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1.
The ethanol-inhibitory behaviour of the yeast Saccharomyces cerevisiae Sc 5 was found to be characterized by a continual-linear relation between the specific ethanol formation rate and the ethanol concentration. Therefore the simple equation could be applied for it. It is shown that this model is correct only then, if all of the process parameters are in their optimum. Out of the optimum temperature range the characteristics of the function ν = f(P) change in such a way that in regard to the ethanol concentration P twc linear relations exist for each suboptimum temperature: and a non-linear equation is current for each superoptimum temperature: where bT is also a function of the temperature and always less than 1. Taking as a basis these equations the specific ethanol formation rate of the used strain can be calculated for the whole biokinetic P/T-sphere of ethanol production. 相似文献
2.
Influence of internal loading on phosphorus concentration in shallow lakes before and after reduction of the external loading 总被引:2,自引:1,他引:1
An analysis of data from 49 shallow lakes showed, that the parameters of empirical models between phosphorus loading and concentration in the lake (e.g. Vollenweider type of relations) differ significantly for lakes without or with a reduced external loading. For lakes without a reduction of the external loading the summer phosphorus concentration is determined by the external phosphorus loading and the hydraulic loading. For these lakes the classical models suffice; deviations between calculations and measurements are partly due to errors made in the determination of the loading.In contrast, for lakes where the external loading was reduced, the measured internal loading explains most of the variation in the summer lake concentration. The external loading is of minor importance and the classical models cannot be applied. The internal loading measured before reduction of the external loading is not useful in predicting the concentration afterwards. Instead of the internal loading, the sediment composition can be used. The advantage of using sediment composition is that these variables are easier to determine and vary less in time. The most promising variable is the ratio between total P and total Fe in the sediment.Abbreviations: Qs
hydraulic loading (m y-1)
-
hydraulic retention time (y)
- Lext
external phosphorus loading (gP m-2 y-1)
- Lint
internal phosphorus loading (gP m-2 y-1)
- Plake
phosphorus concentration in the lake (gP m-3)
- Pinlet
phosphorus concentration in the inlet water (gP m-3)
- Psed
phosphorus content on the sediment (gP kg-1 d.w.)
- Fesed
iron content of the sediment (gFe kg-1 d.w.)
-
Y
dependent variable multiple regression calculations
-
X1, X2
independent variables multiple regressions calculations
-
a, a1
constants
-
a2, b
constants 相似文献
3.
Robert A. Scherrer 《化学与生物多样性》2009,6(11):1917-1922
A number of membrane‐permeation models require the incorporation of an unstirred or unstirrable water layer (UWL). An example occurs in PAMPA models when the effective permeation rate of lipophilic acids and bases, Pe, falls behind the expected permeation rate, Pm, at pH values providing a high concentration of unionized species in the donor phase. In such cases, the compound has an apparent pKa of a weaker acid or base. The explanation is that an UWL adjacent to the membrane provides a rate‐limiting diffusion barrier for such compounds. The thickness of the UWL is correlated with the difference between the aqueous pKa and the apparent pKa (pK ). Here, we provide an explanation for the pK term that requires no UWL. It comes from the fact that, in the process of passing into a membrane, an ionizable compound undergoes a change in pKa. At some point along its path into the membrane, the compound attains a maximum free energy, at which point it is as likely to continue into the membrane, as it is to return to the donor phase. This is the transition state for absorption. The pK is the pKa of the compound at the transition state. This is a testable hypothesis (see text). The relevance of absorption to permeation depends on the rate‐limiting step of permeation. 相似文献
4.
