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1.
The slow rate of demixing is a major limitation in wide commercial exploitation of aqueous two-phase systems. In the present work, use of a microwave field has been explored for the first time to enhance phase demixing rates (decrease demixing times) of these systems. The microwave-field-assisted demixing process decreased the demixing time by about 2- to 4-fold in a polyethylene glycol/potassium phosphate system and by about 1.5- to 6.5-fold in a polyethylene glycol/maltodextrin system. The enhanced demixing rate can be explained by the dipole rotation, electrophoretic migration of free salts, multiple reflections at the interfaces, droplet-droplet collision, and reduced viscosity of the continuous phase that occur during the application of a microwave field. 相似文献
2.
Aqueous two-phase extraction has been recognized as a versatile downstream processing technique for the recovery of biomolecules. A major deterrent to its industrial exploitation is the slow demixing of the two aqueous phases after extraction, due to their similar physical properties. A method to decrease the demixing times of these systems, employing a travelling acoustic wave field, is reported. The effects of phase composition and microbial cells on demixing in a polyethylene glycol/potassium phosphate two-phase system are studied in detail. As phase composition increased, demixing time decreased gradually. Phase volume ratio was found to have a significant effect on demixing time at low phase compositions. However, at intermediate and high phase compositions, only a small effect on demixing time was observed. The effect of phase composition and volume ratio on demixing behavior was explained based on the droplet size of the dispersed phase, which is the resultant effect of the physical properties of the phases. At all the phase compositions studied, the acoustically assisted process decreased the demixing time by 17-60% when compared to demixing under gravity alone. Increasing the cell concentration increased the demixing time markedly in case of yeast cells. However, it remained practically constant in the case of Lactobacillus casei cells. Application of an acoustic field reduced the demixing times up to 60% and 40% in the case of yeast and L. casei cells, respectively. Visual observations indicated that ultrasonication caused mild circulation currents in the phase dispersion enhancing droplet-droplet interaction, which in turn enhanced the rate of coalescence, eventually resulting in an enhanced demixing rate. 相似文献
3.
Stability of oil-in-water emulsions during freezing and thawing is regulated by the phase transitions occurring in the continuous
and dispersed phases upon thermal treatments and by the composition of the interfacial membrane. In the present study, the
impact of the water phase formulation (0–2.5–5–10–20–30–40% w/w sucrose), the interfacial composition [whey protein isolates (WPI) or sodium caseinate (NaCas) used at different concentrations],
and the particle size on the stability of hydrogenated palm kernel oil (30% w/w)-in-water systems was investigated. Phase/state behaviour of the continuous and dispersed phases and emulsion destabilisation
were studied by differential scanning calorimetry. System morphology was observed by particle size analysis and optical microscopy.
The presence of sucrose in the aqueous phase and reduced particle size distribution significantly improved emulsion stability.
WPI showed better stabilising properties than NaCas at lipid to protein ratios of 10:1, 7.5:1, 5:1 and 4:1. Increased WPI
concentration significantly improved emulsion resistance to breakdown during freeze–thaw cycling. NaCas showed poor stabilising
properties and was ineffective in reducing emulsion destabilisation at 0% sucrose at all the lipid to protein ratios. 相似文献
4.
The phase separation behavior of whey protein isolate (WPI) aggregates and κ-carrageenan (κ-car) mixtures was studied using
the Vrij's theory and image analysis method. The intrinsic parameter (molecular mass and radius of gyration) for κ-car and
the WPI aggregates was determined using intrinsic viscosity and reduced viscosity of each biopolymer. Confocal microscopy
observations revealed the appearance of protein aggregate domains when phase separation occurred, with microgel droplets of
WPI included in a continuous κ-car phase. The occurrence of aggregate droplet has not been reported before for the phase-separating
WPI/κ-car mixtures. So far, network emulsion-like microstructures have been observed with WPI in a network structure. By using
different WPI concentrations (4% or 6%), the microstructure of the systems changes while increasing the κ-car concentration.
