Differentiation between acetate and higher volatile acids in the modeling of the anaerobic biomethanation process

This paper presents a model for the single-stage completely-mixed anaerobic digestion of complex substrates containing no volatile acids. In the model, volatile acids produced by the acidogenic bacteria are no longer considered together. Acetate is assumed to be representative of the substrate and propionate and butyrate act only as inhibitors for the methanogenic bacteria.Nomenclature ···0 represents factors associated with the influent - ···1 represents factors associated with the acidogenic bacteria - ···2 represents factors associated with the methanogenic bacteria - Q hydraulic flow (1/d) - V reactor liquid volume (1) - T temperature of the mixed liquor (° C) - S microorganisms concentration (mg/1) - L volatile solids concentration (mg VS/1) - Lb biodegradable volatile solids concentration (mg VS/1) - VA2 acetate concentration (mg/1) - VA3 volatile acids with 3 to 5 carbon atoms concentration (mg/1) - methane rate production (1 CH₄/1_digester.d) - Km saturation coefficient (mg/l) - Ki inhibition coefficient (mg/l) - specific growth rate (1/d) - maximum specific growth rate (1/d) - b biological decay coefficient (1/d) - Arrhénius coefficient (–) - yield of acidogenic bacteria per mg of biodegradable matter consumed (mg S₁/mg L_b) | (mg S₂/mg VA2) - yield of methanogenic bacteria per mg of VA2 consumed - yield of methane production per mg of S₂ formed (1 CH₄/mg S₂) - proportion of VA2 produced per mg of S₁ biosynthetised - proportion of VA3 produced per mg of S₁ biosynthetised - Y_sp volume of CH₄ produced per g of volatile solids eliminated     

Control of acid-base status in active and dormant land snails,Otala lactea (Pulmonata,Helicidae)

Summary Control of extracellular acid-base status was examined during activity and dormancy inOtala lactea (Pulmonata, Helicidae). Active snails showed little variation in hemolymph pH and at constant temperature. With increase of temperature, hemolymph increased from about 6 Torr at 5°C to 13 Torr at 24°C and pH decreased by about 0.017 pH units/°C, a pattern consistent with alphastat regulation of pH via ventilatory control of .During dormancy, mean hemolymph increased to about 50 Torr. Venous pH declined by about 0.4 units due to hypercapnia and fluctuated more widely than in active snails due to variability of . Hemolymph pH declined further in prolonged dormancy due to progressive metabolic acidosis; after one year of dormancy the mean hemolymph pH was about 0.8 units lower than that of active snails at similar temperature.Active snails exposed experimentally to high showed a large increase in hemolymph [HCO ₃ ^– ]. However, [HCO ₃ ^– ] declined by up to 50% during dormancy, despite the naturally occurring hypercapnia. Hemolymph osmolality and the concentrations of solutes other than [HCO ₃ ^– ] increased with increasing duration of dormancy. Concentrations of magnesium and calcium increased about 2.5 times more rapidly than those of sodium and chloride, indicating that acidosis is partially offset by the dissolution of carbonates from the shell or tissues.     

Effects of ambient and local cutaneous temperatures on hand blood flow

The hand blood flow ( ) was investigated in response to a wide range of general and local cutaneous thermal stimuli (0–36°C and 4–42°C respectively), the local stimulus consisting of a thermostatically controlled water bath for the right hand (T_w), and the general stimulus, the ambient room temperature (T_a). was measured at the right wrist by strain gauge plethysmography; it was seen to respond more significantly to variations in T_w than to those in T_a at cold to comfortable ambient temperatures (T_a<22°C). A paradoxical vasodilatation was observed at T_w=4°C (Lewis' hunting phenomenon). The graphs of versus T at average to high local cutaneous temperatures (T_w > 33°C) are remarkably similar, except for an upward shift at successively higher values of T_w. The slope (or vasomotor reactivity) is interpreted as being controlled by variations in T_a. The curves exhibited maximum values at T_a = 31°C. Their subsequent decrease could represent a thermoregulatory adaptation to environment-organism heat transfer, the relative vasoconstriction tending to reduce the transfer. Although the qualitative response was the same for both sexes, the absolute value of was generally greater in male than in female subjects.     

