Gas-residence time distribution (RTD) response curves measured in a 23 m high pilot plant airlift tower loop reactor, which consisted of a riser, a special downcomer construction and at the top of the riser a large head. The measurements were evaluated by means of a deterministic dispersion model, which yielded the following particular parameters for the riser, downcomer and the head: Gas-Bo numbers, gas-mean residence times, gas holdups, liquid velocities, gas and liquid circulation times as well as a fraction of the large and small bubbles in a model medium (water) and during cultivation of baker's yeast.List of Symbols
A
cross section
-
Bo
Bodenstein number
-
Bod
(= ldwG,d/Dd)
-
Boh
(= lhwG,h/Dh)
-
Bor
(= lrwG,r/Dr)
-
D
longitudinal dispersion coefficient
-
E
gas holdup
-
E(t)
RTD-density function
-
L, l
length parameter
-
q
fraction of the gas throughput which is not recirculated (approximately equal to fraction of the large bubbles)
-
r
fraction of the throughput which is recirculated (approximately equal to the fraction of the small bubbles)
-
tc
circulation time
-
tcL
liquid circulation time
-
tc,L*
liquid circulation time calculated from the measured wLd in the downcomer
-
Vh
hydrodynamical calculated gas-liquid volume
-
Vdh
(=Vd+0.75/2 Vk)
-
Vkh
=(0.25Vk)
-
Vrh
= (Vr+0.75/2 Vk)
-
VL
liquid volume
-
VG
dispersed gas volume
-
VG*
gas throughput at the gas distributor (given in m3/h) under standard conditions, 1 bar and 25°C)
-
VG,d*
gas throughput in downcomer (=VG*
)
-
VG,h*
gas throughput in head (=VG*
)
-
VG,r*
gas throughput in riser (VG*
(1+)
-
wg
gas velocity
-
wG,rel
relative gas velocity with respect to the liquid velocity wL
-
wG,d
gas velocity in the downcomer (=wG,rel–wLd)
-
wG,h
gas velocity in the head (=wG,rel) (since wLh = o)
-
wG,r
gas velocity in the riser (=wG,rel+wLr)
-
wL
liquid velocity
-
wL,d
liquid velocity in the downcomer measured with mass flow meter
-
wsg·wSL
superficial gas and liquid velocities
-
first moment of the response curve
-
mean residence time
Indices
d
downcomer
-
G
gas phase
-
h
head
-
L
liquid phase
-
r
riser
-
h
hydrodynamic (upper position)
Dedicated to the 65th birthday of Proffessor Fritz Wagner.The authors gratefully acknowledge the financial support by the Krupp Industrietechnik, Grevenbroich and the support of Pleser Co, Darmstadt. H. M. Rüffer thanks the Verband der Chemischen Industrie for a Fond der Chemie scholarship, and W. Liwei thanks the government of Lower Saxony for a graduate scholarship. 相似文献
Summary Cystic fibrosis (CF) involves abnormalities in mucus production and secretion of the airway. Studies of the regulation of
airway mucin production and secretion has been difficult due to the lack of in vitro models of the airway epithelial cells
which express functional differentiation. Because the majority of the mucin in the airway is apparently produced by the submucosal
glands, we have focused our attention on the development of cell culture models of human airway submucosal glands. This report
describes the propagation of CF airway submucosal gland epithelial cells which continue to express mucin production. The CF
bronchus was obtained from a 31-yr-old patient who received a double lung transplant. The glands were dissected out and primary
cultures prepared by the explant/outgrowth procedure. The cells were immortalized by infection with Adl2-SV40 hybrid virus.