The size of the microgels (1–2.5 μm) depends on both κ-car and WPI concentration. Confocal microscopy combined with image
analysis (method of the variance) was used effectively as objective means to determine the phase boundary of the phase-separating
systems. Additional information on the depletion layer thickness, Δ, was obtained using self-consistent field theory. The
results show that Δ has a constant value of 80.5 nm for
ck - car \prec 2 g/l {{\hbox{c}}_{\kappa {\rm{ - car}}}} \prec {\hbox{2 g}}/{l} , in agreement with ∆ ≈ R
g (radius of gyration). Above this concentration, Δ decreases as a function of κ-car concentration. The experimental phase
boundary was well predicted using Vrij's theory. This work showed a new approach to generate phase diagrams (e.g., under shear)
of phase-separating systems. 相似文献
5.
Acoustic demixing of aqueous two-phase systems 总被引:1,自引:0,他引:1
Srinivas ND Barhate RS Raghavarao KS Todd P 《Applied microbiology and biotechnology》2000,53(6):650-654
Aqueous two-phase systems demix slowly due to similar physical properties. This is one of the major drawbacks for their adaptation
for industrial scale extraction of enzymes. In the present work, a method to accelerate the demixing rates of these systems,
employing a traveling acoustic wave field is reported for the first time. Phase-demixing for three systems, viz. polyethylene
glycol (PEG)/sodium sulfate, PEG/potassium phosphate and PEG/maltodextrin were studied. The acoustically assisted process
decreased the demixing time significantly (about 2- to 3-fold in PEG/salt systems and about 2-fold in the PEG/maltodextrin
system), compared to that in gravity alone. Ultrasonication apparently enhanced the coalescence of the dispersed phase droplets
due to the mild circulation currents it caused in the dispersion. This in turn enhanced the rate of demixing due to the increased
migration velocity of the larger droplets.
Received: 3 November 1999 / Received revision: 10 January 2000 / Accepted: 14 January 2000 相似文献
6.
The salinity tolerance of aRhizobium meliloti strain isolated from salt-affected soils was examined. Growth of the strain on yeast—mannitol broth containing 0–1.2% NaCl
exhibited in all cases the same generation time and simultaneous onset of the stationary phase while the total viable number
of cells was the same for three continuous generations. The nodulation, plant yield and elemental composition ofMedicago sativa plants grown on agar slopes, inoculated with cultures from the third generation grown on broth containing 0–1.2% NaCl responded
identically to all inocula. The salinity tolerance of the strain in fixing nitrogen was furthermore demonstrated withM. sativa plants grown on either nitrogen-free agar slopes containing 0.2–1.2% NaCl or soil-agar slopes with saline soil in which 0.15
and 0.3% additional NaCl was used. 相似文献
7.
Ainhoa Magrach José Guitián Asier R. Larrinaga Javier Guitián 《Ecological Research》2011,26(4):851-861
The process of fragmentation can greatly influence plant–animal interactions. To assess the degree to which it affects the
balance between two interactions of opposite sign, namely seed dispersal and post-dispersal seed predation, we selected 16
patches of chestnut forest in O Courel and El Bierzo, northwestern Spain. We assessed the effect of fragmentation over two
different seed dispersal–predation systems using Helleborus foetidus and Ilex aquifolium as model species. In the first case, field experiments consisted of seed-offering trays with selective exclusion of rodents and ants in a two-way
orthogonal design. In the second experiment, we placed experimental branches and trays on the floor to assess seed dispersal
and predation. The interactions between several fragment traits and the relative contribution of rodents, ants and birds to
seed removal were analyzed by means of generalized linear mixed models. Results show that for H. foetidus, differences in seed dispersal–predation were accounted for by patch shape, which affected mainly the dispersal phase. Major
seed dispersal took place in patches with a smaller edge to core ratio and high plant cover (abandoned patches), whilst the
latter also showed maximum seed predation. For I. aquifolium, fragmentation effects were significant only for seed predation, which was increased in abandoned patches. This shows that
the effects of habitat fragmentation can emerge at different phases depending on specific traits of the interacting animals.
It also highlights the importance of traditional land-use practices in species interactions. 相似文献
8.