The effect of short-term fasting and a single meal on protein synthesis and oxygen consumption in cod,Gadus morhua

Summary Rates of protein synthesis and oxygen consumption ( O₂) in cod were compared in both fasted and refed animals. During a 14-day fast both protein synthesis and respiration rates fell to stable values after 6 days. When a meal of whole sandeel at 6% body weight was fed to fish fasted for 6 days, protein synthesis and ( O₂) increased to a maximum at between 12 and 18 h after feeding. Peak ( O₂) was about twice the pre-feeding values, while whole animal protein synthesis increased four-fold. There were differences between tissues in the timing of maximum protein synthesis; the liver and stomach responded faster than the remainder of the body. Maximum protein synthesis rates in the liver and stomach occurred at 6 h after feeding, at which time their calculated contribution to total ( O₂) was 11%. Similar calculations suggested that the integrated increment in whole animal protein synthesis contributed between 23% and 44% of the post-prandial increase in ( O₂). It was concluded that protein synthesis is an important contributor to increased ( O₂) after feeding in cod.Abbreviations A _s absolute rate of protein synthesis - ASDA apparent specific dynamic action - ATP adenosine triphosphate - k _s fractional rate of protein synthesis - k _s/RNA amount of protein synthesized per unit RNA - ( O₂) oxygen consumption - PCA perchloric acid - RNA ribonucleic acid     

Aerobic metabolism of the lizardVaranus exanthematicus: Effects of activity, temperature, and size

Summary Oxygen consumption was measured at rest and during spontaneous activity at body temperatures of 25 and 35°C in 14 fasting Savanna monitor lizards,Varanus exanthematicus ranging in weight from 172 to 7500 g. The allometric relationship between metabolic rate at 25°C and body weight (W) is given by: (ml O₂ STPD·g^–1·hr^–1)=0.88W ^–0.43 (Fig. 2). Although statistical comparisons are equivocal, this intraspecific size dependence exceeds that reported for interspecific comparisons among reptiles and other vertebrate groups (Fig 3). A reproducible diurnal pattern of activity was observed in undisturbed animals with minimum values of between 2400 and 0800 h (Fig. 1). Spontaneous activity and generally reached peak values between 1200 and 2000 hrs. The average ratio of active aerobic metabolic rate (AMR) to minimum (standard) aerobic metabolic rate (SMR) was 8.2. This voluntary AMR/SMR inVaranus exceeds the AMR/SMR for most reptiles stimulated to exhaustion. The high aerobic capacity is consistent with other evidence for efficient exchange and transport of respiratory gases inV. exanthematicus; e.g., low or absent intracardiac shunt flow resulting in high arterial saturation and low ventilation and perfusion requirements.     

Thermoregulation,gas exchange,and ventilation in Adelie penguins (Pygoscelis adeliae)

Summary Adelie penguins (Pygoscelis adeliae) experience a wide range of ambient temperatures (T _a) in their natural habitat. We examined body temperature (T _b), oxygen consumption ( ), carbon dioxide production ( ), evaporative water loss ( ), and ventilation atT _a from –20 to 30 °C. Body temperature did not change significantly between –20 and 20°C (meanT _b=39.3°C).T _b increased slightly to 40.1 °C atT _a=30°C. Both and were constant and minimal atT _a between –10 and 20°C, with only minor increases at –20 and 30°C. The minimal of adult penguins (mean mass 4.007 kg) was 0.0112 ml/[g·min], equivalent to a metabolic heat production (MHP) of 14.9 Watt. The respiratory exchange ratio was approximately 0.7 at allT _a. Values of were low at lowT _a, but increased to 0.21 g/min at 30°C, equivalent to 0.3% of body mass/h. Dry conductance increased 3.5-fold between –20 and 30°C. Evaporative heat loss (EHL) comprised about 5% of MHP at lowT _a, rising to 47% of MHP atT _a=30°C. The means of ventilation parameters (tidal volume [VT], respiration frequency [f], minute volume [I], and oxygen extraction [ ]) were fairly stable between –20 and 10°C (VT did not change significantly over the entireT _a range). However, there was considerable inter- and intra-individual variation in ventilation patterns. AtT _a=20–30°C,f increased 7-fold over the minimal value of 7.6 breaths/min, and I showed a similar change. fell from 28–35% at lowT _a to 6% atT _a=30°C.Abbreviations C thermal conductance - EHL evaporative heat loss - oxygen extraction - f respiratory frequency - MHP metabolic heat production - evaporative water loss - LCT lower critical temperature - RE respiratory exchange ratio - T _a ambient temperature - T _b body temperature - rate of oxygen consumption - rate of carbon dioxide production - I inspiratory minute volume - VT tidal volume     

