A new simplified bioheat equation for the effect of blood flow on local average tissue temperature

A new simplified three-dimensional bioheat equation is derived to describe the effect of blood flow on blood-tissue heat transfer. In two recent theoretical and experimental studies [1, 2] the authors have demonstrated that the so-called isotropic blood perfusion term in the existing bioheat equation is negligible because of the microvascular organization, and that the primary mechanism for blood-tissue energy exchange is incomplete countercurrent exchange in the thermally significant microvessels. The new theory to describe this basic mechanism shows that the vascularization of tissue causes it to behave as an anisotropic heat transfer medium. A remarkably simple expression is derived for the tensor conductivity of the tissue as a function of the local vascular geometry and flow velocity in the thermally significant countercurrent vessels. It is also shown that directed as opposed to isotropic blood perfusion between the countercurrent vessels can have a significant influence on heat transfer in regions where the countercurrent vessels are under 70-micron diameter. The new bioheat equation also describes this mechanism.     

The matching of thermal fields surrounding countercurrent microvessels and the closure approximation in the Weinbaum-Jiji equation

A second order perturbation theory is developed to show the difference between the average artery-vein temperature Tm and the local average tissue temperature theta. This theory demonstrates that the closure approximation in the Weinbaum-Jiji bioheat equation does not require that theta = Tm and that although the difference between these two temperatures is second order the magnitude of the countercurrent convection terms in the Weinbaum-Jiji equation can be of order unity. The theory also shows that to second order this new bioheat equation is the same as the simplified set of one-dimensional model equations used in Baish et al.     

A theoretical model for peripheral tissue heat transfer using the bioheat equation of Weinbaum and Jiji

In this paper the new bioheat equation derived in Weinbaum and Jiji is applied to the three layer conceptual model of microvascular surface tissue organization proposed in. A simplified one-dimensional quantitative model of peripheral tissue energy exchange is then developed for application in limb and whole body heat transfer studies. A representative vasculature is constructed for each layer and the enhancement in the local tensor conductivity of the tissue as a function of vascular geometry and blood flow is examined. Numerical solutions for the boundary value problem coupling the three layers are presented and these results used to study the thermal behavior of peripheral tissue for a wide variety of physiological conditions from supine resting state to maximum exercise.     

On the relation between residue flexibility and local solvent accessibility in proteins

We investigate the relationship between the flexibility, expressed with B‐factor, and the relative solvent accessibility (RSA) in the context of local, with respect to the sequence, neighborhood and related concepts such as residue depth. We observe that the flexibility of a given residue is strongly influenced by the solvent accessibility of the adjacent neighbors. The mean normalized B‐factor of the exposed residues with two buried neighbors is smaller than that of the buried residues with two exposed neighbors. Inclusion of RSA of the neighboring residues (local RSA) significantly increases correlation with the B‐factor. Correlation between the local RSA and B‐factor is shown to be stronger than the correlation that considers local distance‐ or volume‐based residue depth. We also found that the correlation coefficients between B‐factor and RSA for the 20 amino acids, called flexibility‐exposure correlation index, are strongly correlated with the stability scale that characterizes the average contributions of each amino acid to the folding stability. Our results reveal that the predicted RSA could be used to distinguish between the disordered and ordered residues and that the inclusion of local predicted RSA values helps providing a better contrast between these two types of residues. Prediction models developed based on local actual RSA and local predicted RSA show similar or better results in the context of B‐factor and disorder predictions when compared with several existing approaches. We validate our models using three case studies, which show that this work provides useful clues for deciphering the structure–flexibility–function relation. Proteins 2009. © 2009 Wiley‐Liss, Inc.     

Fertile sporophore production of Typhula phacorrhiza in the field is related to temperatures near freezing

Two field tests and one lab test were conducted to examine the environmental factors affecting sporophore production in Typhula phacorrhiza and to compare these results with those documented for T. ishikariensis and T. incarnata. In the 2001 lab test where lighting, soil moisture, and soil-sand media were tested in 50 mL screw-cap tubes incubated at 4 degrees C, the limiting factor for Typhula sporophore production was found to be moisture. In the fall 2001 field test, 100 sclerotia of six isolates from three Typhula spp. were placed into pots filled with a sand and soil mixture. The pots were monitored weekly, and maximum sporophore production for all six isolates and for watered and unwatered pots was observed at 11 weeks, which was soon after mean daily temperatures fell below 0 degrees C. In the second field test in fall 2003, five isolates of the three species were tested with similar procedures, but peak sporophore production was observed after 6 weeks, and again only after mean daily temperatures fell below 0 degrees C. In the field, sporophore production of T. phacorrhiza seems to require the same environmental cues as those of T. ishikariensis or T. incarnata, namely high moisture and temperatures near freezing.     