Yves Gingras 《Journal of the history of biology》2010,43(1):159-181
The object of this paper is two-fold: first, to show that contrary to what seem to have become a widely accepted view among
historians of biology, the famous 1953 first Nature paper of Watson and Crick on the structure of DNA was widely cited – as compared to the average paper of the time – on a
continuous basis from the very year of its publication and over the period 1953–1970 and that the citations came from a wide
array of scientific journals. A systematic analysis of the bibliometric data thus shows that Watson’s and Crick’s paper did
in fact have immediate and long term impact if we define “impact” in terms of comparative citations with other papers of the
time. In this precise sense it did not fall into “relative oblivion” in the scientific community. The second aim of this paper
is to show, using the case of the reception of the Watson–Crick and Jacob–Monod papers as concrete examples, how large scale
bibliometric data can be used in a sophisticated manner to provide information about the dynamic of the scientific field as
a whole instead of limiting the analysis to a few major actors and generalizing the result to the whole community without
further ado. 相似文献
9.
Pseudomonas oleovorans and recombinant strains containing the alkane oxidation genes can produce alkane oxidation products in two‐liquid phase bioreactor systems. In these bioprocesses the cells, which grow in the aqueous phase, oxidize apolar, non‐water soluble substrates. The apolar products typically accumulate in the emulsified apolar phase. We have studied both the bioconversion systems and several downstream processing systems to separate and purify alkanols from these two‐liquid phase media. Based on the information generated in these studies, we have now designed bioconversion and downstream processing systems for the production of 1‐alkanols from n‐alkanes on a 10 kiloton/yr scale, taking the conversion of n‐octane to 1‐octanol as a model system. Here, we describe overall designs of fed‐batch and continuous‐fermentation processes for the oxidation of octane to 1‐octanol by Pseudomonas oleovorans, and we discuss the economics of these processes. In both systems the two‐liquid phase system consists of an apolar phase with hexadecene as the apolar carrier solvent into which n‐octane is dissolved, while the cells are present in the aqueous phase. In one system, multiple‐batch fermentations are followed by continuous processing of the product from the separated apolar phase. The second system is based on alkane oxidation by continuously growing cultures, again followed by continuous processing of the product. Fewer fermentors were required and a higher space‐time‐yield was possible for production of 1‐octanol in a continuous process. The overall performance of each of these two systems has been modeled with Aspen software. Investment and operating costs were estimated with input from equipment manufacturers and bulk‐material suppliers. Based on this study, the production cost of 1‐octanol is about 7 US$kg−1 when produced in the fed‐batch process, and 8 US$kg−1 when produced continuously. The comparison of upstream and downstream capital costs and production costs showed significantly higher upstream costs for the fed‐batch process and slightly higher upstream costs for continuous fermentation. The largest cost contribution was due to variable production costs, mainly resulting from media costs. The organisms used in these systems are P. putida alk+ recombinants which oxidize alkanes, but cannot oxidize the resulting alkanols further. Hence, such cells need a second carbon source, which in these systems is glucose. Although the continuous process is about 10% more expensive than the fed‐batch process, improvements to reduce overall cost can be achieved more easily for continuous than for fed‐batch fermentation by decreasing the dilution rate while maintaining near constant productivity. Improvements relevant to both processes can be achieved by increasing the biocatalyst performance, which results in improved overall efficiency, decreased capital investment, and hence, decreased production cost. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 84: 459–477, 1999. 相似文献
10.
