Biomedical subjects

D J Lee

Publications and source records attributed to D J Lee.

At least 73 records · Page 4Linked to original sources

PubMed2002

Batch gravitational sedimentation of slurries.

We investigated the batch settling behavior of the kaolin slurry and the UK ball clay slurry at various initial solids fractions (phi(0)s) using a computerized axial tomography scanner (CATSCAN). The spatio-temporal evolutions of solids fractions in the consolidating sediments were continuously monitored. Since the interface between the sediment and the supernatant of the investigated slurries was blurred, an averaging procedure was employed to estimate their null-stress solids fractions (phi(g)s). Besides the rather slow settling for the high-phi(0) slurries, the basic settling characteristics resemble each other regardless of whether phi(0)>phi(g) or vice versa. The above-mentioned experimental data reveal that the investigated slurries are neither purely elastic nor purely plastic in rheological behavior. On contrary to most model works a blurred supernatant-sediment interface makes difficulty in the gel point determination. During initial settling the high-phi(0) slurries clearly exhibit a finite yield stress to resist deformation. That is, the slurries are plastic fluids. However, the network structure in the slurries deteriorates gradually in the subsequent settling stage while the final, equilibrated sediment reveals a continuous distribution in solids fraction. Restated, the final sediment possesses as a purely elastic characteristic. The model parameters of theory by Buscall and White were regressed by the dynamic consolidating sediment data, while those by Tiller and Leu were obtained using the final equilibrated sediment data. Calculations from both models reveal that ball clay slurry is more compressible than is the kaolin slurry. The high-phi(S0) slurry would yield the less compressible sediment.

Journal Article↗

PubMed2002

Network strength and dewaterability of flocculated activated sludge.

Works in literature proposed the use of the rheological properties of wastewater sludges as an index for conditioner assessment and control. We demonstrated in this work, on the contrary, that one could not justify the consistency of the commonly used rheological characteristics of the sewage sludge samples taken from the same site but at different dates. A physically relevant index was proposed instead for describing the total network strength, which was hypothesized to correlate the dewatering efficiency of flocculated sludge. Based on this index, the network of a sludge was demonstrated to be largely destroyed after shearing, while the relaxation in an unbound environment or mild pouring over action could partially reinstall the structure. Moreover, a uniform shear rate field could produce network of greater strength when compared with that conditioned in a stirred tank.

Flocculation↗

PubMed2002

"Weak" ultrasonic pre-treatment on anaerobic digestion of flocculated activated biosolids.

This study examined how "weak" ultrasonic pre-treatment affects anaerobic digestion of waste biosolids, treated with a cationic polyelectrolyte flocculant. In relation to pre-treatment, the term "weak" used refers to the fact that the total ultrasonic energy input to biosolids is insufficient to fully disrupt its floc structure or the cell walls, as described in the literature. Methane production potential, floc characteristics (size, morphology and zeta-potential) and process parameters (chemical oxygen demands and oxidative-reductive potentials) were monitored, as the digestion was tested. The presence of polyelectrolyte flocculants enhanced methane production within 6 days of digestion (phase I), but inhibited the digestion thereafter (phase II). Following pre-treatment by sonication (0.33 W/mL, 20 min), the methane productions of both original and flocculated biosolids significantly increased. The underlying mechanisms of weak ultrasonic pre-treatment are discussed.

Bacteria, Anaerobic↗

PubMed2002

Regional and processor variation in the ileal digestible amino acid content of soybean meals measured in growing swine.

To assess differences in soybean meal quality related to region of production, researchers in Illinois, Kansas, North Carolina, The Netherlands, and Ohio collected four soybean meal samples processed locally at least 15 d apart. These samples were assayed for ileal amino acid digestibility by pigs using a common soybean meal and a soy protein concentrate as references, and a low-protein casein diet for determination of endogenous amino acid losses. Digestibility was determined at each university using seven barrows surgically fitted with ileal cannulas in a 7 x 7 Latin square design. The experimental diets contained 17% CP from the test material except for the low-protein casein diet. Animals were fed twice daily, 12 h apart, at a level of 45 g x kg(-0.75) BW for each meal. Following a 5-d adaptation period, ileal digesta were collected for two 12-h periods for 2 d to be used for determination of ileal digestibility. Variation in amino acid digestibility was very small among and within sites and was much smaller than variation in the concentration of amino acids. Among sites, samples from The Netherlands had less total and thus digestible lysine and methionine than the U.S. samples (P < 0.05). The soybean meals tested in this experiment were approximately 4% higher in amino acids than that reported in the NRC (1998). True (standardized) digestibilities, however, were very similar to NRC values except for cysteine and threonine, which were 5 and 3 percentage points lower in this experiment, respectively. In conclusion, soybeans grown in the United States and locally processed into soybean meal were very similar in nutritional composition. Soybean meals produced in The Netherlands were lower in lysine and methionine (P < 0.05) but had a digestibility similar to that produced in the United States.