Respiratory responses to long-term temperature exposure in the box turtle,Terrapene ornata

Summary In late February, seven box turtles were collected with body temperatures between 7 and 9°C. Ventilation, gas exchange and end-tidal and were recorded at 5, 10, 15 and 25°C, the animals being at each temperature for 2 to 3 weeks. There was a pronounced diurnal rhythm of breathing frequency at all temperatures. At 5°C the mean 24-h frequency was only 3.7 breaths h^–1. At 15°C the frequency was 16 times higher with a 17-fold increase of ventilation. Oxygen uptake only changed from 3.4 to 12.7 ml·kg^–1·h^–1. Consequently, the ratio (ventilation, ml BTPS/O₂ uptake, ml STPD) increased from 12.5 at 5°C to 48 at 15°C, but decreased to 24 at 25°C. The decrease of this ratio during cold exposure contrasts with an increase of the ratio during cooling earlier reported for fresh water turtles,Pseudemys. Cutaneous CO₂ elimination was important at low temperature. This caused a decrease of the pulmonary gas exchange ratio so that end-tidal remained low at 5°C in spite of an end-tidal of only 54 Torr.     

A method for determining the maximal steady state of blood lactate concentration from two levels of submaximal exercise

The aim of this study was to estimate the characteristic exercise intensity _CL which produces the maximal steady state of blood lactate concentration (MLSS) from submaximal intensities of 20 min carried out on the same day and separated by 40 min. Ten fit male adults [maximal oxygen uptake _max 62 (SD 7) ml · min^–1 · kg^–1] exercisOed for two 30-min periods on a cycle ergometer at 67% (test 1.1) and 82% of _max (test 1.2) separated by 40 min. They exercised 4 days later for 30 min at 82% of _max without prior exercise (test 2). Blood lactate was collected for determination of lactic acid concentration every 5 min and heart rate and O₂ uptake were measured every 30 s. There were no significant differences at the 5th, 10th, 15th, 20th, 25th, or 30th min between , lactacidaemia, and heart rate during tests 1.2 and 2. Moreover, we compared the exercise intensities _CL which produced the MLSS obtained during tests 1.1 and 1.2 or during tests 1.1 and 2 calculated from differential values of lactic acid blood concentration ([1a^–]_b) between the 30th and the 5th min or between the 20th and the 5th min. There was no significant difference between the different values of _CL [68 (SD 9), 71 (SD 7), 73 (SD 6),71 (SD 11) % of _max (ANOVA test,P<0.05). Four subjects ran for 60 min at their _CL determined from periods performed on the same day (test 1.1 and 1.2) and the difference between the [la^–]_b at 5 min and at 20 min ( ([la^–]_b)) was computed. The [la^–]_b remained constant during exercise and ranged from 2.2 to 6.7 mmol · l^–1 [mean value equal to 3.9 (SD 1) mmol · l^–1]. These data suggest that the _CL protocol did not overestimate the exercise intensity corresponding to the maximal fractional utilization of _max at MLSS. For half of the subjects the _CL was very close to the higher stage (82% of _max where an accumulation of lactate in the blood with time was observed. It can be hypothesized that _CL was very close to the real MLSS considering the level of accuracy of [la^–]_b measurement. This study showed that exercise at only two intensities, performed at 65% and 80% of _max and separated by 40 min of complete rest, can be used to determine the intensity yielding a steady state of [la^–1]_b near the real MLSS workload value.     