The effect of long-term nitrate treatment on SRB activity,corrosion rate and bacterial community composition in offshore water injection systems 总被引:1,自引:0,他引:1
Bødtker G Thorstenson T Lillebø BL Thorbjørnsen BE Ulvøen RH Sunde E Torsvik T 《Journal of industrial microbiology & biotechnology》2008,35(12):1625-1636
Biogenic production of hydrogen sulphide (H2S) is a problem for the oil industry as it leads to corrosion and reservoir souring. Continuous injection of a low nitrate
concentration (0.25–0.33 mM) replaced glutaraldehyde as corrosion and souring control at the Veslefrikk and Gullfaks oil field
(North Sea) in 1999. The response to nitrate treatment was a rapid reduction in number and activity of sulphate-reducing bacteria
(SRB) in the water injection system biofilm at both fields. The present long-term study shows that SRB activity has remained
low at ≤0.3 and ≤0.9 μg H2S/cm2/day at Veslefrikk and Gullfaks respectively, during the 7–8 years with continuous nitrate injection. At Veslefrikk, 16S rRNA
gene based community analysis by PCR–DGGE showed that bacteria affiliated to nitrate-reducing sulphide-oxidizing Sulfurimonas (NR–SOB) formed major populations at the injection well head throughout the treatment period. Downstream of deaerator the
presence of Sulfurimonas like bacteria was less pronounced, and were no longer observed 40 months into the treatment period. The biofilm community
during nitrate treatment was highly diverse and relative stable for long periods of time. At the Gullfaks field, a reduction
in corrosion of up to 40% was observed after switch to nitrate treatment. The present study show that nitrate injection may
provide a stable long-term inhibition of SRB in sea water injection systems, and that corrosion may be significantly reduced
when compared to traditional biocide treatment. 相似文献
11.
Phosphatidylinositol polyphosphates (PI-PPs) have been shown to mediate a large variety of physiological processes by attracting proteins to specific cellular sites. Such site-specific signaling requires local accumulation of PI-PPs, and in light of the rich headgroup functionality, it is conceivable that hydrogen bond formation between adjacent headgroups is a contributing factor to the formation of PI-PP-enriched domains. To explore the significance of hydrogen bond formation for the mutual interaction of PI-PPs, this study aims to characterize the pH-dependent phase behavior of phosphatidylcholine/phosphatidylinositol bisphosphate and trisphosphate mixed vesicles by differential scanning calorimetry, infrared transmission spectroscopy, and fluorescence resonance energy transfer measurements. For pH values >7-7.5, the experiments yielded results consistent with dipalmitoylphosphatidylcholine/dipalmitoylphosphatidylinositol polyphosphate gel phase demixing, whereas for moderately acidic conditions, an enhanced mixing was observed. Similarly, this pH-dependent formation of PI-PP-enriched domains was also found for the physiologically important fluid phase. The stability of PI-PP-enriched domains and to some extent the pH dependence of the domain formation was governed by the number as well as the position of the phosphomonoester groups at the inositol ring. 相似文献
12.
Many food and encapsulation products are dispersed systems with a highly viscous concentrated carbohydrate solution or melt
as the continuous phase and for which interfacial properties are important at high temperatures. A drop volume interfacial
tensiometer was utilized to provide objective characterization of surfactant behavior in such systems at temperatures typical
of food production processes. Interfacial tension was measured over a range of flow rates within a maltodextrin–sucrose–water
melt at 105 °C using limonene as the oil phase and a sucrose ester surfactant. The results showed that the kinetics of surfactant
adsorption were faster when the surfactant was dissolved in the oil phase. However, the low critical micelle concentration
in the oil phase resulted in a lower than expected diffusion coefficient. 相似文献
13.
Soil nutrients in arid systems are supplied to plants in brief pulses following precipitation inputs. While these resource
dynamics have been well documented, little is known about how this temporal heterogeneity influences competitive interactions.
We examined the impacts of the temporal pattern of N supply on competitive intensity and ability in an N-limited desert shrub
community. At our field site, the three codominant shrubs, Atriplex confertifolia, A. parryi, and Sarcobatus vermiculatus, differ in seasonal growth patterns, with A. confertifolia and S. vermiculatus achieving higher growth rates earlier in the growing season than A. parryi. We predicted that these timing differences in maximum growth rate may interact with temporal variation in N supply to alter
competitive abilities over time. Seedlings of the two Atriplex species were planted either individually in field plots or as target plants surrounded by neighbor seedlings. After one year
of establishment, the same amount of 15N was applied to plots either as early spring pulses, mid spring pulses or continuously through the second growing season.
