Experimental study on convective heat transfer coefficient of the human body

1. 1. The convective heat transfer coefficient of the human body is essential to predict convective heat loss from the body.

2. 2. The object of this paper is to calculate the convective heat transfer coefficient of the human body using heat flow meters and to estimate the thermally equivalent sphere and cylinder to the human body.

3. 3. The experimental formulae of the convective heat transfer coefficient for the whole body were obtained by regression analysis for natural, forced and mixed convection.

4. 4. Diameters of the thermally equivalent sphere and cylinder of the human body were calculated as 12.9 and 12.2 cm, respectively.

Paradox: increased blood perfusion to the face <Emphasis Type="BoldItalic">enhances</Emphasis> protection against frostbite while it <Emphasis Type="BoldItalic">lowers</Emphasis> wind chill equivalent temperatures

A model of facial heat exchange in cold and windy environments is presented. The tissue is depicted as a hollow cylinder and the model includes heat conduction and heat transport by blood circulation from the warmer core. A steady-state solution facilitating the estimation of wind chill equivalent temperature (WCET) as a function of the effective wind velocity, air temperature and blood perfusion rate was obtained. The results quantify and demonstrate the elevation of skin temperatures caused by increased flow of warmer blood from the inner core to the face. Elevated facial temperatures, while enhancing protection against frostbite and other cold-related injuries, also increase heat loss to the colder environment. Paradoxically, such elevated facial temperatures cause WCETs, as estimated by the prevailing definition, to attain lower rather than higher values, indicating, in fact, increased risk of frostbite. The results of this study should be useful in understanding and quantifying the effects of blood perfusion in protection against cold-related injuries. They should also be considered in the re-evaluation and re-formulation of the concept of wind chill, which has been a useful cold weather indicator for decades.     

Factors affecting the resistance to heat transfer provided by clothing

1. 1. This paper discusses the factors that affect the insulation and evaporative resistance provided by clothing.

2. 2. These include: fabric thickness and density, the amount of body surface area covered by garments, the evenness of the distribution of fabrics over the body surface, the increase in surface area for heat loss due to clothing, the looseness or tightness of fit, a person's body position (seated vs standing), body motion and wind.

Cold shock and heat shock: a comparison of the protection generated by brief pretreatment at less severe temperatures

Abstract Brief exposure to low (0^oC) or high (40^oC) temperature elicits a protective response that prevents injury when the flesh fly, Sarcophaga crassipalpis Macquart, is subjected to more severe cold (-10^oC) or heat (45^oC). Both the low and high temperature responses were found in all developmental stages of the fly, but were most pronounced in the pupal and pharate adult stages. The protective responses generated by brief exposure to 0 or 40^oC appear similar in that both result in a rapid acquisition of cold or heat tolerance and a loss of protection after the flies are returned to 25^oC. The protection generated by chilling is obvious within 10 min of exposure to 0^oC while a 30 min exposure to 40^oC is required to induce the high temperature protection. High temperature protects against cold shock injury within a narrow range (around 36^oC) but we have no evidence that low temperature can protect against heat injury. We previously demonstrated that the rapid increase in cold tolerance correlates with concomitant increases in glycerol concentration, but in this study we found no significant elevation in glycerol in heat-shocked flies. Thus the physiological and biochemical bases for the rapid responses to cold and heat appear to be different.     

Relations between heat transfer in perfused biological tissue and the local symmetry components of the vascular system

The relation between perfusion and heat transfer in tissue can be formulated in terms of local symmetry components of the vascular system. It is shown that the order of symmetry (dipole, quadrupole etc. symmetry) gives the order of magnitude of perfusion heat transfer. A unidirectional flow component results in a D'Arcy like bulk flow. A non unidirectional flow component contributes to heat transfer at least by a second order term. It acts like an additional effective heat diffusivity. Comparison with experiments confirm the theoretical results.Supported by Deutsche Forschungsgemeinshcaft.     

On the excited-state energy transfer between tryptophan residues in proteins: the case of penicillin acylase

The problem, whether excited-state energy transfer occurs between Trp residues in a multi-tryptophan proteins and if it does, what kind of changes it induces in different parameters of protein fluorescence, is currently under active investigation. In our previous paper [Biophys. Chem. 72 (1998) 265], the energy transfer was found and studied in detail for Na,K-ATPase. It was shown that this transfer influences all parameters of fluorescence emission, which is detected at site-selective conditions (red-edge of excitation, blue and red edges of emission). Present experiments were performed on unusually tryptophan-rich protein, bacterial penicillin acylase (28 Trp per dimer of 82 kDa) and were aimed to extend these observations. They demonstrate substantial heterogeneity in the environments of tryptophan residues within the protein structure. This suggests, that in the present case, if the energy transfer exists, it should be directed from short-wavelength-emitting to long-wavelength-emitting tryptophan residues and thus could be easily observed by a number of time-resolved and steady-state fluorescence techniques. Unexpectedly, no signature of inter-tryptophan energy transfer was found.     

