3 cells exposed briefly to platelet-derived growth factor (PDGF) become "competent" to replicate their DNA even if PDGF is removed from cell culture medium prior to the onset of DNA synthesis. We have suggested that persistence of the PDGF-induced competent state reflects a rapidly induced and relatively stable biochemical change within the target cells. Others suggest that the phenomenon reflects a long-term association between PDGF and its target cells or perhaps between PDGF and the cell culture dish. This controversy has been addressed (a) by examining the effect of anti-PDGF antibodies on PDGF-induced competence and (b) by studying the chemical fate of 125I-labeled PDGF. Anti-PDGF antibodies inactive both soluble and surface-bound PDGF. However, if quiescent 3T3 cells are exposed to PDGF for as little as 30 min, subsequent addition of these antibodies to the culture medium does not prevent the mitogenic response. Under conditions where the PDGF-induced competent state decays stochastically with a t1/2 of 18-20 h, cell-associated 125I-PDGF decays with a t1/2 of approximately 50 min. These data do not support the concept that persistence of the PDGF-induced competent state reflects a long-term association between PDGF and the target cells or between PDGF and the culture dish.

Animals↗

PubMed1986

Numerical considerations for interface reflections in medical ultrasound.

The original concept of the echo mechanism in diagnostic medical ultrasound--of step impedance discontinuities--is investigated in terms of the numerical implications of more refined models. The effect of a discontinuity in the attenuation coefficients is found to have as much significance as the impedance discontinuity at low reflection interfaces. An approximate analytical model is developed for spatially varying changes in the impedance. Numerical calculations are presented for reflections from delta-function and Gaussian-envelope RF pulses for two different models: an impedance gradient, and a connective tissue layer. The models used are well documented in acoustics textbooks, but the numerical results for typical tissue parameters show that a wide variety of interface structures may give rise to reflected amplitudes in the same range as that determined by the step impedance model. It is suggested that experimental investigation of interface structures may increase our understanding of the tissue: ultrasound interaction in diagnostic processes.

Humans↗

PubMed1987

The effect of surface finish on the reflection of CO2 laser beams from specula.

A potential source of hazard during gynaecological surgery with a CO2 laser is the reflection of the laser beam from the surfaces of the metal speculum. An experimental method of measuring the levels of radiation reflected from a variety of surfaces is described. Results which compare the effectiveness of different surface treatments in reducing reflections and show how this varies over a range of angles of incidence are presented. The significance of the results in terms of hazards to patients and staff is discussed.

Carbon Dioxide↗

PubMed1988

Reflection of laser light from ophthalmic contact lenses.

Reflections of laser radiation from ophthalmological contact lenses are measured and hazard analysis calculations are presented. Measurements were made on the contact lenses using ophthalmic argon and krypton lasers. Reflection coefficients were around 0.2% for lenses with 'anti-laser' coatings and in the region of 4% for uncoated lenses. It can be shown that the nominal ocular hazard distance for a typical ophthalmic argon laser beam reflected from a contact lens with a flat front surface is approximately 30 cm for a coated lens and 1 m for an uncoated lens. The necessity of protective glasses for attending staff in particular circumstances is reviewed.

Contact Lenses↗

PubMed1988

Weak reflection of a wave by a one-dimensional array of randomly spaced elements, with reference to the scattering of ultrasound by blood.

The mean reflection coefficient is deduced for a line of elements each of the same thickness, placed at random between two fixed ends, where the reflection coefficient of each element is very small. This theory is applied to the problem of the scattering of ultrasound by blood, and some qualitative agreement with experimental data is found. A simplified theory is also presented, from which the variance of the reflection coefficient is given.

Blood↗

PubMed1989

A portable scanning reflectance spectrophotometer using visible wavelengths for the rapid measurement of skin pigments.