Competitive effects were observed under continuous and pulsed N supply. Averaged across all target–neighbor treatments, competitive
intensity was ∼1.8-fold greater when N was pulsed compared to when N was supplied continuously, but overall, the outcome of
competitive interactions was not influenced by N pulse timing. While the timing of resource supply did not differentially
influence the competitive abilities of coexisting species in this system, the temporal pattern of resource supply did alter
the intensity of competitive interactions among species. While additional studies in other systems are needed to evaluate
the generality of these results, this study suggests that competitive intensity may not necessarily be a direct function of
productivity or resource availability as traditionally assumed. Instead, the intensity of competitive interactions in resource-poor
systems may depend upon the temporal pattern of resource supply. 相似文献
14.
Lipid and docosahexaenoic acid (DHA) accumulation into Schizochytrium G13/2S was studied under batch and continuous culture. Different glucose and glutamate concentrations were supplemented in
a defined medium. During batch cultivation, lipid accumulation, 35% total fatty acids (TFA) occurred at the arithmetic growth
phase but ceased when cell growth stopped. When continuous culture was performed under different glutamate concentrations,
nitrogen-growth-limiting conditions induced the accumulation of 30–28% TFA in Schizochytrium. As the dilution rate decreased from 0.08 to 0.02 h−1, both cell dry weight and TFA content of the cell increased. Under a constant dilution rate of 0.04 h−1, carbon-limiting conditions decreased the TFA to 22%. Fatty acid profile was not affected by the different nutrient concentrations
provided during continuous culture. Consequently, lipid accumulation can be induced through the carbon and nitrogen source
concentration in the medium to maximise the TFA and subsequently DHA productivity by this microorganism. 相似文献
15.
M. H. Salamanca J. C. Merchuk B. A. Andrews J. A. Asenjo 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1998,711(1-2)
The effect of the tie-line location (phase volume ratio) on the kinetics of phase separation in batch PEG/salt aqueous two-phase systems (ATPS) has been investigated. PEG/sulphate systems with a stability ratio (sr) of 0.34 and 0.37 and relative tie-line lengths in the range 0.1 to 0.6 for a continuous top phase and in the range 0.03 to 0.15 for a continuous bottom phase were used in the batch studies. A continuous settler was designed with three different inlet geometries. Phase separation is much faster when the bottom phase is continuous and in this case the location on the tie-line and the presence or absence of Bacillus subtilis extract makes little difference. When the top phase is continuous the relative sizes of the phases (phase ratio, R, relative distance on tie-line, rd) has an important effect, the larger the top phase (larger R and rd) the slower the phase separation. The presence of Bacillus extract also makes the operation slower which is more marked at the largest values of R (and rd). At the largest volume ratios (R or rd) three different settling regions have been recognised, a region of coalescence, a region of drops moving to the interphase and a region where drops queue at the interphase to coalesce into the large phase. A modified correlation that takes into account the location on the tie-line and thus volume ratio (R) and relative distance (rd) has been proposed and successfully tested. The behavior of batch and continuous systems in the presence and absence of Bacillus subtilis extract in systems with continuous bottom phase was also studied. The settling velocity was lower in the continuous than in the batch systems, and in both cases the initial rate was lower in the presence of Bacillus extract. 相似文献
16.
Visual evoked potentials (EP) were recorded when the test subjects accomplished the tasks of a comparison of a current stimulus
with the previous one, the stimuli being presented in a continuous sequence. In the first task, rare repetition of two stimuli
(Russian letters) in the continuously changing flow of stimuli was relevant, and the test subject had to press the button
when it happened; in the second task, the relevant stimulus was a rare change in the flow of stimuli. The influence of the
stimulus repetition/change factor on EP was analyzed. The processes related to the comparison of the current and previous
stimuli were most manifest in four time intervals: 120–140, 180–210, 260–280, and 350–370 ms. The occipito-temporal component
of EP revealed in the interval of 180–210 ms, which we denoted as the negative component of visual mismatch (NCVM), proved
a special component, differing in its functional and temporal characteristics from theN
2b component. WhereasN
2b is modulated by the factor of stimulus probability, the NCVM by that of stimulus repetition/change. 相似文献
17.