Amino Acids↗

PubMed2001

Using ATP bioluminescence technique for monitoring microbial activity in sludge.

This study demonstrates, for the first time, that the presence of suspended solids in waste-activated sludge interferes with adenosine triphosphate (ATP) bioluminescence tests. The sludge subject to acid/alkaline treatment represented the test sample. Without consideration of the effect of solid concentrations, one would erroneously estimate the density levels of heterotrophic bacteria in the sludge using ATP data. A light blockage model was proposed to evaluate the luminescence reading without the interference of suspended solids.

Adenosine Triphosphate↗

PubMed2001

Involvement of phosphatidylinositol 3-kinase and mitogen-activated protein kinases in glycine-extended gastrin-induced dissociation and migration of gastric epithelial cells.

The various molecular forms of gastrin can act as promoters of proliferation and differentiation in different regions of the gastrointestinal tract. We report a novel stimulatory effect of glycine-extended gastrin(17) only on cell/cell dissociation and cell migration in a non-tumorigenic mouse gastric epithelial cell line (IMGE-5). In contrast, both amidated and glycine-extended gastrin(17) stimulated proliferation of IMGE-5 cells via distinct receptors. Glycine-extended gastrin(17)-induced dissociation preceded migration and was blocked by selective inhibitors of phosphatidylinositol 3-kinase (PI3-kinase) but did not require mitogen-activated protein (MAP) kinase activation. Furthermore, glycine-extended gastrin(17) induced a PI3-kinase-mediated tyrosine phosphorylation of the adherens junction protein beta-catenin, partial dissociation of the complex between beta-catenin and the transmembrane protein E-cadherin, and delocalization of beta-catenin into the cytoplasm. Long lasting activation of MAP kinases by glycine-extended gastrin(17) was specifically required for the migratory response, in contrast to the involvement of a rapid and transient MAP kinase activation in the proliferative response to both amidated and glycine-extended gastrin(17). Therefore, the time course of MAP kinase activation appears to be a critical determinant of the biological effects mediated by this pathway. Together with the involvement of PI3-kinase in the dissociation of adherens junctions, long term activation of MAP kinases seems responsible for the selectivity of this novel effect of G(17)-Gly on the adhesion and migration of gastric epithelial cells.

Cell Membrane↗

PubMed2001

Protection from immunodeficiency virus challenges in rhesus macaques by multicomponent DNA immunization.

Multicomponent DNA vaccines were used to elicit immune responses, which can impact viral challenge in three separate rhesus macaque models. Eight rhesus macaques were immunized with DNA vaccines for HIV env/rev and SIV gag/pol and were challenged intravenously with 10 animal infective doses (AID(50)) of cell-free SHIV IIIB. Three of eight immunized rhesus macaques were protected, exhibiting no detectable virus. Animals protected from nonpathogenic SHIVIIIB challenge were rested for extended periods of time and were rechallenged first with pathogenic SIV(mac239) and subsequently with pathogenic SHIV89.6P viruses. Following the pathogenic challenges, all three vaccinated animals were negative for viral coculture and antigenemia and were negative by PCR. In contrast, the control animals exhibited antigenemia by 2 weeks postchallenge and exhibited greater than 10 logs of virus/10(6) cells in limiting dilution coculture. The control animals exhibited CD4 cell loss and developed SIV-related wasting with high viral burden and subsequently failed to thrive. Vaccinated animals remained virus-negative and were protected from the viral load, CD4 loss, disease, and death. We observed strong Th1-type cellular immune responses in the protected macaques throughout the study, suggesting their important roles in protection. These studies support the finding that multicomponent DNA vaccines can directly impact viral replication and disease in a highly pathogenic challenge system, thus potentially broadening our strategies against HIV.

AIDS Vaccines↗

PubMed2001

The roles of MHC class II, CD40, and B7 costimulation in CTL induction by plasmid DNA.

DNA-based vaccines generate potent CTL responses. The mechanism of T cell stimulation has been attributed to plasmid-transfected dendritic cells. These cells have also been shown to express plasmid-encoded proteins and to become activated by surface marker up-regulation. However, the increased surface expression of CD40 and B7 on these dendritic cells is insufficient to overcome the need for MHC class II-restricted CD4(+) T cell help in the priming of a CTL response. In this study, MHC class II(-/-) mice were unable to generate a CTL response following DNA immunization. This deficit in CTL stimulation by MHC class II-deficient mice was only modestly restored with CD40-activating Ab, suggesting that there were other elements provided by MHC class II-restricted T cell help for CTL induction. CTL activity was also augmented by coinjection with a vector encoding the costimulatory ligand B7.1, but not B7.2. These data indicate that dendritic cells in plasmid DNA-injected mice require conditioning signals from MHC class II-restricted T cells that are both CD40 dependent and independent and that there are different roles for costimulatory molecules that may be involved in inducing optimal CTL activity.

