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At least 649 records · Page 36Linked to original sources

PubMed2000

Measuring Newtonian viscosity from the phase of reflected ultrasonic shear wave.

In this paper, an acoustic shear impedance model is employed to obtain a relation between the viscosity of a Newtonian fluid and phase characteristics of ultrasonic shear wave reflection from a solid-fluid interface. The phase and magnitude of the reflection coefficient can be decoupled in this model. The decoupling allows an independent relation between the acoustic shear impedance (viscosity-density product) and phase of the reflection coefficient. The model was experimentally verified for different fluid-solid combinations. Comparison of the results with the commonly used absolute reflection coefficient method demonstrates that phase measurement provides improved measurements.

Aluminum↗

PubMed2002

Multiple reflections of Lamb waves at a delamination.

Wave propagation in laminated plates with delaminations was calculated using the semi-analytical finite element method. The visualization results and deeper numerical analyses revealed the following phenomena on the fundamental Lamb modes at delamination regions of laminated plates. First, Lamb wave propagates toward the delamination, and then splits into two independent waves at the "Entrance" of the delamination with no significant reflections. These two waves reach the "Exit" of the delamination with the different phases and arrival time. Thus reflected and transmitted waves are excited at the Exit. The repetition of such reflections at the Exit causes the multiple reflections at regular intervals corresponding to the delamination size.

Journal Article↗

PubMed2001

Reflections of depression in acoustic measures of the patient's speech.

BACKGROUND: The literature on acoustic measures of voice in depression is reviewed. Authors have separated results derived from studies of automatic speech, such as counting or reading, from free speech. Free speech requires cognitive activity such as word finding and discourse planning in addition to the motor activity of automatic speech. Also, results have been less ambiguous if homogeneous groups of agitated or retarded depressed patients were examined. METHODS: These distinctions are applied to the results of a 12-week double-blind treatment trial that compared response to nortriptyline (25-100 mg/day) with sertraline (50-150 mg/day). Twelve male and ten female elderly depressed patients and an age-matched normal control group (n=19) were studied. Patients were divided into retarded or agitated groups on the basis of ratings. Results from measures of fluency (speech productivity and pausing) and prosody (emphasis and inflection) are described. RESULTS: Depressed patients showed less prosody than the normal subjects. Improvement in the retarded group was reflected in briefer pauses but not longer utterances. There was a trend in the agitated group for improvement to be reflected in the utterance but not the pause measure. CONCLUSIONS: Clinical impressions are substantially related to acoustic parameters. Temporal changes associated with depression appear to reflect the depressed state whereas prosodic features seem to reflect a depressed trait. Acoustic measures of the patient's speech may provide objective procedures to aid in the evaluation of depression. Limitations of the study are discussed.

Aged↗

PubMed1998

Reflection: a flawed strategy for the nursing profession.

The meaning and process of reflection and reflective practice appear to be currently accepted and institutionalized within the nursing profession. This paper, through use of a literature review, attempts to question the value that is consequently placed on this strategy and argues that on closer examination, reflection has no clear or universal definition, an uncertain framework for implementation, and is of unproven benefit to the professional practice of nurses. Given this evidence, the author concludes that reflection is a fundamentally flawed strategy that must be of limited benefit to the nursing profession.

Education, Nursing↗

PubMed2001

Pulmonary artery pulse pressure and wave reflection in chronic pulmonary thromboembolism and primary pulmonary hypertension.

OBJECTIVES: The purpose of this time-domain study was to compare pulmonary artery (PA) pulse pressure and wave reflection in chronic pulmonary thromboembolism (CPTE) and primary pulmonary hypertension (PPH). BACKGROUND: Pulmonary artery pressure waveform analysis provides a simple and accurate estimation of right ventricular afterload in the time-domain. Chronic pulmonary thromboembolism and PPH are both responsible for severe pulmonary hypertension. Chronic pulmonary thromboembolism and PPH predominantly involve proximal and distal arteries, respectively, and may lead to differences in PA pressure waveform. METHODS: High-fidelity PA pressure was recorded in 14 patients (7 men/7 women, 46 +/- 14 years) with CPTE (n = 7) and PPH (n = 7). We measured thermodilution cardiac output, mean PA pressure (MPAP), PA pulse pressure (PAPP = systolic - diastolic PAP) and normalized PAPP (nPAPP = PPAP/MPAP). Wave reflection was quantified by measuring Ti, that is, the time between pressure upstroke and the systolic inflection point (Pi), deltaP, that is, the systolic PAP minus Pi difference, and the augmentation index (deltaP/PPAP). RESULTS: At baseline, CPTE and PPH had similar cardiac index (2.4 +/- 0.4 vs. 2.5 +/- 0.5 l/min/m2), mean PAP (59 +/- 9 vs. 59 +/- 10 mm Hg), PPAP (57 +/- 13 vs. 53 +/- 13 mm Hg) and nPPAP (0.97 +/- 0.16 vs. 0.89 +/- 0.13). Chronic pulmonary thromboembolism had shorter Ti (90 +/- 17 vs. 126 +/- 16 ms, p < 0.01) and higher deltaP/PPAP (0.26 +/- 0.01 vs. 0.09 +/- 0.07, p < 0.01). CONCLUSIONS: Our study indicated that: 1) CPTE and PPH with severe pulmonary hypertension had similar PA pulse pressure, and 2) wave reflection is elevated in both groups, and CPTE had increased and anticipated wave reflection as compared with PPH, thus suggesting differences in the pulsatile component of right ventricular afterload.