Electrotransformation of intact and osmotically sensitive cells of Corynebacterium glutamicum

Summary Intact and osmotically sensitive cells of Corynebacterium glutamicum can be efficiently transformed by electroporation. This was shown by using the plasmid vector pUL-330 (5.2 kb), containing the kanamycin resistance gene of transposon Tn5. The following electric parameters yielded efficient transformation. For intact cells: one exponentially decaying field pulse with time constants and with initial field intensities of E ₀=35–40 kV cm^-1; prepulse temperature 20°C. Cell regeneration (survival) was 100%–80%. Transformation efficiency can be increased by an additional freeze and thaw cycle of the cells, prior to electroporation. Lysozyme treated cells (osmotically sensitive) were transformed with three successive pulses of E ₀=25–30 kV cm^-1. Cell regeneration under these conditions was found to be 20–30%. The optimum yield of transformants/g plasmid-DNA was 3×10³ for intact cells, 2×10⁴ for intact cells which were frozen and thawed twice and 7×10⁴ for osmotically sensitive cells if the cell suspension was pulsed at a cell density of 1–3×10⁸/ml and at a DNA concentration of 0.2 g/ml up to 2 g/ml. The data obtained for osmotically sensitive cells suggest that the temperature increase accompanying the electric field pulse enhances colony formation and transformation efficiency if the initial prepulse temperature is 20°C, although regeneration of electroporated C. glutamicum cells starts to decrease at temperatures20°C.     

Ventilatory responses to exercise and carbon dioxide in elderly and younger humans

The present investigation examined the relationship between CO₂ sensitivity [at rest (S _R) and during exercise (S _E)] and the ventilatory response to exercise in ten elderly (61–79 years) and ten younger (17–26 years) subjects. The gradient of the relationship between minute ventilation and CO₂ production ( _E/ CO₂) of the elderly subjects was greater than that of the younger subjects [mean (SEM); 32.8 (1.6) vs 27.3 (0.4); P<0.01]. At rest, S _R was lower for the elderly than for the younger group [10.77 (1.72) vs 16.95 (2.13) 1 · min^–1 · kPa^–1; 1.44 (0.23) vs 2.26 (0.28) 1 · min^–1 · mmHg^–1; P<0.05], but S _E was not significantly different between the two groups [17.85 (2.49) vs 19.17 (1.62) l · min^–1 · kPa^–1; 2.38 (0.33) vs 2.56 (0.21) 1 · min^–1 · mmHg^–1]. There were significant correlations between both S _R and S _E, and _E/ CO₂ (P<0.05; P<0.001) for the younger group, bot none for the elderly. The absence of a correlation for the elderly supports the suggestion that _E/ CO₂ is not an appropriate index of the ventilatory response to exercise for elderly humans.     

Ventilation and gas exchange in the diamondback water snake,Natrix rhombifera

Summary Simultaneous measurements of pulmonary and cutaneous oxygen and carbon dioxide exchange, pulmonary ventilation and heart rate were made on the diamondback water snake,Natrix rhombifera at 28°C using body plethysmography. Resting lung volume, maximum lung volume and tracheal volume were also measured.The following mean values were measured in undisturbed snakes breathing room air: total (pulmonary and cutaneous) O₂ uptake 46 mol · (kg min)^–1; total CO₂ output, 49 mol · (kg min)^–1; tidal volume, 12 ml (BTPS) · kg^–1; ventilatory rate, 6.9 min^–1; heart rate, 42 min^–1. From the measurements of tracheal volume, the effective (alveolar) ventilation was estimated as approximately 70% of total ventilation resulting in effective pulmonary and of 130 Torr and 20 Torr respectively. Cutaneous exchange accounted for 8.1% of the total and 12.4% of the total .Resting lung volume of anaesthetized snakes was 75 ml (BTPS) · kg^–1, maximum lung volume was 341 ml (BTPS) · kg^–1 and tracheal volume was 3.9 ml (BTPS) · kg^–1.     

Effect of temperature and humidity on evaporative water loss in Anna's hummingbird (Calypte anna)

Summary Evaporative water loss (EWL), oxygen concumption , and body temperature (T_b) of Anna's Hummingbirds (Calypte anna; ca. 4.5g) were measured at combinations of ambient temperature (T_a) and water vapor density (_va) ranging from 20 to 37 °C and 2 to 27 g·m^-3, respectively. The EWL decreased linearly with increasing _va at all temperatures. The slopes of least squares regression lines relating EWL to _va at different temperatures were not significantly different and averaged-0.50 mg H₂O·m^-3·g^-2·h^-1 (range:-0.39 to-0.61). Increased _va restricted EWL in C. anna more than has been reported for other endotherms in dry air. The percent of metabolic heat production dissipated by evaporation ( ) was lower than that of other birds in dry air, but higher than that for other birds at high humidity when T_a 33 °C. When T_a>33 °C the effect of humidity on was similar to that in other birds. Calypte anna might become slightly hyperthermic at T_a>37 °C, which could augment heat transfer by increasing the T_b-T_a gradient. Body temperature for C. anna in this study was 43 °C (intramuscular) at T_as between 25 and 35 °C, which is above average for birds. It is estimated that field EWL is less than 30% of daily water loss in C. anna under mild temperature conditions (<35 °C).Abbreviations BMR basal metabolic rate - EWL evaporative water loss - percent of metabolic heat production dissipated by evaporation - ambient water vapor density - body surface water vapor density - RMR resting metabolic rate - T_a ambient-temperature - T_b body temperature - T_d dew-point temperature - TNZ thermoneutral zone - T_s body surface temperature - carbon dioxide production - oxygen consumption     

