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Bulk Liquid (bulk + liquid)
Selected AbstractsDirect Observation of Anion-Mediated Translocation of Fluorescent Oligoarginine Carriers into and across Bulk Liquid and Anionic Bilayer MembranesCHEMBIOCHEM, Issue 1 2005Naomi Sakai Dr. Abstract The recent hypothesis that counteranion-mediated dynamic inversion of charge and solubility might contribute to diverse functions of oligoarginines in biomembranes was tested with two fluorescently labelled oligomers, FL-R8, one of the most active cell-penetrating peptides, and its longer version, FL-R16. We report evidence for counteranion-mediated phase transfer from water into bulk chloroform and anionic lipid-bilayer membranes as well as reverse-phase transfer from bulk chloroform and across intact lipid-bilayer membranes into water. The differences found between FL-R8 and FL-R16 with regard to location in the bilayer and reverse-phase transfer from bulk and lipid-bilayer membranes into water implied that the reported results may be relevant for biological function. [source] Temperature measurements near a heating surface at high heat fluxes in subcooled pool boilingHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2010Ayako Ono Abstract In previous papers (Int J Heat Mass Transfer, 2008;50:3481,3489, 2009;52: 814,821), the authors conducted measurements of liquid,vapor structures in the vicinity of a heating surface for subcooled pool boiling on an upward-facing copper surface by using a conducting probe method. We reported that the macrolayer dryout model is the most appropriate model of the CHF and that the reason why the CHF increases with increasing subcooling is most likely that a thick macrolayer is able to form beneath large vapor masses and the lowest heat flux of the vapor mass region shifts towards the higher heat flux. To develop a mechanistic model of the CHF for subcooled boiling, therefore, it is necessary to elucidate the effects of local subcooling on boiling behaviors in the vicinity of a heating surface. This paper measured local temperatures close to a heating surface using a micro-thermocouple at high heat fluxes for water boiling on an upward-facing surface in the 0 to 40 K range of subcooling. A value for the effective subcooling, defined as the local subcooling during the period while vapor masses are being formed was estimated from the detected bottom peaks of the temperature fluctuations. It was established that the effective subcooling adjacent to the surface remains at considerably lower values than the bulk liquid subcooling. This suggests that, from nucleation to coalescence, the subcooling of a bulk liquid has a smaller effect on the behavior of primary bubbles than the extent of the subcooling would appear to suggest. An empirical correlation of the effective subcooling is proposed to provide a step towards quantitative modeling of the CHF for subcooled boiling. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20277 [source] Pool boiling heat transfer in binary mixtures of ammonia/water: Effect of heat of dilution and dissolution on heat transfer coefficientHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2002Toshiaki Inoue Abstract Nucleate boiling heat transfer coefficients were measured on a horizontal heated wire during the pool boiling of non-azeotropic mixtures of ammonia/water. The experiment was carried out at pressures of 0.4 and 0.7 MPa, at heat fluxes below 2.0 × 106 W/m2, and over a range of mass fraction. The heat transfer coefficients in the mixtures were smaller than those in single-component substances. No existing correlation is found to predict boiling heat transfer coefficients over the range of mass fraction of interest. In the mixtures of the ammonia/water, the heats of dilution and dissolution were generated near a liquid surface while vapor with a rich concentration of ammonia was condensed and then was diffused into the bulk liquid; while in most other mixtures, little heat was generated during any dilution and dissolution. In relation to the heat generated, the effect of the heats of dilution and dissolution on pressure and temperature in a system (pressure vessel) is shown herein. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(4): 272,283, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10034 [source] Solid,liquid mass transfer characteristics of an unbaffled agitated vessel with an unsteadily forward,reverse rotating impellerJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2008Shuichi Tezura Abstract To develop an enhanced form of solid-liquid apparatus, an unbaffled agitated vessel has been constructed, fitted with an agitation system using an impeller whose rotation alternates unsteadily in direction, i.e. a forward-reverse rotating impeller. In this vessel, solid-liquid mass transfer was studied using a disc turbine impeller with six flat blades. The effect of impeller rotation rate as an operating variable on the mass transfer coefficient was evaluated experimentally using various geometrical conditions of the apparatus, such as impeller diameter and height, in relation to