The influence of phosphorus (P) and nitrogen (N) supply on biomass, leaf area, photon saturated photosynthetic rate (Pmax), quantum yield efficiency (), intercellular CO2 concentration (Ci), and carboxylation efficiency (CE) was investigated in Vicia faba. The influence of P on N accumulation, biomass, and leaf area production was also investigated. An increase in P supply was consistently associated with an increase in N accumulation and N productivity in terms of biomass and leaf area production. Furthermore, P increased the photosynthetic N use efficiency (NUE) in terms of Pmax and . An increase in P supply was also associated with an increase in CE and a decrease in Ci. Under variable daily meteorological conditions specific leaf nitrogen content (NL), specific leaf phosphorus content (PL), specific leaf area (L), root mass fraction (Rf), Pmax, and remained constant for a given N and P supply. A monotonic decline in the steady-state value of Rf occurred with increasing N supply. L increased with increasing N supply or with increasing NL. We tested also the hypothesis that P supply positively affects both N demand and photosynthetic NUE by influencing the upper limit of the asymptotic values for Pmax and CE, and the lower limit for Ci in response to increasing N.This revised version was published online in March 2005 with corrections to the page numbers. 相似文献
5.
Accuracy of the AVHRR vegetation index as a predictor of biomass,primary productivity and net CO2 flux 总被引:5,自引:0,他引:5
The Normalized Difference Vegetation Index (NDVI) or greenness index, based on the Advanced Very High Resolution Radiometer (AVHRR) aboard the NOAA-7 satellite, has been widely interpreted as a measure of regional to global vegetation patterns. This study provides the first rigorous, quantitative evaluation of global relationships between the NDVI and geographically representative vegetation data-bases, including field metabolic measurements and carbon-balance results from global simulation models. Geographic reliability of the NDVI is judged by comparing NDVI values for different surface types with a general global trend and by statistical analysis of relationships to biomass amounts, net and gross primary productivity, and actual evapotranspiration. NDVI data appear to be relatively reliable predictors of primary productivity except in areas of complex terrain, for seasonal values at high latitudes, and in extreme deserts. The strength of the NDVI-productivity relationship seems comparable to that of earlier climate-based productivity models. Little consistent relationship was found, across different vegetation types, between NDVI and biomass amounts or net biospheric CO2 flux.Abbreviations AET=
Actual Evapotranspiration
- AVHRR=
Advanced Very High Resolution Radiometer
- GPP=
Gross Primary Production
- GVI=
Global Vegetation Index
- NDVI=
Normalized Difference Vegetation Index
- NPP=
Net Primary Production 相似文献
6.
Kosei Shioji Takafumi Ueyama Nobuaki Ueda Emiko Mutoh Tsutomu Kurisaki Hisanobu Wakita Kentaro Okuma 《Journal of Molecular Catalysis .B, Enzymatic》2008,55(3-4):146-151
The lipase-catalyzed optical resolution of 2-, 3-, and 5-hydroxyalkyl phosphorus compounds 1 provided the corresponding optically pure diastereomers in good yields. (SP, R)- and (RP, S)-1 were acylated faster than (SP, S)- and (RP, R)-1. The stereoselectivity at the phosphorus atom changed with the flexibility of the active sites in the lipases. The stereoselectivity at the phosphorus atom was higher in the reaction of 1a than in the reaction of 1b,c. The reaction rate of -hydroxyalkylphosphine oxide 1c was faster than that of 1a, although less enantioselectivity was observed at the phosphorus atom. 相似文献
7.
Summary To assess steady-state transepithelial osmotic water permeability (P
f
), rabbit proximal convoluted tubules were perfused in vitro with the impermeant salt, sodium isethionate at 26°C. Osmotic gradients () were established by varying the bath concentration of the impermeant solute, raffinose. When lumen osmolality was 300 mOsm and bath osmolality was 320, 360 and 400 mOsm, apparentP
f
decreased from 0.5 to 0.10 to 0.08 cm/sec, respectively. Similar data were obtained when lumen osmolality was 400 mOsm. Five possible causes of the dependence of apparentP
f
were considered experimentally and/or theoretically: (1) external unstirred layer (USL); (2) cytoplasmic USL; (3) change in surface area; (4) saturation of water transport; (5) down-regulation ofP
f
. ApparentP
f
was inhibited 83% byp-chloromercuribenzene sulfonate (pCMBS) at 20 mOsm, but not at 60 mOsm , suggesting presence of a serial barrier resistance to water transport. Increases in perfusate or bath solution flow rate and viscosity did not alter apparentP
f
, ruling out an external USL. A simple cytoplasmic USL, described by a constant USL thickness and solute diffusion coefficient, could not account for the dependence of apparentP
f
according to a mathematical model. The activation energy (E
a
) for apparentP
f
increased from 7.0 to 12.5 kcal/mol when was increased from 20 to 60 mOsm, not consistent with a simple USL or a change in membrane surface area with transepithelial water flow. These findings are most consistent with a complex cytoplasmic USL, where the average solute diffusion coefficient and/or the area available for osmosis decrease with increasing . These results (1) indicate that trueP
f
(at physiologically low ) is very high (>0.5 cm/sec) in the rabbit proximal tubule; (2) provide an explanation for the wide variation inP
f
values reported in the literature using different , and (3) suggest the presence of a flow-dependent cytoplasmic barrier to water flow. 相似文献
8.