Maximal oxygen uptake, maximal voluntary isometric contraction and physical activity in young Danish adults

In a randomly selected sample of 88 men and 115 women, aged 23–27 years from Denmark, maximal oxygen uptake ( O_2max), maximal voluntary isometric contraction (MVC) in four muscle groups and physical activity were studied. The O_2max was 48.0 ml · min^–1 kg^–1 and 39.6 ml · min^–1 · kg^–1 for the men and the women, respectively. The MVC was 10% lower than in a comparable group of Danes of the same age and height studied 35 years ago. Only in men was sports activity directly related to O_2max (ml · min^–1 · kg^–1; r=0.31, P<0.01). The MVC of the knee extensors was related to O_2max in the men (r=0.31, P<0.01), but there was no relationship between the other measurements of MVC and O_2max. In the women O_2max (ml · min^–1 · kg^–1) was only related to body size, i.e. body mass index, percentage body fat and body mass [(r= –0.47, –0.48 (both P<0.001) and –0.34. (P<0.01), respectively)]. There were differences in O_2max in the men, according to education and occupation. Blue collar workers and subjects attending vocational or trade schools in 1983 had lower O_2max and more of them were physically inactive. In the women differences were also found, but there was no clear pattern among the groups. More of the women participated regularly in sports activity, but more of the men were very active compared to the women.     

Carbon dioxide desorption from fermentation broth by use of oxygen vectors

The ability of oxygen vector to extract produced carbon dioxide has been tested in an anaerobic fermentation. During the continuous culture of Clostridium acetobutylicum at pH 4.6 and at a dilution rate of 0.124 h^–1, a feed composed of an emulsion of 18.5% by volume of Forane F66E was able to extract about 9% of the total CO₂ produced under CO₂ partial pressure equal to 0.42 atm. A theoretical evaluation of the extracted amount, based on the hypothesis of total saturation of the vector by carbon dioxide, has lead to very good agreement.List of Symbols [AA] g/l acetic acid concentration - [BA] g/l butyric acid concentration - D 1/h Q _w /V dilution rate - [ETH] g/l ethanol concentration - H _w Henry constant of CO₂ for water at 37°C (=23.91 mmol/(l atm)) - H _F Henry constant of CO₂ for Forane at 37°C (=83.4 mmol/(l atm)) - H _i g/mol molar mass of componenti - P _i atm partial pressure of gasi - W _w l/h aqueous flow - Q_f 1/h Forane flow - mmol/(lh) dissolved CO₂ flow in aqueous effluent - mmol/(lh) CO₂ gas flow - mmol/(lh) CO₂ gas flow without Forane - mmol/(lh) CO₂ gas flow with Forane - mmol/(lh) total CO₂ production - r _X g/(lh) biomass production rate - r _G mmol/(lh) total gas flow - mmol/(lh) hydrogen production - mmol/(lh) nitrogen flow - r _S mmol/(lh) glucose input - V 1 fermentor volume     

Consequences of skin color and fur properties for solar heat gain and ultraviolet irradiance in two mammals

