An appratus for counter-current distribution in a centrifugal acceleration field

An apparatus is described that reduces the time required for counter-current distribution in aqueous polymer two-phase systems by a factor of more than five. Phase settling, which has been the time consuming step, is here facilitated by centrifugation. The crucial point in the construction, that allows automatization, is that the transfer step in the counter-current distribution cycle is performed during centrifugation.     

Counter current transfer of PGF2 alpha in the mesometrial vessels as a mechanism for prevention of luteal regression in early pregnancy

A new concept has been presented on the mechanism protecting the corpus luteum during oestrous cycle, early pregnancy and pseudopregnancy induced by oestrogens. The concept is based on the recently discovered mechanism of back transfer of prostaglandin F2 alpha from the broad ligament vasculature into the uterus and on the participation of oestrogen in this process. The morphological facilitates for counter-current transfer of PGF2 alpha in the area of mesometrial vasculature and ability the uterus to bind PGF2 alpha were presented. It has been concluded that the process of PGF2 alpha back-transfer from mesometrial vasculature into the uterus may reduce in uterine venous blood the amplitude of PGF2 alpha pulses and by this way may reduce the penetration of prostaglandin into subovarian area and from there to the corpus luteum.     

Evidence of a counter-current heat exchanger in the ray, Mobula tarapacana (Chondrichthyes: Elasmobranchii: Batoidea: Myliobatiformes)

A vascular network, or rete, has been found in the pectoral fin of the mobulid ray, Mobula tarapacana. This rete appears to be a counter-current heat exchanger which, in conjunction with a high level of red muscle, indicates that this ray is warm-bodied. Preliminary results on other closely related rays indicate that retia may be more common amongst the rays than previously thought.     

Distribution of mass transfer rate and wall shear stress behind simple rectangular stenosis in pulsating flow

The distributions of mass transfer rate and wall shear stress in sinusoidal laminar pulsating flow through a two-dimensional asymmetric stenosed channel have been studied experimentally and numerically. The distributions are measured by the electrochemical method. The measurement is conducted at a Reynolds number of about 150, a Schmidt number of about 1000, a nondimensional pulsating frequency of 3.40, and a nondimensional flow amplitude of 0.3. It is suggested that the deterioration of an arterial wall distal to stenosis may be greatly enhanced by fluid dynamic effects.     

Respiratory system model for quasistatic pulmonary pressure-volume (P-V) curve: generalized P-V curve analyses

A normalized P-V curve is proposed for quantitative comparisons of quasistatic P-V curves from different sources, including data from different investigators, airway pressure-volume curves versus transpulmonary pressure-volume curves, normal versus injured respiratory system, and animal tests versus clinical data. Similarities and differences among five different data groups we analyzed are shown to be quantified through the nondimensional pressure range of an individual data set, combined with the magnitudes of two nondimensional parameters of the inflation limb, derived from a respiratory system model previously reported.     

General characteristics of the sigmoidal model equation representing quasi-static pulmonary P-V curves.

A pulmonary pressure-volume (P-V) curve represented by a sigmoidal model equation with four parameters, V(P) = a + b[1 + exp[-(P - c)/d]](-1), has been demonstrated to fit inflation and deflation data obtained under a variety of conditions extremely well. In the present report, a differential equation on V(P) is identified, thus relating the fourth parameter, d, to the difference between the upper and the lower asymptotes of the volume, b, through a proportionality constant, alpha, with its order of magnitude of 10(-4) to 10(-5) (in ml(-1). cmH(2)O(-1)). When the model equation is normalized using a nondimensional volume, (-1 < < 1), and a nondimensional pressure, (=(p/c) - 1), the resulting - curve depends on a single nondimensional parameter, Lambda = alphabc. A nondimensional work of expansion/compression, (1-2), is also obtained along the quasi-static sigmoidal P-V curve between an initial volume (at 1) and a final volume (at 2). Six sets of P-V data available in the literature are used to show the changes that occur in these two parameters (Lambda defining the shape of the sigmoidal curve and (1-2) accounting for the range of clinical data) with different conditions of the total respiratory system. The clinical usefulness of these parameters requires further study.     