Syngas fermentation to biofuel: Evaluation of carbon monoxide mass transfer coefficient (kLa) in different reactor configurations

Lignocellulosic biomass such as agri‐residues, agri‐processing by‐products, and energy crops do not compete with food and feed, and is considered to be the ideal renewable feedstocks for biofuel production. Gasification of biomass produces synthesis gas (syngas), a mixture primarily consisting of CO and H₂. The produced syngas can be converted to ethanol by anaerobic microbial catalysts especially acetogenic bacteria such as various clostridia species.One of the major drawbacks associated with syngas fermentation is the mass transfer limitation of these sparingly soluble gases in the aqueous phase. One way of addressing this issue is the improvement in reactor design to achieve a higher volumetric mass transfer coefficient (k_La). In this study, different reactor configurations such as a column diffuser, a 20‐μm bulb diffuser, gas sparger, gas sparger with mechanical mixing, air‐lift reactor combined with a 20‐μm bulb diffuser, air‐lift reactor combined with a single gas entry point, and a submerged composite hollow fiber membrane (CHFM) module were employed to examine the k_La values. The k_La values reported in this study ranged from 0.4 to 91.08 h^?1. The highest k_La of 91.08 h^?1 was obtained in the air‐lift reactor combined with a 20‐μm bulb diffuser, whereas the reactor with the CHFM showed the lowest k_La of 0.4 h^?1. By considering both the k_La value and the statistical significance of each configuration, the air‐lift reactor combined with a 20‐μm bulb diffuser was found to be the ideal reactor configuration for carbon monoxide mass transfer in an aqueous phase. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2011     

Predicting radionuclide transfer to wild animals: an application of a proposed environmental impact assessment framework to the Chernobyl exclusion zone

A number of assessment frameworks have been proposed to provide a mechanism to demonstrate protection of the environment from ionising radiation. Whilst some of these are being used for assessment purposes they have largely not been validated against field measurements. In this paper we compare the predictions of transfer parameters recommended by one of these frameworks (FASSET) with observed whole-body 90Sr and radiocaesium activity concentrations in a range of mammal and invertebrate species sampled within the Chernobyl exclusion zone. Predicted activity concentrations were generally within the observed ranges and mean predictions for reference organisms were similar to, or circa one order of magnitude higher than, the observed means. However, some predictions were more than one order of magnitude lower than observed values. No data were available to test predictions for the other radionuclides released by the Chernobyl accident. In a separate paper the outputs of this assessment will be used to estimate doses to reference organisms and compare these to observed radiation induced effects reported within the Chernobyl zone.     

Effect of organic solvents on oxygen mass transfer in multiphase systems: Application to bioreactors in environmental protection

The absorption of oxygen in aqueous–organic solvent emulsions was studied in a laboratory-scale bubble reactor at a constant gas flow rate. The organic and the gas phases were dispersed in the continuous aqueous phase. Volumetric mass transfer coefficients (k_La) of oxygen between air and water were measured experimentally using a dynamic method. It was assumed that the gas phase contacts preferentially the water phase. It was found that addition of silicone oils hinders oxygen mass transfer compared to air–water systems whereas the addition of decane, hexadecane and perfluorocarbon PFC40 has no significant influence. By and large, the results show that, for experimental conditions (organic liquid hold-up ≤10% and solubility ratio ≤10), the k_La values of oxygen determined in binary air–water systems can be used for multiphase (gas–liquid–liquid) reactor design with applications in environmental protection (water and air treatment processes).     

Effects of environmental conditions on the fixation and transfer of nitrogen from alfalfa to associated timothy

Nitrogen fixation (NF) by alfalfa and nitrogen transfer (NT) from alfalfa to associated timothy was studied under different environmental conditions in controlled growth chambers, using the¹⁵N dilution technique. Evidence was obtained of NT from alfalfa to the associated timothy. Conditions that favored NF by alfalfa resulted in an increase in its NT. Of 3 different temperature regimes (25/20, 16/14, and 12/9°C day/night), 16–25/14–20°C was the best range for NF by alfalfa and resulted in the greatest NT. High light intensity (550 uE.m⁻².sec⁻¹) and long days (16–20 h) also caused increased NF by alfalfa and benefitting timothy more than in a regime of low light intensity (by shading 50% or 75%) or short days (12/12 or 16/8 h day/night). When the inoculated (Rhizobium meliloti) root systems of plants were kept free from other microorganisms (axenic condition) to minimize possible decomposition of dead tissues, lower NT from alfalfa was observed, especially at later cuts, compared to non-axenic plants. This suggests that both direct excretion and decomposition of dead alfalfa tissues are sources of N benefit from alfalfa to associated timothy. Contribution no 1065 of the Plant Research Centre.     