Adjuvants, Immunologic↗

PubMed2001

Validation of the RTOG recursive partitioning classification for head and neck tumors.

BACKGROUND: We previously demonstrated that a mathematical technique called recursive partitioning analysis (RPA), when applied to the Radiation Therapy Oncology Group Head and Neck Cancer database, created rules that formed subgroups ("classes") having unique outcomes. We sought to learn if the application of RPA-derived rules to a new head and neck database would create classes that were similarly associated with outcome and thereby validate this technique. METHODS: The rules derived from recursive partitioning analysis of the previous database were used to subgroup an independent, new head and neck cancer database (RTOG 85-27), created as part of a phase III trial of the hypoxic-cell radiosensitizer, Etanidazole. The resulting classes were compared with each other and with the classes formed from the previous database. RESULTS: The rules derived by RPA from our previous database correctly grouped the tumors in the new database into unique classes of similar outcome. RPA could successfully use either survival or local-regional control of disease as the measure of outcome. As judged by comparison of the 95% confidence intervals, the outcome of the classes in the new database is essentially indistinguishable from the outcome of the classes in the previous database. CONCLUSION: RPA-derived rules provide a reliable method to assort head and neck tumors into unique classes that are predictive of outcome. These rules can be successfully applied to new databases that were not used in the creation of the rules and thereby validate the methodology.

Antineoplastic Agents↗

PubMed2001

Slow release of drug through deformed coating film: effects of morphology and drug diffusivity in the coating film.

The effects of the morphology and drug diffusivity in the coating film on the slow release characteristics have been analyzed numerically under the constraint that the volume of the coating film and the drug matrix is maintained constant. Two different systems of coated particles with deformed coating films were studied and their release characteristics compared with those of the coated particles having spherical coating films. The average release rate, fractional release, drug concentration profiles, and the initial burst of drug were found to be strongly influenced by the ratio of drug diffusivity in the coating film to that in the drug matrix D(r) (i.e., dimensionless drug diffusivity in the coating film). Increasing D(r) always increased the release rate, the fractional release, and the initial burst of drug, but reduced the initial lag times of drug release. The effect of shape deformation was very significant in the drug concentration profiles and the initial lag times; in contrast, it was not so substantial on the fractional release and the average release rates. The morphology difference in the deformed systems was also found to affect the release characteristics to different extents. Increasing the degree of the shape deformation, represented by the perturbation parameter epsilon, always reduced the effective surface area for the controlled release of drug. Because of the compensation effects between decreasing surface area and the non-uniform mass flux distribution, even though the heterogeneity of surface mass flux distribution would become more considerable, the effects of increasing shape deformation to the overall release rate would be less than expected unless the coating film was deformed significantly enough. The effect of the shape deformation and the morphology difference become less effective to differentiate the release characteristics with increasing D(r).

Delayed-Action Preparations↗

PubMed2001

Thermal pyrolysis characteristics of polymer flocculated waste activated sludge.

Polyelectrolyte conditioning is a common practice in wastewater management. This paper experimentally elucidated the thermal pyrolysis characteristics of waste activated sludge at a temperature range of 300-900 K (27-627 degrees C) using thermogravimetric analysis (TGA) in inert atmosphere, with especial attention on the effect of polyelectrolyte flocculation (using cationic polyacrylamide). On the pyrolysis rate vs temperature plot two maxima were noted. At the heating rate of 8 degrees C/min, polyelectrolyte does not influence the pyrolysis process. As higher heating rates (14 and 20 degrees C/min), on the other hand, flocculation to charge neutralization point would enhance the rate of thermal pyrolysis. A simple two parallel-reaction kinetic model is applied to interpret the experimental data. Possible roles of flocculant on sludge pyrolysis are discussed on the basis of change in sludge structures and the hindrance of surface reactions of sludge particles.

Electrolytes↗

PubMed2001

Co-conditioning and dewatering of chemical sludge and waste activated sludge.

The conditioning and dewatering behaviors of chemical and waste activated sludges from a tannery were studied. Capillary suction time (CST), specific resistance to filtration (SRF), and bound water content were used to evaluate the sludge dewatering behaviors. Zeta potentials were also measured. Experiments were conducted on each sludge conditioned and dewatered separately, and on the sludge mixed at various ratios. Results indicate that the chemical sludge was relatively difficult to be dewatered, even in the presence of polyelectrolyte. When the waste activated sludge was mixed with the chemical sludge at ratios of 1:1 and 2:1, respectively, the dewaterability of chemical sludge improved remarkably while the relatively better dewaterability of the waste activated sludge deteriorated only to a limited extent. As the mixing ratios became 4:1 and 8:1, the dewaterability of the mixed sludge was equal to that of the waste activated sludge. The optimal polyelectrolyte dosage for the mixed sludge was equal to or less than that of the waste activated sludge. It is proposed that the chemical sludges act as skeleton builders that reduce the compressibility of the mixed sludge whose dewaterability is enhanced. Bound water contents of sludge decreased at low polyelectrolyte dosage and were not significantly affected as polyelectrolyte dosage increased. Advantages and disadvantages of co-conditioning and dewatering chemical sludge and waste activated sludge were discussed.