A Three-Dimensional Finite Element Analysis of Heat Transfer in the Forearm

The finite element method was used to analyze heat transfer within a section of the forearm while exposed to different ambient conditions and with different metabolic states. The three-dimensional model accounts for the different material properties of bone, muscle and blood and incorporates a single artery-vein pair for counter-current heat exchange. The geometry of the model was developed from anatomical cross-sectional images of the forearm. The model was used to determine the effects or rest vs. exercise, free vs. forced surface convection and 0 degrees C vs. -20 degrees C external temperatures. The results of the model were compared to experimental data and the model exhibits qualitatively correct behaviour. This model can be used to study hyperthermia, burns and cryogenic freezing of tissue.     

Heat capacities of transfer of some amino acids and peptides from water to aqueous urea solution

Integral enthalpies of solution at low concentrations of several amino acids and peptides in 2 and 6M urea solutions have been determined at 25 and 35°C. These data have been used to derive the enthalpies of transfer (at 25 and 35°C) and heat capacities of transfer (at 30°C) of these amino acids and peptides from water to aqueous urea solutions. Furthermore, the enthalpies of transfer and heat capacities of transfer per CH₂ group and per peptide group ? CONH? have also been estimated. These results show that while the enthalpies and heat capacities of transfer per CH₂ group are positive and negative, respectively, the reverse is true for ? CONH? group. The implications of these results in the mechanism of the denaturation of proteins by urea are discussed.     

Suitability of frequency modulated thermal wave imaging for skin cancer detection—A theoretical prediction

A theoretical study on the quantification of surface thermal response of cancerous human skin using the frequency modulated thermal wave imaging (FMTWI) technique has been presented in this article. For the first time, the use of the FMTWI technique for the detection and the differentiation of skin cancer has been demonstrated in this article. A three dimensional multilayered skin has been considered with the counter-current blood vessels in individual skin layers along with different stages of cancerous lesions based on geometrical, thermal and physical parameters available in the literature. Transient surface thermal responses of melanoma during FMTWI of skin cancer have been obtained by integrating the heat transfer model for biological tissue along with the flow model for blood vessels. It has been observed from the numerical results that, flow of blood in the subsurface region leads to a substantial alteration on the surface thermal response of the human skin. The alteration due to blood flow further causes a reduction in the performance of the thermal imaging technique during the thermal evaluation of earliest melanoma stages (small volume) compared to relatively large volume. Based on theoretical study, it has been predicted that the method is suitable for detection and differentiation of melanoma with comparatively large volume than the earliest development stages (small volume). The study has also performed phase based image analysis of the raw thermograms to resolve the different stages of melanoma volume. The phase images have been found to be clearly individuate the different development stages of melanoma compared to raw thermograms.     

Thermoregulatory physiology of the carpenter bee,Xylocopa varipuncta

Summary The carpenter beesXylocopa varipuncta maintain thoracic temperatures of 33.0°C to 46.5°C during continuous free flight from 12°C to 40°C. Since the thoracic temperature excess is not constant (decreasing from 24°C at low air temperatures to 6°C at high) the bees are thermoregulating. We document physiological transfer of relatively large amounts of heat to the abdomen and to the head during pre-flight warm-up and during artificial thoracic heating. Most of the temperature increase of the head is due to passive conduction, while that of the abdomen is due to active physiological heat transfer despite a series of convolutions of the aorta in the petiole that anatomically conform to a counter-current heat exchanger. Although the thermoregulatory mechanisms during flight are far from clarified, our data suggest that thermoregulation involves a strong reliance on active convective cooling through increased flight speed.     

The use of counter-current distribution to examine the effect of damaging agents on DNA

Mammalian DNA's were separated using a counter-current distribution system for demonstrating alteration in secondary structure after heat denaturation and drug treatment. By using this method a complete separation of native and denatured DNA was achieved. Although the separation of DNA depends on the temperature used for denaturation, the counter-current distribution pattern did not follow exactly the hyperchromic shift. The results suggest that counter-current distribution offers a complementary approach for the study of DNA secondary structure as this method reveals alterations occurring over a wider temperature range than the increase in ultraviolet absorption. The changes in distribution pattern demonstrate cross-linkage occurring with nitrogen mustard and single-strand breaks following methylene dimethanesulphonate (MDMS) treatment in vitro.     

Fractionation of cellulase and beta-glucosidase in a Trichoderma reesei culture liquid by use of two-phase partitioning

An aqueous two-phase system based on the two polymers poly(ethylene glycol) and dextran has been used for the fractionation of cellulase enzymes present in culture liquid obtained by fermentation with Trichoderma reesei. The activities of beta-glucosidase and glucanases were separated to high degree by using the two-phase systems for a counter-current distribution process in nine transfer steps. While the glucanases had high affinity to the poly(ethylene glycol) rich top phase the beta-glucosidase was enriched in the dextran-containing bottom phase. Multiple counter-current distribution performed indicates the heterogeneity of beta-glucosidase activities assuming at least four isoenzyme forms. One step concentration of beta-glucosidase by using system with 46:1 phase volume ratio resulted in 16 times higher enzyme activity.     