Summary In animals with fur or feather coats, heat gain from solar radiation is a function of coat optical, structural, and insulative characteristics, as well as skin color and the optical properties of individual hairs or feathers. In this analysis, I explore the roles of these factors in determining solar heat gain in two desert rodents (the Harris antelope squirrel,Ammospermophilus harrisi, and the round-tailed ground squirrel,Spermophilus tereticaudus). Both species are characterized by black dorsal skin, though they contrast markedly in their general coat thickness and structure. Results demonstrate that changes in coat structure and hair optics can produce differences of up to 40% in solar heat gain between animals of similar color. This analysis also confirms that the model of Walsberg et al. (1978) accurately predicts radiative heat loads within about 5% in most cases. Simulations using this model indicate that dark skin coloration increases solar heat gain by 5%. However, dark skin significantly reduces ultraviolet transmission to levels about one-sixth of those of the lighter ventral skin.Symbols and abbreviations: (unless noted, all radiation relations refer to total solar radiation) absorptivity of individual hairs - _C absorptivity of the coat - backward scattering coefficient [reflectivity] of individual hairs - _C reflectivity of coat - _S reflectivity of skin - forward scattering coefficient [transmissivity] of individual hairs - _C transmissivity of coat - _S transmissivity of the skin - transmissivity of the coat and skin - transmissivity of the coat to ultraviolet radiation - _S transmissivity of the skin to ultraviolet radiation - [(1 – )² – ²] - h _C coat thermal conductance [W/m²-°C] - h _E coat surface-to-environment thermal conductance [W/m²-°C] - I probability per unit coat depth that a ray will be intercepted by a hair [m^–1] - K volumetric specific heat of air at 20°C [1200 J/m³-°C] - l _C coat thickness [m] - l _H hair length [m] - d hair diameter [m] - n hair density per unit skin area (m^–2] - Q _ABS heat load on animal's skin from solar radiation [W/m²] - Q _I solar irradiance at coat surface [W/m²] - r _E external resistance to convective and radiative heat transfer [s/m] - r _C coat thermal resistance [s/m]     

Flight of the honey bee VI: energetics of wind tunnel exhaustion flights at defined fuel content,speed adaptation and aerodynamics

To gain information on extended flight energetics, quasi-natural flight conditions imitating steady horizontal flight were set by combining the tetheredflight wind-tunnel method with the exhaustion-flight method. The bees were suspended from a two-component aerodynamic balance at different, near optimum body angle of attack and were allowed to choose their own speed: their body mass and body weight was determined before and after a flight; their speed, lift, wingbeat frequency and total flight time were measured throughout a flight. These values were used to determine thrust, resultant aerodynamic force (magnitude and tilting angle), Reynolds number, total flight distance and total flight impulse. Flights in which lift was body weight were mostly obtained. Bees, flown to complete exhausion, were refed with 5, 10, 15 or 20 l of a 1.28-mol·l^-1 glucose solution (energy content w=18.5, 37.0, 55.5 or 74.0 J) and again flown to complete exhaustion at an ambient temperature of 25±1.5°C by a flight of known duration such that the calculation of absolute and relative metabolic power was possible. Mean body mass after exhaustion was 76.49±3.52 mg. During long term flights of 7.47–31.30 min similar changes in flight velocity, lift, thrust, aerodynamic force, wingbeat frequency and tilting angle took place, independent of the volume of feeding solution. After increasing rapidly within 15 s a more or less steady phase of 60–80% of total flight time, showing only a slight decrease, was followed by a steeper, more irregular decrease, finally reaching 0 within 20–30 s. In steady phases lift was nearly equal to resultant aerodynamic force; tilting angle was 79.8±4.0°, thrust to lift radio did not vary, thrust was 18.0±7.4% of lift, lift was somewhat higher/equal/lower than body mass in 61.3%, 16.1%, 22.6% of all totally analysable flights (n=31). The following parameters were varied as functions of volume of feeding solution (5–20 l in steps of 5 l) and energy content. (18.5–74.0 J in steps of 18.5 J): total flight time, velocity, total flight distance, mean lift, thrust, mean resultant aerodynamic force, tilting angle, total flight impulse, wingbeat frequency, metabolic power and metabolic power related to body mass, the latter related to empty, full and mean (=100 mg) body mass. The following positive correlations were found: L=1.069·10^-9 f ^2.538; R=1.629·10^-9 f ^2.464; P _m=7.079·10^-8 f ^2.456; P _m=0.008v+0.008; P _m=18.996L+0.022; P _m=19.782R+0.021; P _m=82.143T+0.028; P _m=1.245·bm _f ^1.424 ; P _{mrel e}=6.471·bm _f ^1.040 ; =83.248+0.385. The following negative correlations were found: V=3.939–0.032; T=1.324·10^-4–0.038·10^-4. Statistically significant correlations were not found in T(f), L(), R(), f(), P _m(bm _e), P _{m rel e}(bm _e), P _{m rel f}(bm _e), P _{m rel f}(bm _f).Abbreviations A(m²) frontal area - bl(m) body length - bm(mg) body mass - c(mol·1^-1) glucose concentration of feeding solution - c _D (dimensionless) drag coefficient, related to A - D(N) drag - F _w(N) body weight - F _wp weight of paper fragment lost at flight start - f wingbeat frequency (s^-1) - g(=9.81 m·s^-2) gravitational acceleration - I(Ns)=R(t) dt total impulse of a flight - L(N) lift vertical sustaining force component - P _m(J·s^-1=W) metabolic power - P_{m ret} (W·g^-1) metabolic power, related to body mass - R(N) resultant aerodynamic force - Re v·bl·v ^-1 (dimensionless) Reynolds number, related to body length - s(m) v(t) dt virtual flight distance of a flight - s(km) total virtual flight distance - T (N) thrust horizontal force component of horizontal flight - T _a (°C) ambient temperature - t(s) time - t _tot (s or min) total flight time - v(m·s^-1) flight velocity - v(l) volume of feeding solution - W (J) energy and energy content of V - ( °) body angle of attack between body longitudinal axis and flow direction - ( °) tilting angle ( 90°) between R and the horizont in horizontal flight v(=1.53·10^-5m²·s^-1 for air at 25°) kinematic viscosity - (=1.2 kg·m^-3 at 25°C) air density     

