James B. Callis

Luminescent barometry in wind tunnels

A flexible and relatively inexpensive method and apparatus are described for continuous pressure mapping of aerodynamic surfaces using photoluminescence and imaging techniques. Platinum octaethylporphyrin (PtOEP) has a phosphorescence known to be quenched by oxygen. When dissolved in a silicone matrix, PtOEP may be distributed over a surface as a thin, uniform film. When the film is irradiated with ultraviolet light, the luminescence intensity provides a readily detectable, qualitative surface flow visualization. Moreover, since the luminescence intensity is found to be inversely proportional to the partial pressure of oxygen, a quantitative measure of pressure change may be obtained using a silicon target vidicon or a charge‐coupled device video sensor to measure intensity. Luminescent images are captured by a commercial frame buffer board. Images taken in wind tunnels during airflow are ratioed to images taken under ambient ‘‘wind‐off’’ conditions. The resulting intensity ratio information is converted ...

CALORIMETRIC, PHOTOMETRIC AND LIFETIME DETERMINATIONS OF FLUORESCENCE YIELDS OF FLUORESCEIN DYES*

Abstract— The fluorescence yields and lifetimes of fluorescein and nine brominated derivatives in basic ethanol are reported. Calorimetric. photometric, and lifetime methods are used independently to measure the yields. A new and simple calorimetric method is presented for this purpose, and the accuracy of the techniques is assessed. There is good agreement between the calorimetric and photometric results. The importance of parameters such as purity, pH, and fluoresence reabsorption is illustrated. The theoretical determination of the natural radiative lifetime from the absorption spectrum is shown to have inherent ambiguities, so that only calorimetric methods provide a reliable, independent check for photometric yield measurements.

Submillisecond response times of oxygen‐quenched luminescent coatings

An apparatus and data analysis methodology is described which allows determination of response time to oxygen concentration changes of luminescent oxygen sensor coatings. Utilizing a solenoid valve, a sample chamber creates a pressure jump from 0.1 to 700 Torr in 600 μs that is followed by 15 ms of ringing. An optical detection system measures the response of porphyrin‐based luminescent oxygen sensors to the pressure jump. The pressure in the chamber is measured simultaneously and independently with a piezoresistive pressure transducer. Data analysis techniques using nonlinear least‐squares and numerical convolution of the luminescent response to the pressure rise allow determination of response times of the oxygen sensor. The response to pressure jumps of several luminescent oxygen sensitive coatings designed for video luminescent barometry are measured with this computer‐controlled instrument. Several coatings were studied with response times of ∼2.5 s, ∼400 ms, 11 ms, 1.5 ms, and <25 μs. Studies of the...

Europium beta-diketonate temperature sensors: Effects of ligands, matrix, and concentration

Europium beta diketonates are easily synthesized highly luminescent complexes with high temperature sensitivity. We report on the temperature dependence of the luminescence of recently synthesized europium complexes originally prepared for use as light emitting diodes. It has been discovered that when incorporated in a polymer matrix, their decay lifetime can provide accurate measurement of temperature. Their lifetime as a function of temperature depends on three factors: (i) the type and number of ligands in the complex, (ii) the particular polymer used for the matrix, and (iii) the europium chelate to polymer matrix concentration ratio. Various tris and tetrakis europium chelates are used to study ligand effects, while the polymers FIB, polycarbonate, and Teflon© are used to analyze matrix effects. In all cases studied, higher concentrations give rise to shorter lifetimes and higher temperature sensitivities, with sensitivity defined as ΔI/(IrefΔT). We propose to explain this phenomenon by using the fol...

Multispectral imaging of burn wounds: a new clinical instrument for evaluating burn depth

A real-time video imaging system called the imaging burn depth indicator (IBDI) is described; IBDI can discriminate areas of burn wounds expected to heal in three weeks or less from the day of injury from those areas not expected to heal in that time period. The analysis can be performed on or about the third day postburn on debrided burn wounds. The relative diffuse reflectivity of the burn-wound is measured in the red, green, and near-infrared wavelength bands and an algorithm established previously is used to translate this optical data into burn healing probabilities. Over 100 burn wound sites were studied. Burn sites were evaluated on day three postburn by the IBDI and by the attending physician. Overall, the IBDI was found to be more accurate in predicting burn healing than were the attending physicians.<<ETX>>

Dual-luminophor pressure-sensitive paint: I. Ratio of reference to sensor giving a small temperature dependency

