Dew-point hygrometry system for measurement of evaporative water loss in infants

Ariagno, Ronald L., Steven F. Glotzbach, Roger B. Baldwin,David M. Rector, Susan M. Bowley, and Robert J. Moffat.Dew-point hygrometry system for measurement of evaporative waterloss in infants. J. Appl. Physiol.82(3): 1008-1017, 1997.Evaporation of water from the skin is animportant mechanism in thermal homeostasis. Resistance hygrometry, inwhich the water vapor pressure gradient above the skin surface iscalculated, has been the measurement method of choice in the majorityof pediatric investigations. However, resistance hygrometry isinfluenced by changes in ambient conditions such as relative humidity,surface temperature, and convection currents. We have developed aventilated capsule method that minimized these potential sources ofmeasurement error and that allowed second-by-second, long-term,continuous measurements of evaporative water loss in sleeping infants.Air with a controlled reference humidity (dew-point temperature = 0°C) is delivered to a small, lightweight skin capsule and mixedwith the vapor on the surface of the skin. The dew point of theresulting mixture is measured by using a chilled mirror dew-pointhygrometer. The system indicates leaks, is mobile, and is accuratewithin 2%, as determined by gravimetric calibration. Examples from arecording of a 13-wk-old full-term infant obtained by using the systemgive evaporative water loss rates of ~0.02mgH₂O ^· cm^{2 ·} min¹for normothermic baseline conditions and values up to 0.4 mgH₂O ^· cm^{2 ·}min¹ when the subject wasbeing warmed. The system is effective for clinical investigations thatrequire dynamic measurements of water loss.

     

New techniques in fast time-resolved structure determination.

New techniques in fast time-resolved X-ray crystallography provide a different approach to understanding the structural basis of protein function. Two biological systems have been studied as part of the refinement of these techniques, and have actually spurred new ideas in time-resolved structural studies. The dissociation of carbon monoxide from carbon-monoxy myoglobin has earlier been investigated over a time range spanning 18 orders of magnitude (femtoseconds to hours) using spectroscopic methods. Rapid time-resolved determination of the entire myoglobin structure made it possible to determine both the position of the CO after photodissociation and the entire globin structure, over a time range from nanoseconds to milliseconds, during which the heme and globin relax and the carbon monoxide rebinds. Photoactive yellow protein, a relative newcomer to biophysical research, has a fully-reversible photocycle containing several spectrally distinct intermediates. Identifying and solving the structures of each intermediate is the initial goal in time-resolved studies on this protein and will contribute to a greater understanding of the biological process of light driven signal transduction.     

Extended X-ray absorption fine structure studies of Zn2Fe2 hybrid hemoglobins: absence of heme bond length changes in half-ligated species

Metal hybrid hemoglobins, in which Zn(II) replaces Fe(II), have been structurally characterized by extended X-ray absorption structure (EXAFS) studies. Since Zn and Fe have very different K absorption edge energies, the structures of the ligated (Fe) and unligated (Zn) sites could be examined independently within a single molecule that mimics an intermediate ligation state. The observed EXAFS spectra and associated structural parameters are compared among the ligand free (alpha Zn)2(beta Zn)2, half-ligated (alpha FeCO)2(beta Zn)2 and (alpha Zn)2(beta FeCO)2, and fully ligated (alpha FeCO)2(beta FeCO)2 systems.     

Evolution of three Pyrenophora cereal pathogens: Recent divergence, speciation and evolution of non-coding DNA

Three of the most important fungal pathogens of cereals are Pyrenophora tritici-repentis, the cause of tan spot on wheat, and Pyrenophora teres f. teres and Pyrenophora teres f. maculata, the cause of spot form and net form of net blotch on barley, respectively. Orthologous intergenic regions were used to examine the genetic relationships and divergence times between these pathogens. Mean divergence times were calculated at 519kya (±30) between P. teresf. teres and P. teresf. maculata, while P. tritici-repentis diverged from both Pyrenophora teresforms 8.04Mya (±138ky). Individual intergenic regions showed a consistent pattern of co-divergence of the P. teresforms from P. tritici-repentis, with the pattern supported by phylogenetic analysis of conserved genes. Differences in calculated divergence times between individual intergenic regions suggested that they are not entirely under neutral selection, a phenomenon shared with higher Eukaryotes. P. tritici-repentis regions varied in divergence time approximately 5-12Mya from the P. teres lineage, compared to the separation of wheat and barley some 12Mya, while the P. teresf. teres and P. teresf. maculata intergenic region divergences correspond to the middle Pleistocene. The data suggest there is no correlation between the divergence of these pathogens the domestication of wheat and barley, and show P. teresf. teres and P. teresf. maculata are closely related but autonomous. The results are discussed in the context of speciation and the evolution of intergenic regions.     