the impeller power consumption. Mixing of gas above the free surface into the bulk liquid, i.e. surface aeration, which accompanied the solid-liquid agitation, was also investigated. Comparison of the mass transfer characteristics between this type of vessel and a baffled vessel with a unidirectional rotating impeller underscored the sufficient solid-liquid contact for prevention of gas mixing in the forward-reverse rotation mode of the impeller. Copyright © 2008 Society of Chemical Industry [source] The effect of headspace pressure on the performance of a fluidised-bed bioreactorJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 10 2002J Fung Abstract This study compares the biological performance of three fluidised-bed biological reactors under conditions of different headspace pressures. The application of pressure can have a profound effect on the initial rate of bed growth. However, once the fluidised-bed reaches full expansion, the biological performance at higher pressures is greater than those at lower pressures. There appears to be an almost linear relationship between the application of pressure and the performance of the fluidised-bed biological reactors in removing soluble BOD5. This can be attributed to the increase in the oxygen concentration in the bulk liquid and a greater oxygen penetration depth within the biofilm. © 2002 Society of Chemical Industry [source] Increased biofilm activity in BGAC reactorsAICHE JOURNAL, Issue 3 2005Moshe Herzberg Abstract In bioreactors systems granulated activated carbon (GAC) was proven to be an advantageous biofilm carrier over inert media with similar physical properties (nonadsorbing carbon) under conditions of pollutant partial penetration in the biofilm. Results from laboratory experiments using atrazine degrading bacteria (Pseudomonas ADP) and modeling assuming GAC adsorption/desorption mechanism, showed higher atrazine degradation rate resulting in better effluent quality in the biofilm granulated activated carbon (BGAC) reactor. Increased biofilm activity due to the double flux of substrate from the bulk liquid and from the GAC can explain the better performance of the BGAC reactor. © 2005 American Institute of Chemical Engineers AIChE J, 51: 1042,1047, 2005 [source] Modeling of protein breakthrough performance in cryogel columns by taking into account the overall axial dispersionJOURNAL OF SEPARATION SCIENCE, JSS, Issue 15-16 2009Junxian Yun Abstract A model considering the overall axial dispersion for describing protein adsorption and breakthrough in monolithic cryogel beds has been developed. The microstructure of cryogels was characterized by tortuous capillaries with a normal diameter distribution but a constant pore wall thickness. The axial dispersion within cryogel columns was described by using the overall axial dispersion coefficient, which can be easily obtained by matching the experimental breakthrough curves without adsorption or measuring residence time distributions (RTDs). Experimental breakthrough curves of lysozyme within a metal-chelated affinity cryogel by Persson et al. (Biotechnol. Bioeng. 2004, 88, 224,236) and a cation-exchange cryogel by Yao et al. (J. Chromatogr. A 2007, 1157, 246,251) were employed as examples to test the model. The results showed that by using the axial dispersion coefficient and assuming uniform radial concentration profile at a given cross-section of the cryogel along the bed height, the model can describe the detailed behaviors of the in-bed overall axial dispersion, the in-pore mass transfer, as well as the protein adsorption and breakthrough. For a known overall axial dispersion coefficient, the lumped parameter of the mass transfer coefficient between the bulk liquid and the capillary wall can be determined by fitting the protein breakthrough curve at a known chromatographic condition. Once this parameter is determined, the model can be used to predict the protein breakthrough profiles under different conditions based on the basic physical parameters of the cryogel bed and the properties of the fluid and protein. The effective capillary diameters employed in the model are close to the actual pore sizes observed from the images by SEM. The model predictions of lysozyme breakthrough profiles at various flow rates are also in good agreement with the experimental data in both the metal-chelated affinity and cation-exchange cryogel columns. [source] Chlorophyll a Self-assembly in Polar Solvent,Water Mixtures ,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2000Radka Vladkova ABSTRACT The conversion of chlorophyll a (Chl a) monomers into large aggregates in six polar solvents upon addition of water has been studied by means of absorption, fluorescence spectroscopy and fluorescence lifetime measurements for the purpose of elucidating the various environmental factors promoting Chl a self-assembly and determining the type of its organization. Two empirical solvent parameter scales were used for quantitative characterization of the different solvation properties of the solvents and their mixtures with water. The mole fractions of water f1/2 giving