B. A. Hills 《Bulletin of mathematical biology》1968,30(1):47-59
In this paper an expression is derived which describes the transient overall uptake of an inert solute by a section of tissue
excised with parallel faces and placed upon an impermeable base. The approach diverges from the conventional analyses for
perfused tissue (Morales and Smith,Bull. Math. Biophysics,6, 125–141, 1944;7, 47–99, 1945) because the extravascular zone is regarded as a heterogeneous diffusion medium. Account for this is taken by
regarding tissue as effectively composed of two phases—a continuous (extracellular) phase similar to water, and a dispersed
phase comprising cells of irregular profile. In both phases the relevant mode of uptake is taken as bulk diffusion rather
than surface permeation, thus emphasizing the influence of the internal geometry of the tissue upon its overall exchange response. 相似文献
18.
The changes in the marriage structure with respect to the age at marriage, ethnicity, and spouses’ birthplaces during the
period of time corresponding to two generations have been analyzed in the rural population of Shors of Tashtagolskii raion
of Kemerovo oblast. In general, the Shor population had a high assortative marriage rate with respect to these parameters
in the period studied, although there was a temporary tendency to wards its decrease. The ages of marriage for both the male
and the female Shor populations in the years 2000–2005 were significantly older than in 1940–1945 and 1970–1975. The age-assortative
marriage rate was r = 0.60 in 1940-1945, r = 0.73 in 1970–1975, and r = 0.66 in 2000–2005. The birthplace-assortative marriage rate decreased from 79.63% in 1970–1975 to 70.64% in 2000–2005.
The ethnic assortative marriage rate of Shors steadily decreased during the time interval studied; it was 96.92, 89.95, and
80.98% in 1940–1945, 1970–1975, and 2000–2005, respectively, for the total rural population of Tashtagolskii raion. 相似文献
19.
Group-living animals may need to spend less time being vigilant, consequently, having more time for other important activities
such as foraging (i.e., group size effect). Przewalski’s gazelle (Procapra przewalskii) is a group-living social animal, and a study was conducted in Qinghai Province of China during June–August 2006 by using
a continuous focal sampling method to investigate the influences of group size, sex, within-group spatial position, and nearest-neighbor
distance on individual vigilance level (defined as scanning frequency per minute). Male gazelles were more vigilant than females.
The gazelle’s vigilance level decreased with group size (group size effect), but only for females. The individuals at the
central positions within a group were less vigilant than those at the peripheral positions, but the nearest-neighbor distance
did not have any significant influence on the individual vigilance level. Our results support the hypotheses of group size
effect and edge effects, but the sexual difference in vigilance level and in the response to group size effect on vigilance
suggests that there may be sexual difference in the function and targets of vigilance behavior of Przewalski’s gazelles, which
warrants more investigation, with incorporation of within-group spatial position, to better understand the mechanism underlying
the group size effect and edge effect. 相似文献
20.
Takehiko Yamanaka Koichi Tanaka Akira Otuka Ottar N. Bjørnstad 《Ecological Research》2007,22(2):185-196
We observed a weed (Ambrosia artemissifolia)–beetle herbivore (Ophraella communa) system for three years in a spatially continuous field (≈200 ha). We analyzed our field data in the light of two contrasting
theories: the resource-concentration hypothesis and reaction–diffusion theory. For the resource-concentration hypothesis, we calculated the correlation coefficients between weed and beetle abundances
for every season in each year. Although we found weak support for resource concentration in some seasons, we could not find
any clear relationships in other seasons. We discuss a dispersal-based mechanism to explain the differences observed among
seasons in lieu of the resource-concentration hypothesis. For the reaction–diffusion theory, we estimated the nonparametric
spatial covariance functions for the spatial autocorrelation of weeds and beetles. Although we could not find any strong spatial
structure for the individual species, we found evidence of spatial interactions between weeds and beetles using time lagged
cross-correlation functions. Weed abundance enhanced local beetle abundance. Through time, there was evidence of beetle spillover
to adjacent locations at roughly the one beetle-generation time scale. Sites with large number of beetles did not seem to
reduce subsequent weed abundance. 相似文献