Thermoregulation and the determinants of heat transfer in Colias butterflies

Summary As a means of exploring behavioral and morphological adaptations for thermoregulation in Colias butterflies, convective heat transfer coefficients of real and model butterflies were measured in a wind tunnel as a function of wind speed and body orientation (yaw angle). Results are reported in terms of a dimensionless heat transfer coefficient (Nusselt number, Nu) and a dimensionless wind speed (Reynolds number, Re), for a wind speed range typical of that experienced by basking Colias in the field. The resultant Nusselt-Reynolds (Nu-Re) plots thus indicate the rates of heat transfer by forced convection as a function of wind speed for particular model geometries.For Reynolds numbers throughout the measured range, Nusselt numbers for C. eurytheme butterflies are consistently lower than those for long cylinders, and are independent of yaw angle. There is significant variation among individual butterflies in heat transfer coefficients throughout the Re range. Model butterflies without artificial fur have Nu-Re relations similar to those for cylinders. Heat transfer in these models depends upon yaw angle, with higher heat transfer at intermediate yaw angles (30–60°); these yaw effects increase with increasing Reynolds number. Models with artificial fur, like real Colias, have Nusselt numbers which are consistently lower than those for models without fur at given Reynolds numbers throughout the Re range. Unlike real Colias, however, the models with fur do show yaw angle effects similar to those for models without fur.The independence of heat loss from yaw angle for real Colias is consistent with field observations indicating no behavioral orientation to wind direction. The presence of fur on the models reduces heat loss but does not affect yaw dependence. The large individual variation in heat transfer coefficients among butterflies is probably due to differences in fur characteristics rather than to differences in wing morphology.Finally, a physical model of a butterfly was constructed which accurately simulates the body temperatures of basking Colias in the field for a variety of radiation and wind velocity conditions. The success of the butterfly simulator in mimicking Colias thermal characteristics confirms our preliminary understanding of the physical bases for and heat transfer mechanisms underlying thermoregulatory adaptations in these butterflies.     

Mobile phone exposure and spatial memory

Radiofrequency (RF) emission during mobile phone use has been suggested to impair cognitive functions, that is, working memory. This study investigated the effects of a 2 1/2 h RF exposure (884 MHz) on spatial memory and learning, using a double-blind repeated measures design. The exposure was designed to mimic that experienced during a real-life mobile phone conversation. The design maximized the exposure to the left hemisphere. The average exposure was peak spatial specific absorption rate (psSAR10g) of 1.4 W/kg. The primary outcome measure was a "virtual" spatial navigation task modeled after the commonly used and validated Morris Water Maze. The distance traveled on each trial and the amount of improvement across trials (i.e., learning) were used as dependent variables. The participants were daily mobile phone users, with and without symptoms attributed to regular mobile phone use. Results revealed a main effect of RF exposure and a significant RF exposure by group effect on distance traveled during the trials. The symptomatic group improved their performance during RF exposure while there was no such effect in the non-symptomatic group. Until this new finding is further investigated, we can only speculate about the cause.     

A theoretical study of the reactive dimerization of HCN.

The reaction of two molecules of HCN to produce isomeric forms of (HCN)₂ has been studied theoretically through the use of CNDO/2 calculations together with a method of energy partitioning. The present work predicts that the most stable product of such a reaction is iminoacetonitrile, and that, of the mechanisms considered in the present work, the energetically most favourable, under isolated conditions, involves the dissociation of HCN to free radicals, followed by the reaction of the CN radical with an undissociated HCN molecule and the subsequent addition of hydrogen followed by rearrangement to the imine. However, the energetics are sufficiently similar that an ionic mechanism involving CN^? might be predicted for a condensed, base-catalyzed system.