rise to the midpoint values of the relative fluorescence quantum yield were determined for each solvent, and then various solvent,water mixture parameters for the f1/2 values were compared. On the basis of their comparison, it is concluded that the hydrogen-bonding ability and the dipole,dipole interactions (function of the dielectric constant) of the solvent,water mixtures are those that promote Chl a self-assembly. The influence of the different nature of the nonaqueous solvents on the Chl aggregation is manifested by both the different water contents required to induce Chl monomer , aggregate transition and the formation of two types of aggregates at the completion of the transition: species absorbing at 740,760 nm (in methanol, ethanol, acetonitrile, acetone) and at 667,670 nm (in pyridine and tetrahydrofuran). It is concluded that the type of Chl organization depends on the coordination ability and the polarizability (function of the index of refraction) of the organic solvent. The ordering of the solvents with respect to the f1/2 values,methanol < ethanol < acetonitrile < acetone < pyridine < tetrahydrofuran,yielded a typical lyotropic (Hofmeister) series. On the basis of this solvent ordering and the disparate effects of the two groups of solvents on the Chl a aggregate organization, it is pointed out that the mechanism of Chl a self-assembly in aqueous media can be considered a manifestation of the Hofmeister effect, as displayed in the lipid-phase behavior (Koynova et al., Eur. J. Biophys. 25, 261,274, 1997). It relates to the solvent ability to modify the bulk structure and to distribute unevenly between the Chl,water interface and bulk liquid. [source] Effect of oxygen gradients on the activity and microbial community structure of a nitrifying, membrane-aerated biofilmBIOTECHNOLOGY & BIOENGINEERING, Issue 6 2008Leon S. Downing Abstract Shortcut nitrogen removal, that is, removal via formation and reduction of nitrite rather than nitrate, has been observed in membrane-aerated biofilms (MABs), but the extent, the controlling factors, and the kinetics of nitrite formation in MABs are poorly understood. We used a special MAB reactor to systematically study the effects of the dissolved oxygen (DO) concentration at the membrane surface, which is the biofilm base, on nitrification rates, extent of shortcut nitrification, and microbial community structure. The focus was on anoxic bulk liquids, which is typical in MAB used for total nitrogen (TN) removal, although aerobic bulk liquids were also studied. Nitrifying MABs were grown on a hollow-fiber membrane exposed to 3 mg,N/L ammonium. The MAB intra-membrane air pressure was varied to achieve different DO concentrations at the biofilm base, and the bulk liquid was anoxic or with 2 g,m,3 DO. With 2.2 and 3.5 g,m,3 DO at the biofilm base, and with an anoxic bulk-liquid, the ammonium fluxes were 0.75 and 1.0 g,N,m,2,day,1, respectively, and nitrite was the main oxidized nitrogen product. However, with membrane DO of 5.5 g,m,3, and either zero or 2 g,m,3 DO in the bulk, the ammonium flux was around 1.3 g,N,m,2,day,1, and nitrate flux increased significantly. For all experiments, the cell density of ammonium oxidizing bacteria (AOB) was relatively uniform throughout the biofilm, but the density of nitrite oxidizing bacteria (NOB) decreased with decreasing biofilm DO. Among NOB, Nitrobacter spp. were dominant in biofilm regions with 2 g,m,3 DO or greater, while Nitrospira spp. were dominant in regions with less than 2 g,m,3 DO. A biofilm model, including AOB, Nitrobacter spp., and Nitrospira spp., was developed and calibrated with the experimental results. The model predicted the greatest extent of nitrite formation (95%) and the lowest ammonium oxidation flux (0.91 g,N,m,2,day,1) when the membrane DO was 2 g,m,3 and the bulk liquid was anoxic. Conversely, the model predicted the lowest extent of nitrite formation (40%) and the highest ammonium oxidation flux (1.5 g,N,m,2,day,1) when the membrane-DO and bulk-DO were 8 g,m,3 and 2 g,m,3, respectively. The estimated kinetic parameters for Nitrospira spp., revealed a high affinity for nitrite and oxygen. This explains the dominance of Nitrospira spp. over Nitrobacter spp. in regions with low nitrite and oxygen concentrations. Our results suggest that shortcut nitrification can effectively be controlled by manipulating the DO at the membrane surface. A tradeoff is made between increased nitrite accumulation at lower DO, and higher nitrification rates at higher DO. Biotechnol. Bioeng. © 2008 Wiley Periodicals, Inc. [source] CHARMM fluctuating charge force field for proteins: I parameterization and application to bulk organic liquid simulationsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2004Sandeep Patel Abstract A first-generation fluctuating charge (FQ) force field to be ultimately applied for protein simulations is presented. The electrostatic model parameters, the atomic hardnesses, and electronegativities, are parameterized by fitting to DFT-based charge responses of small molecules perturbed by a dipolar probe mimicking a water dipole. The nonbonded