Adult↗

PubMed1999

Nurses' self-reflection via videotaping to improve communication skills in health counseling.

The purpose of this qualitative research was to describe nurses' opinions of their communication skills in health counseling situations and to analyze the levels of reflectivity in their evaluations according to Mezirow. Nineteen nurses participated in the research on a voluntary basis and evaluated their interaction with patients on video on two occasions half a year apart. Nurses gave verbal feedback in an interview immediately after videotaping, after which they read education materials, watched their counseling on video and wrote an evaluation of their communication skills. Transcribed audiotaped interviews and written evaluations were analyzed using content analysis. Nurses said that they were able to use familiar language, to listen and to encourage patients to express their feelings and ask questions. Nurses gave little feedback on nonverbal communication. They wanted to develop their listening skills and their ability to encourage patients to ask and express their feelings. They also wanted to improve their preparations for counseling sessions. On Mezirow's scale, nurses' evaluations weighted heavily towards the lower levels of reflectivity. Only one nurse's evaluations were on the sixth level and no evaluations were on the seventh level. The results indicated a need for training programs dealig with communication skills and self-reflection. Using the videotape and self-reflection were found to be good methods to enhance the quality of health counseling.

Adolescent↗

PubMed2002

Amplitude and timing of central aortic pressure wave reflections in heart transplant recipients.

BACKGROUND: Hypertension (HTN) assessed by sphygmomanometer is a common finding in heart transplant recipients (HTR); however, little is known about the contribution of arterial wave reflection to central aortic pressure in these patients. The aim of this study was to measure the central aortic pressure wave in HTR on antihypertensive therapy and determine the effects of amplitude and timing of wave reflection on the various components of the wave. METHODS: A total of 53 stable adult HTR on antihypertensive medication underwent brachial artery blood pressure ([BP]; by sphygmomanometry) and central aortic pressure (by noninvasive radial artery applanation tonometry and use of a generalized transfer function) measurements at rest. Central aortic augmentation index (Ala), an indicator of arterial stiffness, was calculated from the aortic pressure waveform. Patients were divided into three groups (A, B, and C) based on the amplitude of AIa. RESULTS: Mean brachial BP was 136 +/- 15/84 +/- 9.4 mm Hg. Group A patients (n = 25) had a higher AIa (average 21% +/- 7.6%) than group B (n = 18, AIa = 6.5% +/- 3.0%, P < .001) or group C (n = 10, AIa = -8.7% +/- 8.1%, P < .001) patients. The amplitude of AIa was inversely related to the travel time (delta(t)p/2) of the reflected pressure wave from the periphery to the heart (r = -0.78, P < .001). Despite this clear stratification of patients by aortic pulse wave analysis, standard cuff pressure was similar among the groups. CONCLUSIONS: Noninvasive analysis of the central aortic PRESSURE wave identified a subgroup of hypertensive HTR with increased arterial stiffness, increased propagation of the reflected wave, and augmented aortic systolic and pulse pressure not identified with the sphygmomanometer.

Adult↗

PubMed2003

About forbidden and weak reflections.

Reflections forbidden under the single scattering approximation are not expected to remain extinct for crystal thicknesses for which multiple scattering becomes important, except for reflections of the Gjönnes-Moodie type. However, it has been observed that in many crystals with the incident beam along a zone axis, such as diamond-like crystals along the [110] zone, reflections forbidden under the single scattering approximation remain very weak up to large thicknesses. This is hard to explain in terms of many-beam dynamical scattering in Fourier space. The picture becomes clear if one describes the scattering in real space in terms of the channelling of the electrons along the atom columns parallel to the zone axis. In that case the exit wave of each atom column can be described by the S-state model, which is radially symmetric around the centre of the atom column. As a consequence the exit wave shows the same symmetry as the projected potential, so that the reflections forbidden under the single scattering approximation remain extinct. This condition only breaks down when the crystal thickness becomes so large that the S-state model becomes invalid, which is a function of the distance between neighbouring atom columns and/or the tilt from the exact zone axis. The sensitivity for small tilts is also in agreement with very old observations that have not been explained thus far.