Pressure-sensitive paint (PSP) is playing an important role in aerodynamic testing. Its use provides a number of advantages over discrete pressure taps traditionally used on conventional wind tunnel models: (i) obtaining continuous quantitative pressure distributions over a surface; (ii) visualizing dynamic flow processes that measure areas not possible with conventional pressure taps (e.g. thin trailing edges); and (iii) real time modeling. The result is better integration of experimental and computational fluid dynamics leading to significant reductions in time for prototyping of new designs. The use of PSP relies on accurate measurement of changes in the paint’s luminescent intensity as a function of pressure change, which in turn requires careful monitoring and placement of light sources and pre-calibration of the PSP covered surface in “wind-off” conditions. Paint in-homogeneity and inconsistent surface illumination require exact registration of the calibration ‘wind-off’ image with subsequent ‘wind-on’ images for intensity change calculations to be meaningful. Model motion between ‘wind-on’ and ‘wind-off’ images leads to systematic errors that are hard to quantify. A dual-luminophor paint containing both a sensor and a reference luminophor molecule should alleviate these technical problems. This paper introduces such a dual-luminophor PSP made from our newly developed oxygen-sensitive molecule platinum tetra(pentafluorophenyl)porpholactone (PtTFPL), which provides Isen, and magnesium tetra(pentafluorophenyl)porphine (MgTFPP), which provides Iref as the pressure-independent reference. The ratio Iref /Isen in the FIB polymer produced ideal PSP measurements with a temperature dependency of −0.1%/ ◦ C.

Surface pressure field mapping using luminescent coatings

In recent experiments we demonstrated the feasibility of using the oxygen dependence of luminescent molecules for surface pressure measurement in aerodynamic testing. This technique is based on the observation that for many luminescent molecules the light emitted increases as the oxygen partial pressure, and thus the air pressure, the molecules see decreases. In practice the surface to be observed is coated with an oxygen permeable polymer containing a luminescent molecule and illuminated with ultraviolet radiation. The airflow induced surface pressure field is seen as a luminescence intensity distribution which can be measured using quantitative video techniques. Computer processing converts the video data into a map of the surface pressure field. The experiments consisted of evaluating a trial luminescent coating in measuring the static surface pressure field over a two-dimensional NACA-0012 section model airfoil for Mach numbers ranging from 0.3 and 0.66. Comparison of the luminescent coating derived pressures were made to those obtained from conventional pressure taps. The method along with the experiment and its results will be described.

Fast changes of enthalpy and volume on flash excitation of Chromatium chromatophores

We have used a capacitor microphone transducer to measure volume changes in suspensions of Chromatium chromatophores 100 μs to 20 ms after flash excitation. Volume changes in photochemical reactions can arise both from volume differences between reactants and products, and from enthalpy changes which heat or cool the solution. By measuring the volume changes at two temperatures, one can resolve the total changes into their two components. In Chromatium, light-driven electron transfer from cytochrome C555 to the primary or secondary electron acceptors causes a contraction of approx. 33 A3 per electron transferred. The relaxation of the initial volume change is altered by the presence of gramicidin, valinomycin, o-phenanthroline, or phosphate. From the effects of these agents, we conclude that the volume change is localized at the photochemical reaction center, and that part of the relaxation involves transfer of a proton from the solvent to the chromatophores. Electron transfer from cytochrome C555 to the primary or secondary electron acceptors does not cause a significant enthalpy change. We conclude that the free energy increase that accompanies this reaction is due to a negative entropy change.

Continuous measurement of oxygen consumption by pancreatic islets.

The rate of oxygen consumption is an important measure of mitochondrial function in all aerobic cells. In pancreatic beta cells, it is linked to the transduction mechanism that mediates glucose-stimulated insulin secretion. However, measurement of oxygen consumption over long periods of time is technically difficult owing to the error resulting from baseline drift and the challenge of measuring small changes in oxygen tension. We have adapted an ultrastable oxygen sensor based on the detection of the decay of the phosphorescent emission from an oxygen-sensitive dye to a previously developed islet flow culture system. The drift of the sensor is approximately 0.3%/24 h, allowing for the continuous measurement of oxygen consumption by 300 islets (or about 6 x 10(5) cells) for hours or days. Rat islets placed in the perifusion chamber for 24 h were well maintained as reflected by membrane integrity, insulin secretion, and oxygen consumption. Both acute changes in oxygen consumption as induced by glucose and chronic changes as induced by sequential pulses of azide were resolved. The features of the flow culture system--aseptic conditions, fine temporal control of the composition of the media, and the collection of outflow fractions for measurement of insulin, and other products--facilitate a systematic approach to assessing metabolic and functional viability in responses to a variety of stimuli. Applications to the measurement of effects of hypoxia on insulin secretion, membrane integrity, and the redox state of cytochromes are demonstrated. The system has particular application to the field of human islet transplantation, where assessment and the study of islet viability have been hampered by a lack of experimental methods.

Chemical Sensing in Process Analysis

Improvements in process control, which determine production efficiency and product quality, are critically dependent upon on-line process analysis. The technology of the required instrumentation will be substantially expanded by advances in sensing devices. In the future, the hardware will consist of sensor arrays and miniaturized instruments fabricated by microlithography and silicon micromachining. Chemometrics will be extensively used in software to provide error detection, selfcalibration, and correction as well as multivariate data analysis for the determination of anticipated and unanticipated species. A number of examples of monolithically fabricated sensors now exist and more will be forthcoming as the new paradigms and new tools are widely adopted. A trend toward not only on-line but even in-product sensors is becoming discernible.