parameters for atoms based on the CHARMM atom-typing scheme are determined via simultaneously optimizing vacuum water-solute geometries and energies (for a set of small organic molecules) and condensed phase properties (densities and vaporization enthalpies) for pure bulk liquids. Vacuum solute-water geometries, specifically hydrogen bond distances, are fit to 0.19 Å r.m.s. error, while dimerization energies are fit to 0.98 kcal/mol r.m.s. error. Properties of the liquids studied include bulk liquid structure and polarization. The FQ model does indeed show a condensed phase effect in the shifting of molecular dipole moments to higher values relative to the gas phase. The FQ liquids also appear to be more strongly associated, in the case of hydrogen bonding liquids, due to the enhanced dipolar interactions as evidenced by shifts toward lower energies in pair energy distributions. We present results from a short simulation of NMA in bulk TIP4P-FQ water as a step towards simulating solvated peptide/protein systems. As expected, there is a nontrivial dipole moment enhancement of the NMA (although the quantitative accuracy is difficult to assess). Furthermore, the distribution of dipole moments of water molecules in the vicinity of the solutes is shifted towards larger values by 0.1,0.2 Debye in keeping with previously reported work. © 2003 Wiley Periodicals, Inc. J Comput Chem 25: 1,15, 2004 [source] Effect of oxygen gradients on the activity and microbial community structure of a nitrifying, membrane-aerated biofilmBIOTECHNOLOGY & BIOENGINEERING, Issue 6 2008Leon S. Downing Abstract Shortcut nitrogen removal, that is, removal via formation and reduction of nitrite rather than nitrate, has been observed in membrane-aerated biofilms (MABs), but the extent, the controlling factors, and the kinetics of nitrite formation in MABs are poorly understood. We used a special MAB reactor to systematically study the effects of the dissolved oxygen (DO) concentration at the membrane surface, which is the biofilm base, on nitrification rates, extent of shortcut nitrification, and microbial community structure. The focus was on anoxic bulk liquids, which is typical in MAB used for total nitrogen (TN) removal, although aerobic bulk liquids were also studied. Nitrifying MABs were grown on a hollow-fiber membrane exposed to 3 mg,N/L ammonium. The MAB intra-membrane air pressure was varied to achieve different DO concentrations at the biofilm base, and the bulk liquid was anoxic or with 2 g,m,3 DO. With 2.2 and 3.5 g,m,3 DO at the biofilm base, and with an anoxic bulk-liquid, the ammonium fluxes were 0.75 and 1.0 g,N,m,2,day,1, respectively, and nitrite was the main oxidized nitrogen product. However, with membrane DO of 5.5 g,m,3, and either zero or 2 g,m,3 DO in the bulk, the ammonium flux was around 1.3 g,N,m,2,day,1, and nitrate flux increased significantly. For all experiments, the cell density of ammonium oxidizing bacteria (AOB) was relatively uniform throughout the biofilm, but the density of nitrite oxidizing bacteria (NOB) decreased with decreasing biofilm DO. Among NOB, Nitrobacter spp. were dominant in biofilm regions with 2 g,m,3 DO or greater, while Nitrospira spp. were dominant in regions with less than 2 g,m,3 DO. A biofilm model, including AOB, Nitrobacter spp., and Nitrospira spp., was developed and calibrated with the experimental results. The model predicted the greatest extent of nitrite formation (95%) and the lowest ammonium oxidation flux (0.91 g,N,m,2,day,1) when the membrane DO was 2 g,m,3 and the bulk liquid was anoxic. Conversely, the model predicted the lowest extent of nitrite formation (40%) and the highest ammonium oxidation flux (1.5 g,N,m,2,day,1) when the membrane-DO and bulk-DO were 8 g,m,3 and 2 g,m,3, respectively. The estimated kinetic parameters for Nitrospira spp., revealed a high affinity for nitrite and oxygen. This explains the dominance of Nitrospira spp. over Nitrobacter spp. in regions with low nitrite and oxygen concentrations. Our results suggest that shortcut nitrification can effectively be controlled by manipulating the DO at the membrane surface. A tradeoff is made between increased nitrite accumulation at lower DO, and higher nitrification rates at higher DO. Biotechnol. Bioeng. © 2008 Wiley Periodicals, Inc. [source] Effects of Physical Property Differences on BlendingCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2005P. N. Jones Abstract Within this study, the effects of viscosity differences between added and bulk liquids on mixing times were investigated. This was carried out in stirred tanks of diameter T,=,0.31, 0.61, 1.83,m to study the effect of scale. Different impeller types (hydrofoils, disc turbines, and pitched blade turbines) and sizes (D,=,T/2 and T/3) were employed. Operating conditions for which mixing time correlations for similar property liquids could be used were identified at scales relevant to industrial applications. Recommendations are made for improving blending under operating conditions where these correlations are not applicable as the mixing times are too long. [source] | |||||||||||||