A general model for the propagation of uncertainty in measurements into heat transfer simulations and its application to cryosurgery

This report presents a technique for estimating the propagation of uncertainty in measurements into mathematical simulations of heat transfer. The motivation for this report is to show the dramatic uncertainty associated with estimating the value of the so-called "lethal temperature," even in a case where a perfect correlation appears to exist between histo-pathologic observations and a corresponding heat transfer simulation. Although the example presented in this report relates to cryosurgery, the technique proposed in this report is rather general and can be applied to any heat transfer problem. The uncertainty analysis presented in this report can be considered as an extension of the well-known concept of the rule of the square root of the sum of the square errors. A comparison of the new technique with the worst case scenario concept is also presented. In conclusion, it is recommended that the proposed technique be routinely applied when presenting simulated results, whether as a part of a theoretical study, or in comparison with experimental data.     

Direct gene transfer to protoplasts: Fate of the transferred genes

Direct gene transfer to protoplasts is one of several methods developed for the production of transgenic plants. This method utilizes the efficient uptake of DNA from the surrounding medium by protoplasts (cell wall-less plant cells). Where a suitable protoplast system exists large numbers of transformant clones can be efficiently produced and often regenerated to normal fertile plants. This review concentrates on the fate of the DNA which is taken up into the protoplasts. Particular emphasis is given to the factors which can influence the integration and form of the transferred DNA, the expression of transferred genes, and the inheritance in further generations of those genes. The information available suggests (1) that DNA is taken up by a large proportion of the cells in a transformation mixture, (2) that this DNA forms complexes sometimes involving carrier DNA, (3) that fewer cells actually take up DNA into the nucleus, and (4) that the complex may be rearranged and/or amplified and then integrated into the genome. If the DNA is arranged in such a way that a gene can be expressed it does so in a normal manner and is stably inherited both mitotically and meiotically.     

A comparison of the responses of tropical and temperate flies (Diptera: Sarcophagidae) to cold and heat stress

Summary Two flesh fly species from the tropical lowlands (Peckia abnormis and Sarcodexia sternodontis) were more susceptible to both cold-shock and heatshock injury than temperate flies (Sarcophaga crassipalpis and S. bullata) and a fly from a tropical high altitude (Blaesoxipha plinthopyga). A brief (2-h) exposure to 0°C elicits a protective response against subsequent cold injury at–10°C in the temperate flies and in B. plinthopyga but no such response was found in the flies from the tropical lowlands. However, both tropical and temperate flies could be protected against heat injury (45°C) by first exposing them to a mild heat shock (2 h at 40°C). The supercooling point is not a good indicator of cold tolerance: supercooling points of pupae were similar in all species, ranging from–18.9 to–23.0°C, and no differences were found between the tropical and temperate species. Among the temperate species, glycerol, the major cryoprotectant, can be elevated by short-term exposure to 0°C, but glycerol could not be detected in the tropical flies. Low-temperature (0°C) exposure also increased hemolymph osmolality of the temperate species, but no such increase was observed in the tropical lowland species. Adaptations to temperature stress thus differ in tropical and temperate flesh flies: while flies from both geographic areas share a mechanism for rapidly increasing heat tolerance, only the temperate flies appear capable of responding rapidly to cold stress. The presence of a heat shock response in species that lack the ability to rapidly respond to cold stress indicates that the biochemical and physiological bases for these two responses are likely to differ.     