Debashis Kushary 《Biometrical journal. Biometrische Zeitschrift》1996,38(7):865-878
Let x1 ≤x2 ≤x3 … ≤xr be the r smallest observations out of n observations from a location-scale family with density $ \frac{1}{\sigma}f\left({\frac{{x - \mu}}{\sigma}} \right) $ where μ and σ are the location and the scale parameters respectively. The goal is to construct a prediction interval of the form $ \left({\hat \mu + k_1 \hat \sigma,\,\hat \mu + k_2 \hat \sigma} \right) $ for a location-scale invariant function, T(Y) = T(Y1, …, Ym), of m future observations from the same distribution. Given any invariant estimators $ \hat \mu $ and $ \hat \sigma $, we have developed a general procedure for how to compute the values of k1 and k2. The two attractive features of the procedure are that it does not require any distributional knowledge of the joint distribution of the estimators beyond their first two raw moments and $ \hat \mu $ and $ \hat \sigma $ can be any invariant estimators of μ and σ. Examples with real data have been given and extensive simulation study showing the performance of the procedure is also offered. 相似文献
9.
K. Richter 《Engineering in Life Science》1986,6(3):239-243
The ethanol tolerance behaviour of the strain Saccharomyces cerevisiae Sc 5 regarding the growth is characterized by a threshold ethanol inhibitory concentration (P1' = 42.5 g/l) and a linear relationship between the specific growth rate and the ethanol concentration within the limits P1' < P < P′. The maximum ethanol concentration for growth amounts to P′ = 84 g/l. A general model for the inhibition of growth and alcohol production, respectively, caused by ethanol, is deduced from experimental and bibliographical data: If the inhibitory effects are linear, the exponents b, b' become 1. 相似文献
10.
Antarctic emerald rockcod have the capacity to compensate for warming when uncoupled from CO2‐acidification
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Brittany E. Davis Erin E. Flynn Nathan A. Miller Frederick A. Nelson Nann A. Fangue Anne E. Todgham 《Global Change Biology》2018,24(2):e655-e670
Increases in atmospheric CO2 levels and associated ocean changes are expected to have dramatic impacts on marine ecosystems. Although the Southern Ocean is experiencing some of the fastest rates of change, few studies have explored how Antarctic fishes may be affected by co‐occurring ocean changes, and even fewer have examined early life stages. To date, no studies have characterized potential trade‐offs in physiology and behavior in response to projected multiple climate change stressors (ocean acidification and warming) on Antarctic fishes. We exposed juvenile emerald rockcod Trematomus bernacchii to three PCO2 treatments (~450, ~850, and ~1,200 μatm PCO2) at two temperatures (?1 or 2°C). After 2, 7, 14, and 28 days, metrics of physiological performance including cardiorespiratory function (heart rate [fH] and ventilation rate [fV]), metabolic rate (), and cellular enzyme activity were measured. Behavioral responses, including scototaxis, activity, exploration, and escape response were assessed after 7 and 14 days. Elevated PCO2 independently had little impact on either physiology or behavior in juvenile rockcod, whereas warming resulted in significant changes across acclimation time. After 14 days, fH, fV and significantly increased with warming, but not with elevated PCO2. Increased physiological costs were accompanied by behavioral alterations including increased dark zone preference up to 14%, reduced activity by 12%, as well as reduced escape time suggesting potential trade‐offs in energetics. After 28 days, juvenile rockcod demonstrated a degree of temperature compensation as fV, , and cellular metabolism significantly decreased following the peak at 14 days; however, temperature compensation was only evident in the absence of elevated PCO2. Sustained increases in fV and after 28 days exposure to elevated PCO2 indicate additive (fV) and synergistic () interactions occurred in combination with warming. Stressor‐induced energetic trade‐offs in physiology and behavior may be an important mechanism leading to vulnerability of Antarctic fishes to future ocean change. 相似文献
11.
