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91.
Reis M. F. Machado A. A. S. C. Abdulla M. Canário J. Silva J. C. 《Biological trace element research》1994,43(1):585-596
Biological Trace Element Research - To make the best use of time and facilities, a neutron activation system, fully automatic, including spectrum and data processing, to be used with short-lived... 相似文献
92.
93.
Nostoc sp. was cultivated in an air-lift reactor with continuous recirculation of the head gas phase that aerated and agitated the cyanobacterial suspension at regulated flow rates. The supply of inorganic carbon for growth was coupled with pH control, in the range of 7.7 to 8.1, by intermittent sparging of CO2-head gas mixtures. The formation of irregular bubbles with swirling motion at the photostage of the reactor promoted efficient CO2 transference in dense populations of Nostoc sp. (1.1 g/l) when bubbling at flow rates of 10 l/min. Biomass productivity was almost six-fold higher in the photoreactor (16.4 mg/l.h) than in a conventional system (2.8 mg/l.h). The exponential growth phase of cultures in the photoreactor amounted to 60% of the total growth period.The authors are with the Laboratorio de Alimentos, Area Microbiologia, Facultad de Quimica Bioquimica y Farmacia, Universidad Nacional de San Luis, Chacabuco y Pedernera, 5700 San Luis, Argentina 相似文献
94.
95.
Zampronio AR Melo MC Silva CA Pelá IR Hopkins SJ Souza GE 《Mediators of inflammation》1994,3(5):365-373
The aim of this study was to investigate the pyrogenic activity of factor(s) released by rat peritoneal macrophages following a brief stimulation with LPS. The effect of this factor on the number of circulating leukocytes and serum Fe, Cu and Zn levels, was also evaluated. The possibility that the content of interleukin (IL)-1beta, IL-6 and tumour necrosis factor (TNF) in the supernatant could explain the observations was investigated. Supernatant produced over a period of 1 h by peritoneal macrophages, following a 30 min incubation with LPS at 37 degrees C, was ultrafiltered through a 10 000 MW cut-off Amicon membrane, sterilized, and concentrated 2.5, 5, 10 and 20 times. The intravenous (i.v.) injection of this supernatant induced a concentration-dependent fever in rats with a maximal response at 2 h. The pyrogenic activity was produced by macrophages elicited with thioglycollate and by resident cells. The supernatants also induced neutrophilia and reduction in Fe and Zn 6 h after the injection. Absence of activity in boiled supernatants, or supernatants from macrophages incubated at 4 degrees C with LPS, indicates that LPS was not responsible for the activity. In vitro treatment with indomethacin (Indo), dexamethasone (Dex), or cycloheximide (Chx) did not modify the release of pyrogenic activity into the supernatant or its effects on the reduction in serum metal levels. Although Chx abolished the production of mediator(s) inducing neutrophilia, and Dex reduced the induction of IL-1beta, TNF and IL-6, injection of the highest concentration of these cytokines detected in the supernatants did not induce fever. In vivo treatment with Dex, but not Indo, abolished the fever induced by the supernatant. These results suggest that macrophages contain pre-formed pyrogenic mediator(s), not related to IL-1beta, IL-6 or TNF, that acts indirectly and independently of prostaglandtn. It also seems likely that the pyrogenic activity is related to the factor responsible for the reduction of serum Fe and Zn levels, but not the neutrophilia. 相似文献
96.
97.
Hydraulic properties of sphagnum peat moss and tuff (scoria) and their potential effects on water availability 总被引:2,自引:0,他引:2
The importance of macrostructure to root growth of ryegrass (L. perenne) seedlings sown on the soil surface was studied in two soils in which the macrostructure had resulted mainly from root growth
and macro-faunal activity. Sets of paired soil cores were used, one of each pair undisturbed and the other ground and repacked
to the field bulk density.
Undisturbed and repacked soils were first compared at equal water potentials in the range −1.9 to −300 kPa. At equal water
potential, the undisturbed soil always had the greater strength (penetration resistance), and root growth was always greater
in the repacked soil with no macrostructure than it was in the soil with macrostructure intact. At equal high strength (low
water potentials) it appeared that root growth was better when soils were structured. When strength was low (high water potentials),
root growth was better in the unstructured soil.
Soils were then compared during drying cycles over 21 days. The average rate at which roots grew to a depth of 60 mm, and
also the final percentage of plants with a root reaching 60 mm depth, was greatest in repacked soils without macrostructure.
The species of vegetation growing in the soil before the experiment affected root growth in undisturbed soil; growth was slower
where annual grasses and white clover had grown compared with soil which had supported a perennial grass.
It appears that relatively few roots locate and grow in the macrostructure. Other roots grow in the matrix, if it is soft
enough to be deformed by roots. Roots in the matrix of a structured soil grow more slowly than roots in structureless soil
of equal bulk density and water potential. The development of macrostructure in an otherwise structureless soil, of the type
studied, is of no advantage to most roots. However, once a macrostructure has developed, the few roots locating suitable macropores
are able to grow at low water potential when soil strength is high. The importance of macrostructure to establishing seedlings
in the field lies in rapid penetration of at least a few roots to a depth that escapes surface drying during seasonal drought.
ei]{gnB E}{fnClothier} 相似文献
98.
Candida tropicalis DSM 7524 was used to produce xylitol from d-xylose. The fermentation conditions were optimized during continuous cultivation. The strain employed showed no great dependence upon temperature in a range between 30° C and 37° C. It achieved its best yield of xylitol from d-xylose at a pH value of 2.5. Such low pH values allow non sterile cultivation, which is a major economic factor. With an oxygen uptake rate of 0.8–1 ml oxygen per litre culture medium, the C. tropicalis produce xylitol at a yield of between 77% and 80% of the theoretical value. Higher yeast extract concentrations prevent the conversion of d-xylose into xylitol. d-xylose acts as a growth inhibitor in higher concentrations. The maximum xylitol yield was reached at a d-xylose concentration of around 100 g/l. In a non sterile batch culture with substrate shift 220 g/l xylitol were produced from 300 g/l d-xylose at a xylitol productivity rate of 0.37 g/(lh). In order to increase the specific yield, C. tropicalis was immobilised on porous glass and cultivated in a fluidized bed reactor. In a continuous non sterile cultivation with immobilised cells 155 g/l d-xylose produced 90–95% g/l xylitol with a productivity of 1.35 g/(lh).Mr. S. S. da Silva was a visiting scientist to the GBF. He was supported by a scholarship from the National Council of Scientific and Technological Development, Brasilia, Brazil (CNPq).We also would like to gratefully acknowledge the support of Prof. Dr. Michele Vitolo of the University of Sao Paulo, and the Centre for Biotechnology and Chemistry, Lorena, S. P. Brazil, in particular the Department of Fermentative Process.We are grateful to Prof. Rainer Jonas, head of the International Cooperation between Germany/Brazil for the helpful discussions and Dr. Heinrich Lönsdorf (GBF) for the Scanning electron micrographs.Dedicated to the 65th birthday of Prof. Dr. Fritz Wagner. 相似文献
99.
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 vmax{N. M} (discrete model)
-
max{M}
dimensionless value of v
max
{M} (continuous model)
-
mol/m3 s
molecular weight-averaged value of vmax (discrete model)
-
mol.da/m3s
molecular weight-averaged value of vmax (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 vmax{M}
-
max, (i)
dimensionless value of vmax{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) 相似文献
100.