Sodium chloride absorption across the ileal epithelium of the lizardGallotia galloti

Summary Ion transport processes in the ileum of the lizard,Gallotia (=Lacerta) galloti was examined in vitro by measuring Na²² and Cl³⁶ fluxes across short-circuited preparations.In Ringer-bicarbonate solution there was both a net sodium flux ( ) and a net chloride flux ( ) from mucosa to serosa. The inequality between and short-circuit current (I _sc) suggests that part of the net sodium transport is the result of an electrically neutral transport mechanism or that another electrogenic mechanism opposite in sign is contributing to the short-circuit current.In the absence of sodium, the short-circuit current and net chloride flux were abolished. In the absence of chloride, the net sodium was reduced but not abolished and the short-circuit current was unchanged.From an analysis of the effects of the inhibitors furosemide, amiloride, disulfonic stilbene (DIDS) and acetazolamide, a plausible model was developed to explain the characteristics of these transports. It is proposed that the entry of sodium into the cell across the luminal membrane occurs by two pathways. Part occurs by the antiport Na⁺H⁺ and part by an electrogenic pathway. The entry of chloride is by the antiport Cl^–HCO ₃ ^– .Symbols and abbreviations DIDS 4,4 diisothiocyanatostilbene-2,2-disulfonic acid - G _t tissue conductance - I _sc short circuit current - m mucosal - PD potential difference - s serosal     

Severe hypoxia decreases oxygen uptake relative to intensity during submaximal graded exercise

The effect of severe acute hypoxia (fractional concentration of inspired oxygen equalled 0.104) was studied in nine male subjects performing an incremental exercise test. For power outputs over 125 W, all the subjects in a state of hypoxia showed a decrease in oxygen consumption ( O₂) relative to exercise intensity compared with normoxia (P < 0.05). This would suggest an increased anaerobic metabolism as an energy source during hypoxic exercise. During submaximal exercise, for a given O₂, higher blood lactate concentrations were found in hypoxia than in normoxia (P < 0.05). In consequence, the onset of blood lactate accumulation (OBLA) was shifted to a lower O₂ ( O₂ 1.77 l·min^–1 in hypoxia vs 3.10 l·min^–1 in normoxia). Lactate concentration increases relative to minute ventilation ( _E) responses were significantly higher during hypoxia than in normoxia (P < 0.05). At OBLA, _E during hypoxia was 25% lower than in the normoxic test. This study would suggest that in hypoxia subjects are able to use an increased anaerobic metabolism to maintain exercise performance.     