Summary Water transport mechanisms in rabbit proximal convoluted cell membranes were examined by measurement of: (1) osmotic (P
f
) and diffusional (P
d
) water permeabilities, (2) inhibition ofP
f
by mercurials, and (3) activation energies (E
a
) forP
f
.P
f
was measured in PCT brush border (BBMV) and basolateral membrane (BLMV) vesicles, and in viable PCT cells by stopped-flow light scattering;P
d
was measured in PCT cells by proton NMR Ti relaxation times using Mn as a paramagnetic quencher. In BLMV,P
f
(0.019 cm/sec, 23°C) was inhibited 65% by 5mm
pCMBS and 75% by 300 m HgCl2 (K
l
=42 m);E
a
increased from 3.6 to 7.6 kcal/mole (15–40°C) with 300 m HgCl2. In BBMV,P
f
(0.073 cm/sec, 23°C,E
a
=2.8 kcal/mole, <33°C and 13.7 kcal/mole, >33°C) was inhibited 65% with HgCl2 withE
a
=9.4 kcal/mole (15–45°C). Mercurial inhibition in BLMV and BBMV was reversed with 10 m mercaptoethanol. Viable PCT cells were isolated from renal cortex by Dounce homogenization and differential seiving. Impedence sizing studies show that PCT cells are perfect osmometers (100–1000 mOsm). Assuming a cell surface-to-volume ratio of 25,000 cm–1,P
f
was 0.010±0.002 cm/sec (37°C) andP
d
was 0.0032 cm/sec.P
f
was independent of osmotic gradient size (25–1000 mOsm) withE
a
2.5 kcal/mole (<27°C) and 12.7 kcal/mole (>27°C). CellP
f
was inhibited 53% by 300 m HgCl2 (23°C) withE
a
6.2 kcal/mole. These findings indicate that cellP
f
is not restricted by extracellular or cytoplasmic unstirred layers and that cellP
f
is not flow-dependent. The high BLMV and BBMVP
f
, inhibition by HgCl2, lowE
a
which increases with inhibition, and the measuredP
f
/P
d
>1 in cells in the absence of unstirred layers provide strong evidence for the existence of water channels in proximal tubule brush border and basolateral membranes. These channels are similar to those found in erythrocytes and are likely required for rapid PCT transcellular water flow. 相似文献
12.
U. Hanauer-Thieser W. Nachtigall 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1995,165(6):471-483
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
- Pm 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 相似文献
13.