Journal Article↗

PubMed1997

UV induced erythema evaluated 24 h post-exposure by skin reflectance and laser Doppler flowmetry is identical in healthy persons and patients with cutaneous malignant melanoma and basal cell cancer.

Twenty-one patients with invasive cutaneous malignant melanoma and 19 patients with basal cell skin cancer and 29 healthy volunteers were phototested on non-UV exposed buttock skin to examine their 24 h reaction to a series of increasing doses of simulated sunlight with 25% dose increments. Skin pigmentation at the phototest sites was determined by skin reflectance before testing to assure an equal level of constitutive skin pigmentation in the 3 groups. Erythema reactions were scored visually 24 hours post-exposure and objective measurements of erythema were performed by skin reflectance and laser Doppler flowmetry. In adjacent non-irradiated skin the redness was also quantified to determine the increase in redness in irradiated skin compared to non-irradiated skin. Constitutional skin pigmentation correlated well to UV sensitivity (r = 0.75) and skin redness measured by skin reflectance technique correlated to laser Doppler flowmetry (r = 0.86). No significant differences in UV doses to barely perceptible erythema or to the higher erythema grades were found between the two skin tumour groups and the control group, and no significant differences were found in skin reflectance measured redness or in laser Doppler flowmetry of any erythema reactions between the 3 groups. The 24 h erythema reaction to sunlight can therefore not be used to distinguish patients with invasive cutaneous malignant melanoma or basal cell carcinoma from normal persons.

Erythema↗

PubMed1996

Measurement of blood flow with radiolabeled microspheres in reflected mucogingival flaps in cats.

To quantify and compare blood flow in maxillary mucogingival flaps, a total of 16 cats (32 mucogingival specimens) were divided into two groups. In group I the blood flow in attached or reflected maxillary tissues were measured. In Group II the effects on blood flow were measured in reflected tissues after the injection of the following solutions: (1) saline solution; (2) 2% lidocaine plain; (3) 2% lidocaine with 1:50,000 epinephrine; (4) no injection. After an injection of 153 Gadolinium microspheres into the left ventricle of the heart, the tissues were harvested and placed in a gamma counter. Group I had a mean blood flow value of 34.4 ml/min/100 gm of tissue for the unreflected samples and 152.3 ml/min/100 gm of reflected tissue. The levels of blood flow in tissue samples in group II results were: no injection (control), 41.2 ml/min/100 gm; saline solution, 46.8 ml/min/110 gm; 2% lidocaine with 1:50,000 epinephrine, 60.6 ml/min/100 gm; and 2% lidocaine plain, 90.2 ml/min/100 gm. On the basis of these results it appears that reflection of gingival tissue and injection of 2% lidocaine plain induces increased blood flow 90 minutes postoperatively.

Adrenergic beta-Agonists↗

PubMed1999

Reflective topical autobiography: an under utilised interpretive research method in nursing.

Reflective topical autobiography (an autobiographical method) belongs to the genre of testimonial research and is located within the postpositivist interpretive research paradigm. Despite the (reflective) topical autobiographical method enjoying a 'rebirth' in recent years and being utilised by a range of researchers in the human and literary disciplines, it remains largely unknown and under utilised in nursing research domains. In this article it is proposed that reflective topical autobiography is an important research method in its own right, and one which promises to make a substantive contribution to the overall project of advancing nursing inquiry and knowledge. This is particularly so where nursing research shares in the affirming projects of interpretive research generally and the relatively new sociology of the emotions in particular apropos: (i) increasing understanding of subjectivity and making subjective experiences more visible and intelligible, (ii) the search for meaning and increasing understanding of the commonality of existential human experience, and (iii) decentring the detached observer and his/her privileging the objectivist illusion in the hierarchy of research discourses, paving the way for the admission of multiple realities and interpretations of lived experience. In this article, a coherent reflective topical autobiographical research method is advanced for use in nursing education and research contexts.

Autobiographies as Topic↗

PubMed2003

Effect of protein and temperature on cutting time prediction in goats' milk using an optical reflectance sensor.