The cultures are maintained in serum-free keratinocyte basal medium supplemented with insulin (5μg/ml), hydrocortisone (0.5μg/ml), epidermal growth factor (10 ng/ml), bovine pituitary extract (25μg/ml), and antibiotics. Cultures were passaged using 0.125% trypsin in Ca+2 and Mg+2-free Hanks’, balanced salt solution. Polymerase chain reaction (PCR) analysis demonstrated that the cells were homozygous
for the ΔF508 mutation. Morphologic observations showed that the cells were epithelial and were interconnected by sparsely
distributed desmosomes. Their cytoplasm contained secretory-type structures including abundant Golgi, rough endoplasmic reticulum,
and secretory vesicles. Immunofluorescent studies determined that all cells were positive for cytokeratins, mucin glycoconjugates,
and cystic fibrosis transmembrane conductance regulator. The cultures secreted substantial amounts of mucin glycoproteins
and expressed the MUC-2 mucin gene. Patch clamp experiments revealed that the cells expressed defective Cl− channels which were not activated by Forskolin. 相似文献
Human mononuclear cells pre-labeled with [3H]arachidonic acid were shown to release metabolites following in vitro addition of heat-killed Salmonella typhi (HKST). The amount of label released was significantly higher than that seen with live S. typhi (LST). Addition of increasing amounts of HKST resulted in an increased release of metabolites. Enzyme immunoassay of the culture supernatants revealed that the bulk of the metabolite released was prostaglandin E2 (PGE2). Leukotriene B4 (LTB4) and leukotriene C4 (LTC4) were not detectable in the culture supernatants. The significance and implications of these results are discussed. 相似文献
Motivated by investigating the relationship between progesterone and the days in a menstrual cycle in a longitudinal study, we propose a multikink quantile regression model for longitudinal data analysis. It relaxes the linearity condition and assumes different regression forms in different regions of the domain of the threshold covariate. In this paper, we first propose a multikink quantile regression for longitudinal data. Two estimation procedures are proposed to estimate the regression coefficients and the kink points locations: one is a computationally efficient profile estimator under the working independence framework while the other one considers the within-subject correlations by using the unbiased generalized estimation equation approach. The selection consistency of the number of kink points and the asymptotic normality of two proposed estimators are established. Second, we construct a rank score test based on partial subgradients for the existence of the kink effect in longitudinal studies. Both the null distribution and the local alternative distribution of the test statistic have been derived. Simulation studies show that the proposed methods have excellent finite sample performance. In the application to the longitudinal progesterone data, we identify two kink points in the progesterone curves over different quantiles and observe that the progesterone level remains stable before the day of ovulation, then increases quickly in 5 to 6 days after ovulation and then changes to stable again or drops slightly. 相似文献
Continuous cropping (CC) obstacle is a major threat in legume crops production; however, the underlying mechanisms concerning the roles allelochemicals play in CC obstacle are poorly understood. The current 2-year study was conducted to investigate the effects of different kinds and concentrations of allelochemicals, p-hydroxybenzoic acid (H), cinnamic acid (C), phthalic acid (P), and their mixtures (M) on peanut root growth and productivity in response to CC obstacle. Treatment with H, C, P, and M significantly decreased the plant height, dry weight of the leaves and stems, number of branches, and length of the lateral stem compared with control. Exogenous application of H, C, P, and M inhibited the peanut root growth as indicated by the decreased root morphological characters. The allelochemicals also induced the cell membrane oxidation even though the antioxidant enzymes activities were significantly increased in peanut roots. Meanwhile, treatment with H, C, P, and M reduced the contents of total soluble sugar and total soluble protein. Analysis of ATPase activity, nitrate reductase activity, and root system activity revealed that the inhibition effects of allelochemicals on peanut roots might be due to the decrease in activities of ATPase and NR, and the inhibition of root system. Consequently, allelochemicals significantly decreased the pod yield of peanut compared with control. Our results demonstrate that allelochemicals play a dominant role in CC obstacle-induced peanut growth inhibition and yield reduction through damaging the root antioxidant system, unbalancing the osmolytes accumulation, and decreasing the activities of root-related enzymes.
Salinity impairs plant growth and development, thereby leading to low yield and inferior quality of crops. Nitric oxide (NO) has emerged as an essential signaling molecule that is involved in regulating various physiological and biochemical processes in plants. In this study, tomato seedlings of Lycopersicum esculentum L. “Micro-Tom” treated with 150 mM sodium chloride (NaCl) conducted decreased plant height, total root length, and leaf area by 25.43%, 24.87%, and 33.67%, respectively. While nitrosoglutathione (GSNO) pretreatment ameliorated salt toxicity in a dose-dependent manner and 10 µM GSNO exhibited the most significant mitigation effect. It increased the plant height, total root length, and leaf area of tomato seedlings, which was 31.44%, 20.56%, and 51.21% higher than NaCl treatment alone, respectively. However, NO scavenger 2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide potassium (cPTIO) treatment reversed the positive effect of NO under salt stress, implying that NO is essential for the enhancement of salt tolerance. Additionally, NaCl?+?GSNO treatment effectively decreased O2? production and H2O2 content, increased the levels of soluble sugar, glycinebetaine, proline, and chlorophyll, and enhanced the activities of antioxidant enzymes and the content of antioxidants in tomato seedlings in comparison with NaCl treatment, whereas NaCl?+?cPTIO treatment significantly reversed the effect of NO under salt stress. Moreover, we found that GSNO treatment increased endogenous NO content, S-nitrosoglutathione reductase (GSNOR) activity, GSNOR expression and total S-nitrosylated level, and decreased S-nitrosothiol (SNO) content under salt stress, implicating that S-nitrosylation might be involved in NO-enhanced salt tolerance in tomatoes. Altogether, these results suggest that NO confers salt tolerance in tomato seedlings probably by the promotion of photosynthesis and osmotic balance, the enhancement of antioxidant capability and the increase of protein S-nitrosylation levels.