This study examines the impacts of woody, N2-fixing invasive Acacia spp. on the patterns of nutrient cycling in two invaded ecosystems of differing nutrient status in the Cape floristic region. Patterns of soil nutrient mineralization were measured by a field incubation method while the significance of the fixation process in altering nutrient cycling was assessed by the 15N natural abundance technique. The results confirm earlier reports that invasion by woody shrubs results in organic matter and nutrient enrichment of surface soils of both ecosystems. However, patterns of nutrient availability (phosphorus and nitrogen) were not necessarily enhanced. In the more fertile strandveld both phosphorus and nitrogen (significant at P<0.10) showed trends towards enhanced annual mineralization rates upon invasion, while in the low nutrient fynbos system only phosphorus followed this trend. It is unclear whether this differential response is a consequence of plant- or soil-derived feedbacks on the decomposition processes in each system. The 15N values of the soils from the invaded sites of both ecosystems indicated a strong influence of the alien species on the soil nitrogen component. However, as with other studies of natural ecosystems, the contribution of nitrogen from fixation could not be readily quantified with the 15N natural abundance method because of problems in selecting suitable non-N2-fixing reference plants. A technique of disrupting nodule structure and function, by fumigation with O2, to obtain the 15N value of a non-N2-fixing speciment of the study species was tried and found to overcome some of the problems associated with the lack of suitable reference plants. With this technique it was possible to detect the almost total dependence of A. saligna on N2-fixation in the fynbos soils with their low nitrogen mineralization rates. In the strandveld ecosystem with much higher soil nitrogen release rates A. cyclops was only partly dependent on fixation (about half) for its nitrogen. The nutrient enrichment of both ecosystems and trends towards enhanced rates of nutrient mineralization could have profound implications on the long-term success of alien invader clearing operations and the restoration of the indigenous flora at these sites. 相似文献
14.
In two carp ponds with a long water residence time, the seasonal changes in concentration and internal mass-flow of inorganic nutrients have been estimated together with oxygen production PN of phytoplankton and community respiration. The results were compared with the findings from laboratory microcosms (LM) with a high recycle rate between a) euphotic and b) aphotic + sediment compartment. In the LM's, a dark period of at least 12 hours was necessary for optimum remobilization of CO2, PO− and NH. Very high values of PN were measured even if external nutrient sources were missing. Low nutrient concentrations could be compensated by high vertical fluxes. A cycle of nocturnal mixing and of thermal stratification with anoxia at the mud water interface which increases nutrient regeneration seems to be the principal mechanism which maintains very high PN in hypertrophic shallow waters. 相似文献
15.
The basic relations between the molar fractions and the scanning calorimetry data for the system that includes self-dissociation/association process such as are presented, where mi is the stoichiometric coefficient of the ith state Ai. The relations are described for each state j as where fj(T) is the molar fraction function of state j and ΔHj(T) is the difference enthalpy function of the system referred to the state j, which can be obtained by scanning calorimetry; R is the gas constant; and T is the absolute temperature. By these relations, scanning calorimetry data can be deconvoluted in order to determine the thermodynamic functions by means of single and double deconvolution. The concentration dependence of the data is analyzed by a method presented in this paper. The nonlinear least squares fitting method for the determination of the functions is discussed. For an example of the application of this method to the actual scanning calorimetry data, thermodynamic data of multistate thermal transition of Vibrio parahaemolyticus hemolysin are analyzed. 相似文献
16.
The alcoholic fermentation of grape juice by a wine yeast was studied batchwise at pH 3.6 and 4.05 to develop kinetic equations relating cell concentration, N, to product concentration, P. In the exponential growth phase where A, B, and C are constants, and μ is the specific growth rate. In the stationary phase, where the cell population is constant, was found to apply. This equation, which incorporates a stoichiometric constant, Pm, predicted correctly the operation of a continuous fermentor at pH 3.6 and at 4.05. To study more fully the effect of alcohol concentration on yeast growth, a continuous fermentor was used in which the grape juice feed was supplemented with pure alcohol. At pH 3.6 the specific growth rate varied as, There was no growth inhibition below an alcohol concentration of 2.6 g./100 cc., but inhibition was complete above 6.85 g./100 cc. This is a modified form of the relation suggested by Hinshelwood.1 The data suggest that growth in batch culture was limited not only by alcohol but also by some other factor, probably a nutritional deficiency. 相似文献
17.
Wen‐Liang Hung 《Biometrical journal. Biometrische Zeitschrift》2000,42(4):501-510
In this article, we consider r observations from a non‐homogeneous censored Markov chain, with transition probability matrix P. For the product estimator of P proposed by Aalen and Johansen (1978) and Phelan (1988), we investigate the behavior of Bayesian bootstrap clones to approximate the sampling distribution of , and then construct approximate confidence interval. It is shown that the approximation based on the random‐weighted distribution is first‐order consistent. The performance of the Bayesian bootstrap clones (BBC) is also discussed by small sample simulation. Finally, we illustrate the BBC procedure in the application to the WHO malaria survey data (cf. Singer and Cohen 1970). 相似文献
18.