On the appropriateness of use of a continuous formulation for the modelling of discrete multireactant systems following Michaëlis–Menten kinetics

The possibility of solving the mass balances to a multiplicity of substrates within a CSTR in the presence of a chemical reaction following Michaelis-Menten kinetics using the assumption that the discrete distribution of said substrates is well approximated by an equivalent continuous distribution on the molecular weight is explored. The applicability of such reasoning is tested with a convenient numerical example. In addition to providing the limiting behavior of the discrete formulation as the number of homologous substrates increases, the continuous formulation yields in general simpler functional forms for the final distribution of substrates than the discrete counterpart due to the recursive nature of the solution in the latter case.List of Symbols C{N. M} mol/m³ concentration of substrate containing N monomer residues each with molecular weight M - {N, M} normalized value of C{N. M} - C {M} mol/m³ da concentration of substrate of molecular weight M - _in normalized value of C {M} at the i-th iteration of a finite difference method - {M} normalized value of C {M} - C ₀{N.M} mol/m³ inlet concentration of substrate containing N monomer residues each with molecular weight M - {N ·M} normalized value of C₀{N. M} - _{0 i} normalized value of C ₀ {M} at the i-th iteration of a finite difference method - C ₀ {M} mol/m³ da initial concentration of substrate of molecular weight M - C _tot mol/m³ (constant) overall concentration of substrates (discrete model) - C _tot mol/m³ (constant) overall concentration of substrates (continuous model) - D deviation of the continuous approach relative to the discrete approach - i dummy integer variable - I arbitrary integration constant - j dummy integer variable - k dummy integer variable - K _m mol/m³ Michaëlis-Menten constant for the substrates - l dummy integer variable - M da molecular weight of substrate - M normalized value of M - M da maximum molecular weight of a reacting substrate - N number of monomer residues of a reacting substrate - N maximum number of monomer residues of a reacting substrate - N total number of increments for the finite difference method - Q m³/s volumetric flow rate of liquid through the reactor - S inert product molecule - S _i substrate containing i monomer residues - V m³ volume of the reactor - v _max mol/m³ s reaction rate under saturating conditions of the enzyme active site with substrate - v _max{N. M} mol/m³ s reaction rate under saturating conditions of the enzyme active site with substrate containing N monomer residues with molecular weight M - _max{N · M} dimensionless value of v_max{N. M} (discrete model) - _max{M} dimensionless value of v _max {M} (continuous model) - mol/m³ s molecular weight-averaged value of v_max (discrete model) - mol.da/m³s molecular weight-averaged value of v_max (continuous model) - v _max {M} mol.da/m³s reaction rate under saturating conditions of the enzyme active site with substrate with molecular weight M - _max {M} dimensionless value of v_max{M} - _{max, (i)} dimensionless value of v_max{M} at the i-th iteration of a finite difference method - v _max mol/m³ s reference constant value of v _max Greek Symbols dimensionless operating parameter (discrete distribution) - dimensionless operating parameter (continuous distribution) - M da (average) molecular weight of a monomeric subunit - M selected increment for the finite difference method - auxiliary corrective factor (discrete model)     

Oxygen controlled batch cultivations of Schizophyllum commune for enhanced production of branched β-1,3-glucans

Oxygen and shear stress are the key factors for enhanced glucan production with Schizophyllum commune. During batch cultivation control of or (specific oxygen uptake rate) was achieved by variation of the impeller speed. Biomass was modelled by using the carbon and oxygen balance derived from exhaust data. At mycel growth a of 0.042 h^–1 presents just the border before oxygen limitation arises and is simultaneously the optimum operation condition for maximum glucan formation. Related to an overall cultivation time of 72 h a maximum of both productivity (4.3 kg m^–3 d^–1) and yield (13 kg m^–3) were obtained.List of Symbols C kg m^–3 concentration - k _L a h ^–1 volume related oxygen transfer coefficient - K _s mol m^–3 substrate saturation constant - N rpm impeller speed - % oxygen partial pressure of the liquid phase - kg m^–3h^–1 oxygen uptake rate - h^–1 specific oxygen uptake rate, kg O₂ (kg biomass h)^–1 - t h time - yield coefficient (biomass formed/oxygen consumed) Greek Symbols h^–1 specific growth rate Indices O ₂ oxygen - X biomass - L liquid phase - * gas/liquid interface - S substrate (glucose) Dedicated to the 65th birthday of Professor Fritz Wagner.This work was kindly supported in parts by B. Braun Biotech International. The authors are grateful to Prof. Dr. Fritz Wagner for scientific support and appreciate the technical assistance of Detlev Rasch