An objective method for determining the coagulum cutting time is needed to improve consistency and processing efficiency of goats' cheese. A fibre optic sensor was used to measure the backscatter of near-infrared radiation at 880 nm during the coagulation of skimmed goats' milk for the purpose of predicting coagulum cutting time. A randomised block design, replicated three times, was used to test the effect of three protein concentrations (3, 5 and 7% (w/w)) on diffuse reflectance parameters for cutting time prediction of milk coagulated at five different temperatures (20, 25, 30, 35 and 40 degrees C) to assure a wide range of coagulation rates. The inclusion of a protein term in the existing algorithms was essential to reduce the standard error of prediction to under 6.2 min. An algorithm including a time-based parameter and a protein term, Tcut=beta0 T2min (1 + gamma% Protein) was found to predict cutting time with a SEP of 2.42 min and an R2 of 0.98. Gamma was considered constant (gamma=-0.0674, goats' milk) representing the protein effect on beta0. Algorithms using response-based parameters (such as change in reflectance ratio) and the composition parameter protein required additional regression parameters such as temperature and an intercept term to predict the cutting time with the same precision as algorithms using only time-based parameters. Time-based parameters were found to decrease proportionally with increasing temperature and decreasing protein concentration. Response-based and mixed-based parameters were found to decrease with decreasing temperature. Reflectance ratio at cutting time did not significantly change with protein concentration for skimmed goats' milk. The activation energy of kappa-casein hydrolysis was calculated based on changes in reflectance profile parameters and was found to be in the range 63-72 kJ mol(-1).

Algorithms↗

PubMedDate not supplied

Protanopic observers show nearly normal color constancy with natural reflectance spectra.

The ability of color-deficient observers to discriminate between illuminant changes and surface-reflectance changes in a scene was tested with natural and Munsell reflectance spectra. To avoid the confounding effects of spatial structure, stimuli were simulations of Mondrian-like colored patterns, presented on a computer-controlled color monitor. Protanopes performed less well than normal trichromats, regardless of the type of reflectance spectra, but they were least disadvantaged with patterns comprising reflectance spectra drawn from urban and rural scenes, more characteristic of the natural environment.

Adult↗

PubMed2001

Hydrodynamic potential-modulated reflectance spectroscopy: theory and experiment.

This article describes the development and application of a new electrochemical methodology based on potential-modulated UV-vis reflectance spectroscopy (PMRS). The device configuration is based upon a thin-layer flow-through channel cell incorporating a platinum working electrode. Reagent solutions are pumped through the cell under well-defined hydrodynamic conditions and electrolyzed at the platinum working electrode. Measurements are presented for linear sweep and fixed dc potentials with a superimposed small amplitude sinusoidal potential perturbation. A UV-vis source is employed to irradiate the electrode region, and the resulting reflected signal is analyzed using a phase sensitive detector. Experimental studies using tris(4-bromophenyl) amine (TBPA) in acetonitrile are presented which quantify the relationship between the absorption spectrum and reflected light intensity as a function of the transport rate, electrolysis reactions, and the modulation frequency of the incident irradiation. The experimental results are analyzed using numerical simulations based on a finite difference strategy. These permit the quantitative prediction of the concentration distribution of reagents within the cell. A fast Fourier transform (FFT) routine was used to analyze the frequency response of the numerically predicted reflectance signal. Excellent agreement was observed between the numerical predictions and experimental observations.

Journal Article↗

PubMed2006

Improving the linearity of infrared diffuse reflection spectroscopy data for quantitative analysis: an application in quantifying organophosphorus contamination in soil.

Diffuse reflection data are presented for ethyl methylphosphonate in a fine Utah dirt sample as a model system for organophosphate-contaminated soil. The data revealed a chemometric artifact when the spectra were represented in Kubelka-Munk units that manifests as a linear dependence of spectral peak height on variations in the observed baseline position (i.e., the position of the observed transmission intensity where no absorption features occur in the sample spectrum). We believe that this artifact is the result of the mathematical process by which the raw data are converted into Kubelka-Munk units, and we developed a numerical strategy for compensating for the observed effect and restoring chemometric precision to the diffuse reflection data for quantitative analysis while retaining the benefits of linear calibration afforded by the Kubelka-Munk approach. We validated our Kubelka-Munk correction strategy by repeating the experiment using a simpler system--pure caffeine in potassium bromide. The numerical preprocessing includes conventional multiplicative scatter correction coupled with a baseline offset correction that facilitates the use of quantitative diffuse reflection data in the Kubelka-Munk formalism for the quantitation of contaminants in a complex soil matrix, but is also applicable to more fundamental diffuse reflection quantitative analysis experiments.

Linear Models↗

PubMed2004

Equivalence of elemental carbon by thermal/optical reflectance and transmittance with different temperature protocols.