Naturally mosaic operons for secondary metabolite biosynthesis: variability and putative horizontal transfer of discrete catalytic domains of the epothilone polyketide synthase locus

A putative instance of horizontal gene transfer (HGT) involving adjacent, discrete -ketoacyl synthase (KS), acyl carrier protein (ACP) and nonribosomal peptide synthase (NRPS) domains of the epothilone Type I polyketide biosynthetic gene cluster from the myxobacterium Sorangium cellulosom was identified using molecular phylogenetics and sequence analyses. The specific KS domain of the module EPO B fails to cluster phylogenetically with other epothilone KS sequences present at this locus, in contrast to what is typically observed in many other Type I polyketide synthase (PKS) biosynthetic loci. Furthermore, the GC content of the epoB KS, epoA ACP and NRPS domains differs significantly from the base composition of other epothilone domain sequences. In addition, the putatively transferred epothilone loci are located near previously identified transposon-like sequences. Lastly, comparison with other KS loci revealed another possible case of horizontal transfer of secondary metabolite genes in the genus Pseudomonas. This study emphasizes the use of several lines of concordant evidence (phylogenetics, base composition, transposon sequences) to infer the evolutionary history of particular gene and enzyme sequences, and the results support the idea that genes coding for adaptive traits, e.g. defensive natural products, may be prone to transposition between divergent prokaryotic taxa and genomes.Communicated by W. Arber     

Acclimation of entomopathogenic nematodes to novel temperatures: trehalose accumulation and the acquisition of thermotolerance

The effect of thermal acclimation on trehalose accumulation and the acquisition of thermotolerance was studied in three species of entomopathogenic nematodes adapted to either cold or warm temperatures. All three Steinernema species accumulated trehalose when acclimated at either 5 or 35 degrees C, but the amount of trehalose accumulation differed by species and temperature. The trehalose content of the cold adapted Steinernema feltiae increased by 350 and 182%, of intermediate Steinernema carpocapsae by 146 and 122% and of warm adapted Steinernema riobrave by 30 and 87% over the initial level (18.25, 27.24 and 23.97 microg trehalose/mg dry weight, respectively) during acclimation at 5 and 35 degrees C, respectively. Warm and cold acclimation enhanced heat (40 degrees C for 8h) and freezing (-20 degrees C for 4h) tolerance of S. carpocapsae and the enhanced tolerance was positively correlated with the increased trehalose levels. Warm and cold acclimation also enhanced heat but not freezing tolerance of S. feltiae and the enhanced heat tolerance was positively correlated with the increased trehalose levels. In contrast, warm and cold acclimation enhanced the freezing but not heat tolerance of S. riobrave, and increased freezing tolerance of only warm acclimated S. riobrave was positively correlated with the increased trehalose levels. The effect of acclimation on maintenance of original virulence by either heat or freeze stressed nematodes against the wax moth Galleria mellonella larvae was temperature dependent and differed among species. During freezing stress, both cold and warm acclimated S. carpocapsae (84%) and during heat stress, only warm acclimated S. carpocapsae (95%) maintained significantly higher original virulence than the non-acclimated (36 and 47%, respectively) nematodes. Both cold and warm acclimated S. feltiae maintained significantly higher original virulence (69%) than the non-acclimated S. feltiae (0%) during heat but not freezing stress. In contrast, both warm and cold acclimated S. riobrave maintained significantly higher virulence (41%) than the non-acclimated (14%) nematodes during freezing, but not during heat stress. Our data indicate that trehalose accumulation is not only a cold associated phenomenon but is a general response of nematodes to thermal stress. However, the extent of enhanced thermal stress tolerance conferred by the accumulated trehalose differs with nematode species.     

Alteration in chloroplast structure and thylakoid membrane composition due to in vivo heat treatment of rice seedlings: correlation with the functional changes

Exposure of 25 °C-grown, seven-day-old rice seedlings to mild heat stress of 40 °C for 24 h in dark did not cause any change in protein or pigment content of the thylakoids, but produced major disorganization of chloroplast ultrastructure. This heat induced disorganization of thylakoid structure/organization caused significant (65 percnt;) loss in PSII activity, slight loss in PSI activity, and brought about a decrease in relative quantum efficiency of PSII. The herbicide ¹⁴C atrazine binding assay revealed a decreased number of binding sites of the herbicide and altered the herbicide dissociation constant, suggesting that the heat induced disorganization of the thylakoids affects the acceptor side of PSII. Cation induced Chla fluorescence analyses at room temperature and low temperature indicated thatin vivo heat exposure of rice seedlings altered the extent of energy transfer in favor of PSI. Immunoblotting analysis of several PSII polypeptides such as D1/D2 reaction dimer and Cyt b₅₅₉ showed no major changes due to mild heat exposure except for the PSII core antenna polypeptide (CP43), which could reflect the reduction in PSII activity observed in light saturation studies. Similarly, haeme staining did not indicate any change in other cytochrome related polypeptides. Our results therefore clearly suggest thatin vivo exposure of rice seedlings to elevated (40 °C) temperature caused thylakoid structural disorganization, and this disorganization of some of the thylakoid complexes resulted in a loss in thylakoid photochemical function.