A portable rapid scan reflectance spectrometer (400-700 nm in 2.8 s) has been developed for the measurement of cutaneous pigments. The instrument incorporates a tungsten halogen lamp light source, light transmission by fibre optics and wavelength selection by a circular variable wavelength interference filter. A microcomputer controls the instrument and processes the data. The performance of the instrument was evaluated by undertaking in vitro measurements of the reflectance spectra of blood. An index of the haemoglobin content of the sample based on the gradients of the log inverse reflectance spectrum between isobestic points at 527.5, 544 and 573 nm was devised and shown to be independent of the oxygenation of the haemoglobin. The haemoglobin index was combined with measurements at 558.5 nm, a wavelength at which absorbance is sensitive to the oxygenation of haemoglobin, to give a measure of oxygen saturation. The parameter was validated by determining the oxygen dissociation curve of red cells in plasma in vitro at pH 7.33, 37 degrees C and under a partial pressure of 40 mmHg of CO2.

Erythrocytes↗

PubMed1990

An investigation of factors affecting the accuracy of in vivo measurements of skin pigments by reflectance spectrophotometry.

Factors affecting the accuracy of the in vivo measurement of cutaneous pigments and blood oxygenation by reflectance spectrophotometry have been examined. It was found that stray light, the amounts of haemoglobin and melanin, and the level of blood oxygenation all contributed to the measured reflectance and had to be taken into account when calculating quantitative indices of skin pigments. Measurements on isolated sheets of epidermis demonstrated that over 50% of normally incident radiation is transmitted in a forward direction within 17 degrees of the incident direction and approximately 20% is backscattered between 90 degrees and 180 degrees out of the sample, approximately 6.0% of it by specular reflection at the surface. The effective optical pathlength in suspensions of whole red cells was found to be 7% greater than in simple solutions containing the same concentration of haemoglobin.

Hemoglobins↗

PubMed1993

A computerized autofluorescence and diffuse reflectance spectroanalyser system for in vivo skin studies.

A microcomputer-controlled spectroanalyser system has been set up to study optical properties of normal and abnormal human skin in vivo. The system can measure both tissue autofluorescence and diffuse reflectance at selected skin locations. The sample holder allows adjustment of the incident angle of the illumination light and the pick-up angle of the collected light providing the means to examine different depths of skin tissue. Using this system, we detected measurable skin autofluorescence with a maximum at about 470 nm when excited with 380 nm UV radiation. In this work, we also show that the absorption and scattering properties of the skin tissue (which can be determined from the measured diffuse reflectance spectrum) affect the shape of the autofluorescence spectrum. We believe that the combination of autofluorescence and diffuse reflectance measurements will lead to better understanding of the optical properties of normal and abnormal skin tissue.

Computer Systems↗

PubMed1998

Applicability of the Kubelka-Munk theory for the evaluation of reflectance spectra demonstrated for haemoglobin-free perfused heart tissue.

Reflectance spectrometry is a useful tool for studying in vivo kinetic changes in the oxygen saturation of haemoglobin and myoglobin as well as the redox state of cytochromes. A method is given which allows the quantification of tissue reflectance spectra using multicomponent analysis. This method utilizes the Kubelka-Munk theory for modelling the measured tissue spectra. To test this approach, reflectance spectra of a haemoglobin-free perfused guinea pig heart were measured by a fast scanning spectrophotometer (100 spectra/s, spectral resolution 1.0 nm) and evaluated using the component absorbance spectra measured separately. A relative mean spectral residual error of 0.15% was achieved by least-squares fitting. Using statistical error propagation, oxygenation of myoglobin is obtained within a relative precision of 1%, and the redox state of cytochromes aa3 and c are determined simultaneously within a margin of 3%; the results for the redox-state of cytochrome b, however, are less precise. Special component error functions are presented to provide a reliability measure for the concentration prediction using this multicomponent assay. The consistency of the theory and the component absorptivity data is tested by regressing the actual concentrations obtained for each of the redox pair components during the various states of tissue oxygenation. A method is described for the recognition and reduction of systematic errors.