Electrolytes↗

PubMed2001

Observations on changes in ultrasonically treated waste-activated sludge.

This work experimentally elucidates the effects of ultrasonic treatment on the physical, chemical, and biological characteristics of a waste-activated sludge. A critical ultrasonic power level exists above which, accompanied with the release of divalent cations from the sludge body, the floc structure effectively disintegrated, microbial level acceptably disinfected, and particulate organic compounds sufficiently transformed into soluble state. Both ultrasonic vibration and bulk temperature rise contribute to the treatment efficiency. Possible mechanisms of ultrasonic treatment are discussed.

Biodegradation, Environmental↗

PubMed2001

Novel cake characteristics of waste-activated sludge.

Breaking down the time limit constraints for conventional compression-permeation (C-P) cell test, this work has, for the first time, experimentally evaluated the cake characteristics of viable waste-activated sludge subject to polyelectrolyte flocculation and to freeze/thaw treatment under a pressure range of 25-200 kPa. There exists a threshold pressure exceeding which the cake structure would significantly deteriorate. Also, the present biological sludge is a "super-compactible" sludge, whose compactibility is greater than most data ever reported in open literature. The information presented herein has implications to filter design/operation and can be used as a reference data set for examining the existing filtration theories.

Bacteria↗

PubMed2001

Experimental analysis of centrifugal dewatering process of polyelectrolyte flocculated waste activated sludge.

The study experimentally investigated the centrifugal separation of moisture from activated sludge subject to cationic polyelectrolyte flocculation. An arm-suspended centrifuge was employed which allowed in-situ detection on all positions of interfaces of centrifuged sludge as functions of time. Experimental results revealed that, sludge flocculation would yield a significant sedimentation effect at the first phase of centrifugation. Therefore, not as suggested in conventional centrifugal-filtration models, the most significant moisture-removal stages included filtrate to flow through a wet cake. Moreover, an optimal rotational speed exists at which the moisture-removal rate reaches a maximum value. New theories/correlations are required to describe centrifugation dewatering of polyelectrolyte flocculated sludge.

Centrifugation↗

PubMed2001

High-speed sludge freezing.

The investigation examined the feasibility of applying a "high-speed freezing technique, using liquid nitrogen freezing, to condition activated sludges and alum sludges. Experimental results indicate that the freezing speed is much faster than that adopted in most previous works on sludge freezing. Although the filterability and settleability of the alum sludge is improved by 3-min liquid nitrogen freezing, no similar improvement is observed for activated sludge. Moreover, curing affects neither sludge after liquid nitrogen freezing, but affects the slow-freezing activated sludge.

Alum Compounds↗

PubMed2001

Hydrodynamic drag on non-spherical floc and free-settling test.

This work numerically investigates the hydrodynamic drag force exerted on a porous spheroid floc moving steadily through a quiescent Newtonian fluid over a wide range of the Reynolds number. The flow patterns for a highly porous spheroid moving at an elevated Reynolds number are basically the same as those at a low Reynolds number, which extends the applicable range of a creeping-flow based correlation to the higher Reynolds number regime. The shape effect becomes more prominent as the spheroid becomes more porous. Using the equivalent diameter, defined as the geometric mean diameter of the principal axes, leads to a universal correlation relating to the drag force, aspect ratio, and interior permeability. In addition, free-settling experiments are performed to estimate how the non-spherical shape affects the three sludge samples. The possible errors in data reduction for the free-settling test are attributed to the a/b ratio and the internal permeability. The errors range from 16-34% for a/b = 0.6-2.0.

Flocculation↗

PubMed2001

Errors in bound water measurements using centrifugal settling method.

Centrifugal settling method (CSM) is commonly used to estimate the bound water content in sludges. The sludge sediment matrix should be purely plastic for accurate measurements to the bound water content. This communication, however, addressed for the first time that, owing to the inhibited elasticity of the sludge matrix, sediment height rebound was commonly observed for the flocculated sludge. Also, different sludges could have distinct elastic responses after centrifugation. There existed no simple correlation to incorporate the elastic rebound of sludge sediment in bound water measurement. The possible errors incorporated into CSM for measuring bound water contents were highlighted.

Centrifugation↗