A Three-Dimensional Finite Element Analysis of Heat Transfer in the Forearm

Abstract

The finite element method was used to analyze heat transfer within a section of the forearm while exposed to different ambient conditions and with different metabolic states. The three-dimensional model accounts for the different material properties of bone, muscle and blood and incorporates a single artery-vein pair for counter-current heat exchange. The geometry of the model was developed from anatomical cross-sectional images of the forearm. The model was used to determine the effects or rest vs. exercise, free vs. forced surface convection and 0°C vs. — 20 °C external temperatures. The results of the model were compared to experimental data and the model exhibits qualitatively correct behaviour. This model can be used to study hyperthermia, burns and cryogenic freezing of tissue.     

An Innovative Micro-Modelling of Simultaneous Heat and Moisture Transfer during Bread Baking Using the Lattice Boltzmann Method

A considerable fraction of the energy consumed in bread manufacturing is used for the baking process. A thorough understanding of internal moisture transfer mechanisms are important to optimise both the quality of the product and the economics of the process. From a transport phenomena point of view, bread baking has been considered as a simultaneous heat and mass transfer problem in a porous medium. Nevertheless, most efforts previously made have avoided modelling the phenomenon occurring in the microscale, although the mechanism occurs primarily in the microscale. In this work heat and moisture transfer models were developed to accomplish the mechanisms included, both in the microscale and the macroscale by means of Boltzmann’s equation. Modelling and predictions of moisture transfer, heat transfer, modelling of effective moisture diffusivity, thermal conductivity and diffusivity have been investigated in this work. The microstructure in the dough samples was obtained using micro-computer tomography images from the samples prior to baking. The models were quantified and validated with measurements from the literature in order to assess the predictive models. The simulated crust development has shown a crust thickness of 0.8 cm, which is slightly higher than similar experimental results in which a dehydrated thickness of 0.5–0.6 cm was reported. The crust over-estimation in this work fits to the overheating occurring in the model. Additionally, investigations were made on the influence of different porosities (11–16%) of the bread; the boundary layer temperature at a porosity of 11% was reached after 25 min and after 17.5 min at a porosity of 16%. Therewith, the results showed that, with increasing porosity, the heat transfer rate towards the centre was higher, which matches the knowledge of experienced bakers.     

Molecular dynamics simulation of helium–argon gas mixture under various wall conditions

As computational capabilities increase, molecular dynamics (MD) simulations become important tools of simulating reality. These simulations are especially useful for compressible gas mixture problems. In this study, binary diffusion of helium and argon was examined using a hard-sphere MD simulation method. For the sake of computational speed, low spacing ratios were chosen. Binary mass diffusion of gases in two equally sized halves of a box was simulated for identical initial kinetic energies and number densities. It has been noted that a purely mass diffusion mechanism of different gases is not physically possible. The resultant gas mixtures of several diffusion simulations were used as initial conditions for combined heat transfer – Couette flow, and heating and cooling experiments. The results showed the interesting behaviour of the mixture, which was subjected to various wall conditions. Energy of heavier molecules is found to be more sensitive to the wall velocities and less sensitive to the wall temperatures than lighter molecules. Diffusion, heat transfer, viscosity and heat capacity coefficients are deduced as well.     

Experimental investigation of interactions between the temperature field and biofouling in a synthetic treated sewage stream

Biofouling causes significant losses in efficiency in heat exchangers recovering waste heat from treated sewage. The influence of the temperature field on biofouling was investigated using a flat plate heat exchanger which simulated the channels in a plate and frame unit. The test surface was a 316 stainless steel plate, and a solution of Bacillus sp. and Aeromonas sp. was used as a model process liquid. The test cell was operated under co-current, counter-current, and constant wall temperature configurations, which gave different temperature distributions. Biofouling was monitored via changes in heat transfer and biofilm thickness. The effect of uniform temperature on biofouling formation was similar to the effect of uniform temperature on planktonic growth of the organisms. Further results showed that the temperature field, and particularly the wall temperature, influenced the rate of biofouling strongly. The importance of wall temperature suggests that fouling could be mitigated by using different configurations in summer and winter.