Charring of organic carbon (OC) during thermal/optical analysis is monitored by the change in a laser signal either reflected from or transmitted through a filter punch. Elemental carbon (EC) in suspended particulate matter collected on quartz-fiber filters is defined as the carbon that evolves after the detected optical signal attains the value it had prior to commencement of heating, with the rest of the carbon classified as organic carbon (OC). Heretofore, operational definitions of EC were believed to be caused by different temperature protocols rather than by the method of monitoring charring. This work demonstrates that thermal/ optical reflectance (TOR) corrections yield equivalent OC/ EC splits for widely divergent temperature protocols. EC results determined by simultaneous thermal/optical transmittance (TOT) corrections are 30% lower than TOR for the same temperature protocol and 70-80% lower than TOR for a protocol with higher heating temperatures and shorter residence times. This is true for 58 urban samples from Fresno, CA, as well as for 30 samples from the nonurban IMPROVE network that are individually dominated by wildfire, vehicle exhaust, secondary organic aerosol, and calcium carbonate contributions. Visual examination of filter darkening at different temperature stages shows that substantial charring takes place within the filter, possibly due to adsorbed organic gases or diffusion of vaporized particles. The filter transmittance is more influenced by the within-filter char, whereas the filter reflectance is dominated by charring of the near-surface deposit that appears to evolve first when oxygen is added to helium in the analysis atmosphere for these samples. The amounts of charred OC (POC) and EC are also estimated from incremental absorbance. Small amounts of POC are found to dominate the incremental absorbance. EC estimated from absorbance are found to agree better with EC from the reflectance charring correction than with EC from the transmittance charring correction.

Adsorption↗

PubMed2005

Feasibility of reflectance spectroscopy for the assessment of soil mercury contamination.

Conventional methods for investigating soil Hg contamination based on raster sampling and chemical analysis are time-consuming and relatively expensive. The objective of this study was to develop a rapid method for investigating Hg concentration in suburban agricultural soils of the Nanjing region using reflectance spectra within the visible-near-infrared (VNIR) region. Several spectral pretreatments (absorbance, Kubelka-Munk transformations and their derivatives) were applied to the reflectance spectra to optimize the accuracy of prediction. The prediction of Hg concentration was achieved by univariate regression and principal component regression (PCR) approaches. The optimal model (R= 0.69, RMSEP = 0.15) for predicting Hg was achieved using the PCR method with the Kubelka-Munktransformation asthe spectral predictor. Comparison of three wavelength ranges (0.38-1.1, 1.0-2.5, and 0.38-2.5 microm) on the effect of prediction accuracy showed that the best results were acquired using the 1.0-2.5 microm spectral region. Correlation analysis revealed that Hg concentration was negatively correlated with soil reflectance while positively correlated with the absorption depths of goethite at 0.496 microm and clay minerals at 2.21 microm, suggesting that Hg-sorption by clay-size mineral assemblages in soils was the mechanism by which to predict spectrally featureless Hg. These results indicate that it is feasible to predict Hg levels in agricultural soils using the rapid and cost-effective reflectance spectroscopy. Future study with operational remote sensing techniques and field measurements is strongly recommended.

Absorption↗

PubMed2003

Adsorption of beta-hairpin peptides on the surface of water: a neutron reflection study.

Neutron reflectivity has been used to determine the thickness and surface coverage of monolayers of two 14-residue beta-hairpin peptides adsorbed at the air/water interface. The peptides differed only in that one was labeled with a fluorophore, while the other was not. The neutron reflection measurements were mainly made in null reflecting water, NRW, containing 8.1% D(2)O. Under this isotopic contrast the water is invisible to neutrons and the specular signal was then only from the peptide layer. At the highest concentration of ca. 4 microg/mL studied, the area per peptide molecule (A) was found to be 230 +/- 10 and 210 +/- 10 A(2) for the peptides with and without a BODIPY-based fluorophore, respectively. The thickness of the peptide layers was about 10 A for a Gaussian distribution. With decreasing bulk peptide concentration, both surface excess and layer thickness showed a steady trend of decrease. While the neutron results clearly indicate structural changes within the peptide monolayers with increasing bulk concentration, the outstanding structural feature is the formation of rather uniform peptide layers, consistent with the structural characteristics typical of beta-strand peptide conformations. These structural features are well supported by the parallel measurements of the adsorbed layers in D(2)O. With this isotopic contrast the neutron reflectivity provides an estimate about the extent of immersion of the peptide layers into water. The results strongly suggest that the 14-mer peptide monolayers were fully afloat on the surface of water, with only the carboxy groups on Glu residues hydrated.

Adsorption↗