Animals↗

PubMed1999

In vivo determination of the optical properties of muscle with time-resolved reflectance using a layered model.

We have investigated the possibility of determining the optical coefficients of muscle in the extremities with in vivo time-resolved reflectance measurements using a layered model. A solution of the diffusion equation for two layers was fitted to three-layered Monte Carlo calculations simulating the skin, the subcutaneous fat and the muscle. Relative time-resolved reflectance data at two distances were used to derive the optical coefficients of the layers. We found for skin and subcutaneous fat layer thicknesses (l2) of up to 10 mm that the estimated absorption coefficients of the second layer of the diffusion model have differences of less than 20% compared with those of the muscle layer of the Monte Carlo simulations if the thickness of the first layer of the diffusion model is also fitted. If l2 is known, the differences are less than 5%, whereas the use of a semi-infinite model delivers differences of up to 55%. Even if l2 is only approximately known the absorption coefficient of the muscle can be determined accurately. Experimentally, the time-resolved reflectance was measured on the forearms of volunteers at two distances from the incident beam by means of a streak camera. The thicknesses of the tissues involved were determined by ultrasound. The optical coefficients were derived from these measurements by applying the two-layered diffusion model, and results in accordance with the theoretical studies were observed.

Adipose Tissue↗

PubMed2003

The use of spatially resolved fluorescence and reflectance to determine interface depth in layered fluorophore distributions.

The possibility of using spatially resolved fluorescence and reflectance measurements to recover tissue optical properties, fluorophore concentration and the thickness of a superficial layer in a two-layer geometry was investigated. A diffusion theory model was used to fit reflectance and fluorescence data generated using Monte Carlo simulations or experimentally obtained using tissue-simulating phantoms. Initial analysis fitting diffusion theory generated data suggested that it should be possible to recover all parameters from a single set of spatially resolved fluorescence and reflectance measurements. However, when Monte Carlo or experimental data were fitted the results were less impressive. Overall, it was shown that there is a strong coupling between interface depth, fluorophore concentration and tissue absorption, especially at larger depths. The recovery of all input parameters from a single set of spatially resolved measurements was limited to interface depths less than 3 mm, which is a reasonable range for measuring fluorophore in skin. When the tissue optical properties and fluorophore concentrations were known, then the interface depth could be monitored with good accuracy in simulated serial measurements. These results may also point to deficiencies in the diffusion theory model that introduce significant errors in the fitted results.

Algorithms↗

PubMed2003

MRI quantification of the role of the reflected pressure wave on coronary and ascending aortic blood flow.

The respective roles of the windkessel effect, which is related to the vessel compliance, and of the returning pressure wave, which is reflected off peripheral resistances, in generating the total diastolic blood flow in the ascending aorta (VT: coronary + flow through the upper part of the ascending aorta) were assessed under physiological conditions. In ten healthy young men (21-30 years), magnetic resonance phase mapping was used to assess non-invasively both blood flow and vessel cross-sectional area (CSA) at the upper part of the ascending aorta. Measurements of blood flow velocities and CSAs were carried out over complete cardiac cycles, with a 30 ms resolution time. The total diastolic blood flow volume (VT) was significantly greater than the diastolic blood flow volume related to the windkessel effect (Vw). Consequently, since the windkessel effect could not account for the whole diastolic blood flow volume, the difference was attributed to the diastolic blood flow volume related to the reflected pressure wave (Vpw). The mean and SD of Vw and Vpw were estimated to be 4.34 +/- 1.94 ml/cycle and 6.80 +/- 2.40 ml/cycle (n = 10), respectively, for a measurement slice placed at 5.12 cm (on average) from the aortic valve and a mean coronary diastolic blood flow volume assumed to be equal to 4 ml/cardiac cycle in all subjects. The present non-invasive MR phase mapping study indicates that the windkessel effect and the reflected pressure wave might play a similar role in generating the total diastolic blood flow in the ascending aorta, under physiological conditions. Furthermore, pathophysiologic implications are discussed.

Adult↗