Biometric relation between body size and otolith size of seven commercial fish species of the south‐western Atlantic

Given the importance and applicability of these biometric relations, the present work aimed to verify the existence of correlations between the length of saggitae otoliths and the body size of seven south‐western Atlantic marine fish species and to generate equations to estimate the body size of these species through otolith measurements. Fifty otoliths of Centropomus parallelus, Centropomus undecimalis, Lutjanus analis, Lutjanus jocu, Lutjanus synagris, Chaetodipterus faber and Mugil curema were collected for analysis. Significant relations between otolith length and total length and otolith width and total length were found for all the species. The highest coefficient of determination was observed for Centropomus undecimalis and Lutjanus synagris, for both relations, and the lowest was observed for Mugil curema. The results show that estimates of body size of the species through biometric analyses of otoliths are reliable. Based on this, the equations generated to obtain the total length of the fish using biometric otolith data can be used in dietary studies of top predators and in paleontological recostructions of modern fish.     

On the evolution of brain size in relation to migratory behaviour in birds

Migratory birds appear to have relatively smaller brain size compared to sedentary species. It has been hypothesized that initial differences in brain size underlying behavioural flexibility drove the evolution of migratory behaviour; birds with relatively large brains evolved sedentary habits and those with relatively small brains evolved migratory behaviour (migratory precursor hypothesis). Alternative hypotheses suggest that changes in brain size might follow different behavioural strategies and that sedentary species might have evolved larger brains because of differences in selection pressures on brain size in migratory and nonmigratory species. Here we present the first evidence arguing against the migratory precursor hypothesis. We compared relative brain volume of three subspecies of the white-crowned sparrow: sedentary Zonotrichia leucophrys nuttalli and migratory Z. l. gambelii and Z. l. oriantha. Within the five subspecies of the white-crowned sparrow, only Z. l. nuttalli is strictly sedentary. The sedentary behaviour of Z. l. nuttalli is probably a derived trait, because Z. l. nuttalli appears to be the most recent subspecies and because all species ancestral to Zonotrichia as well as all older subspecies of Z. leucophrys are migratory. Compared to migratory Z. l. gambelii and Z. l. oriantha, we found that sedentary Z. l. nuttalli had a significantly larger relative brain volume, suggesting that the larger brain of Z. l. nuttalli evolved after a switch to sedentary behaviour. Thus, in this group, brain size does not appear to be a precursor to the evolution of migratory or sedentary behaviour but rather an evolutionary consequence of a change in migratory strategy.     

Variation in the size and sensitivity of a genital sensory field in relation to the estrous cycle in rats

In rats showing normal estrous cycles, the size and sensitivity of the pudendal nerve's sensory field was determined by recording spike potentials from the pudendal nerve. The overall sensory field area was larger and more sensitive in estrous than in diestrous females. This indicates that the field's characteristics can change within 2 days (the interval between diestrus and estrus), perhaps as a result of the increased estrogen secretion that occurs around the time of mating. One effect of this increased estrogen secretion may be to sensitize and to enlarge the sensory field of the pudendal nerve. In a second experiment, we found that the genital area of the female which the male's penis contacts during an intromittive mount corresponds closely to an area of high sensitivity within the sensory field of the pudendal nerve. We suggest that the male rat's copulatory contact with this region of the female's perineum may facilitate the intensity of her lordosis and/or her orienting for intromission.     

Importance of alignment between local DC magnetic field and an oscillating magnetic field in responses of brain tissue in vitro and in vivo

The frequency dependence of the electric and magnetic (EM)-field-induced release of calcium ions from an in vitro brain tissue preparation has been shown to be a function of the density of the local DC magnetic field (Bdc). In this study, we demonstrate that the relative orientation of the Bdc and the magnetic component (Bac) of a 315-Hz EM signal (15 Vrms/m and 61 nTrms) are crucial for the induced release to be observed. The induced release occurs only when the Bdc and the Bac are perpendicular, and not when they are parallel. This finding is consistent with a magnetic resonance-like transduction mechanism for the conversion of EM energy into a physicochemical change, and contrasts with the requirement for parallel Bdc and Bac components in the diatom-mobility experiments of Smith et al. A review of the exposure conditions in the rat behavioral experiments conducted by Thomas et al. identifies unhydrated calcium and zinc ions as alternatives to lithium ions as candidates for interaction under parallel magnetic-field orientations but fails to reject perpendicular orientations as an alternative basis for the phenomenon. Investigators that attempt to confirm the rat behavioral experiments should be aware of the conflicting exposure conditions that can be assumed to be operative, and they should design their experiments to test all conditions accordingly.     

The relation between the size of plant and the spread of systemic diseases; the aphis-borne potato virus diseases

It is an implication of systemic infection by the aphis-borne viruses that potato plants with large haulms should be specially vulnerable to infection, and this implication is supported by evidence in the field.
Haulms are reduced in size by short days, low temperatures, under-nutrition and varietal differences. Certain observations are adduced to show that these factors reduce vulnerability. It is suggested that the transference of the potato from the short days, infertile soils and primitive cultivation on the Andes to the long summer days and productive farming of Europe and North America enhanced its vulnerability to aphis-borne virus diseases: the further effects of changes of temperature and manurial practices in the last century need elucidation.