Summary The osmotic water permeabilityP
f of brush border (BBM) and basolateral (BLM) membrane vesicles from rat small intestine and renal cortex was studied by means of stopped-flow spectrophotometry. Scattered light intensity was used to follow vesicular volume changes upon osmotic perturbation with hypertonic mannitol solutions. A theoretical analysis of the relationship of scattered light intensity and vesicular volume justified a simple exponential approximation of the change in scattered light intensity. The rate constants extracted from fits to an exponential function were proportional to the final medium osmolarity as predicted by theory. For intestinal membranes, computer analysis of optical responses fitted well with a single-exponential treatment. For renal membranes a double-exponential treatment was needed, implying two distinct vesicle populations.P
f values for BBM and BLM preparations of small intestine were equal and amount to 60 m/sec. For renal preparations,P
f values amount to 600 m/sec for the fast component, BBM as well as BLM, and to 50 (BBM) and 99 (BLM) m/sec for the slow component. The apparent activation energy for water permeation in intestinal membranes was 13.3±0.6 and in renal membranes, 1.0±0.3 kCal/mole, between 25 and 35°C. The mercurial sulfhydryl reagentpCMBS inhibited completely and reversibly the highP
f value in renal brush border preparations. These observations suggest that in intestinal membranes water moves through the lipid matrix but that in renal plasma membranes water channels may be involved. From the highP
f values of renal membrane vesicles a transcellular water permeability for proximal tubules can be calculated which amounts to 1 cm/sec. This value allows for an entirely transcellular route for water flow during volume reabsorption. 相似文献
19.
I. V. K. Subrahmanya Sastry G. Pavan Kumar M. Chidambaram 《Bioprocess and biosystems engineering》1994,10(3):127-130
The effect of time delay in specific growth rate () on the periodic operation of bioreactors with input multiplicities is theoretically analyzed for productivity improvement. A periodic rectangular pulse is applied either in feed substrate concentration (Sf) or in dilution rate (D). Periodic operation under feed substrate concentration cycling gives improvement in productivity at lower value of ¯Sf of the two steady-state multiplicities of Sf only when the time delay in is larger. Whereas the larger value of ¯Sf gives improvement in average productivity for all values of time delay. Dilution rate (D) cycling gives an improvement in average productivity particularly for larger time delay in . This improvement in average productivity is obtained only at smaller value of dilution rate out of the two steady-state input multiplicities of D.List of Symbols D 1/h
dilution rate
- F
memory function
- g
dummy variable
- Ki g/l
substrate inhibition constant
- Km g/l
substrate saturation constant
- P g/l
product concentration
- Pm g/l
product saturation constant
- Q g/(hl)
product cell produced per unit time
- S g/l
substrate concentration
- Sf g/l
feed substrate concentration
- Sf,p g/l
feed substrate concentration during fraction of a period
- X g/l
biomass concentration
- YX/S g/g
cell mass yield
- w
variable either S or Z
- Z g/l
weighted average of substrate concentration
Greek Letters
1/h
time delay parameter
-
1
,
2
product yield parameters, g/g and 1/h
-
pulse width expressed as a fraction of a period
-
1/h
specific growth rate
-
m 1/h
maximum specific growth rate
- h
period of oscillation
- –
average value 相似文献
20.
The buoyant densities of natural and synthetic DNA's can be accurately interrelated if second-neighbor influences are taken into account. We derive the following expressions, based partly on the buoyant densities of six synthetic DNA's, for the buoyant densities ρ (g/cm3) of DNA's having random sequences. In CsCl, and in Cs2SO4, . In these equations, HG is the mole fraction of G : C base pairs in the DNA and the buoyant densities are calculated relative to densities for E. coli DNA of 1.703 and 1.426 (g/cm3) in CsCl and Cs2SO4, respectively. 相似文献