Experimental and theoretical investigation of the Leidenfrost dynamics of solid carbon dioxide discs sublimating on a solid substrate

Volatile liquid droplets levitate on a cushion of their vapor when placed on a hot solid substrate. While extensive research has focused on investigating this phenomenon, commonly known as the Leidenfrost effect in the context of liquids, it may also occur for solids whose triple point pressure is above normal ambient conditions. The present study experimentally and theoretically investigates the Leidenfrost effect for a disc-shaped dry ice pellet placed on a temperature-controlled hot sapphire substrate. The spatial and temporal evolution of the vapor layer thickness below the pellet is measured for varying substrate temperatures using optical coherence tomography (OCT). Simultaneously, the shrinkage of the sublimating dry ice pellet is recorded using video cameras. It is shown that the bottom surface of the pellet is approximately flat within the surface roughness and the resolution of the experimental setup. Intriguingly, this study reveals that the vapor layer thickness below a Leidenfrost solid increases with time in contrast to the dynamics observed for a Leidenfrost liquid droplet/puddle. Additionally, a theoretical model based on the lubrication approximation is employed to estimate the vapor layer thickness and the temporal evolution of the pellet's geometry. The theoretical predictions generally agree well with the measurements throughout the majority of the pellet's lifespan, with deviations observed towards the end of its sublimation due to the assumption of a constant pellet diameter in the model. Furthermore, the theoretical predictions reasonably represent the pellet's lifetime across a wide range of substrate temperatures, validating the predictive capabilities of the theoretical model in the present scenario.</p

Limitations and opportunities of whole blood bilirubin measurements by GEM premier 4000®

Abstract Background Neonatal hyperbilirubinemia has traditionally been screened by either total serum bilirubin or transcutaneous bilirubin. Whole blood bilirubin (TwB) by the GEM Premier 4000® blood gas analyzer (GEM) is a relatively new technology and it provides fast bilirubin results with a small sample volume and can measure co-oximetry and other analytes. Our clinical study was to evaluate the reliability of TwB measured by the GEM and identify analytical and clinical factors that may contribute to possible bias. Methods 440 consecutive healthy newborn samples that had plasma bilirubin ordered for neonatal hyperbilirubinemia screening were included. TwB was first measured using the GEM, after which the remainder of the blood was spun and plasma neonatal bilirubin was measured using the VITROS 5600® (VITROS). Results 62 samples (14%) were excluded from analysis due to failure in obtaining GEM results. Passing-Bablok regression suggested that the GEM results were negatively biased at low concentrations of bilirubin and positively biased at higher concentrations relative to the VITROS results (y = 1.43x-61.13). Bland-Altman plots showed an overall negative bias of the GEM bilirubin with a wide range of differences compared to VITROS. Both hemoglobin concentration and hemolysis affected the accuracy of the GEM results. Clinically, male infants had higher mean bilirubin levels, and infants delivered by caesarean section had lower hemoglobin levels. When comparing the number of results below the 40th percentile and above the 95th percentile cut-offs in the Bhutani nomogram which would trigger discharge or treatment, GEM bilirubin exhibited poor sensitivity and poor specificity in contrast to VITROS bilirubin. Conclusions An imperfect correlation was observed between whole blood bilirubin measured on the GEM4000® and plasma bilirubin on the VITROS 5600®. The contributors to the observed differences between the two instruments were specimen hemolysis and the accuracy of hemoglobin measurements, the latter of which affects the calculation of plasma-equivalent bilirubin. Additionally, the lack of standardization of total bilirubin calibration particularly in newborn specimens, may also account for some of the disagreement in results

Quantitative and localized spectroscopy for non-invasive bilirubinometry in neonates

Couveusekinderen lopen een verhoogd risico op geelzucht, wat kan leiden tot hersenschade. Kinderen met geelzucht krijgen meerdere hielprikken per dag om de bilirubinewaarde in het bloed te bepalen. Bilirubine is het afbraakproduct van hemoglobine, dat kan zorgen voor een gelige huidskleur. Een mogelijk alternatief voor deze pijnlijke methode is optische spectroscopie, een niet-invasieve techniek die gebaseerd is op de absorptie van licht door bilirubine in de huid. Voor dit doel zijn al sinds 1980 bilirubinemeters ontwikkeld, maar de pijnlijke hielprik is nog niet vervangen. Nienke Bosschaart onderzocht de oorzaken hiervan en keek naar mogelijke verbeteringen. Veelbelovend is een nieuwe vorm van spectroscopie (LCS: laag-coherente spectroscopie), waarmee van buitenaf de bilirubinewaarde in één enkel bloedvat in de huid kan worden bepaald

In vivo low-coherence spectroscopic measurements of local hemoglobin absorption spectra in human skin

Localized spectroscopic measurements of optical properties are invaluable for diagnostic applications that involve layered tissue structures, but conventional spectroscopic techniques lack exact control over the size and depth of the probed tissue volume. We show that low-coherence spectroscopy (LCS) overcomes these limitations by measuring local attenuation and absorption coefficient spectra in layered phantoms. In addition, we demonstrate the first in vivo LCS measurements of the human epidermis and dermis only. From the measured absorption in two distinct regions of the dermal microcirculation, we determine total hemoglobin concentration (3.0 +/- 0.5 g/l and 7.8 +/- 1.2 g/l) and oxygen saturation. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3644497