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1.
Biol Bull ; 241(1): 16-29, 2021 08.
Article in English | MEDLINE | ID: mdl-34436968

ABSTRACT

AbstractNearshore foundation species in coastal and estuarine systems (e.g., salt marsh grasses, mangroves, seagrasses, corals) drive the ecological functions of ecosystems and entire biomes by creating physical structure that alters local abiotic conditions and influences species interactions and composition. The resilience of foundation species and the ecosystem functions they provide depends on their phenotypic and genetic responses to spatial and temporal shifts in environmental conditions. In this review, we explore what is known about the causes and consequences of adaptive genetic differentiation in marine foundation species over spatial scales shorter than dispersal capabilities (i.e., microgeographic scales). We describe the strength of coupling field and laboratory experiments with population genetic techniques to illuminate patterns of local adaptation, and we illustrate this approach by using several foundation species. Among the major themes that emerge from our review include (1) adaptive differentiation of marine foundation species repeatedly evolves along vertical (i.e., elevation or depth) gradients, and (2) mating system and phenology may facilitate this differentiation. Microgeographic adaptation is an understudied mechanism potentially underpinning the resilience of many sessile marine species, and this evolutionary mechanism likely has particularly important consequences for the ecosystem functions provided by foundation species.


Subject(s)
Anthozoa , Ecosystem , Acclimatization , Adaptation, Physiological/genetics , Animals , Biological Evolution
2.
Article in English | MEDLINE | ID: mdl-33746555

ABSTRACT

The use of air sensor technology is increasing worldwide for a variety of applications, however, with significant variability in data quality. The United States Environmental Protection Agency held a workshop in July 2019 to deliberate possible performance targets for air sensors measuring particles with aerodynamic diameters of 10 µm or less (PM10), nitrogen dioxide (NO2), carbon monoxide (CO), and sulfur dioxide (SO2). These performance targets were discussed from the perspective of non-regulatory applications and with the sensors operating primarily in a stationary mode in outdoor environments. Attendees included representatives from multiple levels of government organizations, sensor developers, environmental nonprofits, international organizations, and academia. The workshop addressed the current lack of sensor technology requirements, discussed fit-for-purpose data quality needs, and debated transparency issues. This paper highlights the purpose and key outcomes of the workshop. While more information on performance and applications of sensors is available than in past years, the performance metrics, or parameters used to describe data quality, vary among the studies reports and there is a need for more clear and consistent approaches for evaluating sensor performance. Organizations worldwide are increasingly considering, or are in the process of developing, sensor performance targets and testing protocols. Workshop participants suggested that these new guidelines are highly desirable, would help improve data quality, and would give users more confidence in their data. Given the wide variety of uses for sensors and user backgrounds, as well as varied sensor design features (e.g., communication approaches, data tools, processing/adjustment algorithms and calibration procedures), the need for transparency was a key workshop theme. Suggestions for increasing transparency included documenting and sharing testing and performance data, detailing best practices, and sharing data processing and correction approaches.

3.
JRSM Open ; 9(10): 2054270418793029, 2018 Oct.
Article in English | MEDLINE | ID: mdl-30302265

ABSTRACT

Immunotherapy is now being routinely used in the management of many cancers. It is therefore vital that all clinicians are aware of the diverse array of cutaneous manifestations that can result from their use, which can vary from mild to life threatening.

4.
J R Army Med Corps ; 163(5): 311-318, 2017 Oct.
Article in English | MEDLINE | ID: mdl-28356493

ABSTRACT

INTRODUCTION: Women in the military are a minority group who, in addition to facing exposure to traumatic events due to the nature of the work, face additional stressors while deployed. It is argued that these exposures and experiences place individuals at a significantly higher risk of finding it difficult adjusting post deployment. This paper focuses on the psychological health and well-being of female veterans post-deployment. METHODS: A systematic review of the literature related to female veterans' experiences upon returning home from deployment was conducted. RESULTS: Eight in-depth qualitative studies met the inclusion criteria for the study and were analysed using thematic analysis. Five key themes were identified in the papers: (1) bringing the war home, (2) post-deployment adjustment, (3) loss, (4) failed belongingness and (5) post-traumatic growth. CONCLUSIONS: These studies provide a useful insight into the different psychological health and well-being experiences that female veterans encounter. Additionally, the associated effects upon the individual and their families and communities are considered.


Subject(s)
Mental Health/statistics & numerical data , Veterans/psychology , Veterans/statistics & numerical data , Adult , Female , Humans , Qualitative Research , Young Adult
5.
Chem Commun (Camb) ; 51(57): 11433-6, 2015 Jul 21.
Article in English | MEDLINE | ID: mdl-26086156

ABSTRACT

Hybrid materials which selectively extract Am(III) over Eu(III) from 0.01 M nitric acid solutions with fast kinetics and separation factors up to 160 have been synthesised. The materials consist of titania functionalised with a modified organic 2,6-bis(1,2,4-triazin-3-yl)pyridine (BTP) derivative. Both particles and hierarchically porous beads have been prepared and provide advantages over conventional solvent extraction separations.

6.
Chem Commun (Camb) ; 51(58): 11726, 2015 Jul 25.
Article in English | MEDLINE | ID: mdl-26114605

ABSTRACT

Correction for 'Effective Am(III)/Eu(III) separations using 2,6-bis(1,2,4-triazin-3-yl)pyridine (BTP) functionalised titania particles and hierarchically porous beads' by J. Veliscek-Carolan et al., Chem. Commun., 2015, DOI: 10.1039/c5cc03957f.

7.
J Control Release ; 165(1): 16-21, 2013 Jan 10.
Article in English | MEDLINE | ID: mdl-23142776

ABSTRACT

New generation vaccines increasingly utilize highly purified peptides and proteins as the target antigen, however these are often poorly immunogenic. One of the most promising strategies for improving immunogenicity of such subunit vaccines is through incorporation into particulate carriers. Here we report the preparation, physicochemical characterization and in vivo immunological activity of cubosomes, a novel lipid-based nanostructured particulate carrier, modified to include the Toll-like receptor agonists monophosphoryl lipid A and imiquimod. The immunological activity of cubosome formulations was compared to that of liposome and alum formulations. Sustained release of the model antigen ovalbumin (Ova) was observed in vitro and in vivo from cubosomes. Cubosomes+adjuvants induced robust CD8⁺ and CD4⁺ T cell proliferation and interferon-γ production, as well as the production of Ova-specific antibodies. Cubosomes+adjuvants were more efficient at generating Ova-specific cellular responses and were equally as effective in generating humoral responses when compared to liposomes+adjuvants and alum. Overall, the results show that cubosomes have the potential to act as effective sustained release vaccine delivery systems.


Subject(s)
Adjuvants, Immunologic/administration & dosage , Aminoquinolines/administration & dosage , Drug Delivery Systems , Lipid A/analogs & derivatives , Nanostructures/administration & dosage , Adjuvants, Immunologic/chemistry , Aminoquinolines/chemistry , Animals , Antigens/administration & dosage , CD4-Positive T-Lymphocytes/drug effects , CD4-Positive T-Lymphocytes/immunology , CD8-Positive T-Lymphocytes/drug effects , CD8-Positive T-Lymphocytes/immunology , Female , Imiquimod , Immunity, Cellular/drug effects , Immunity, Humoral/drug effects , Lipid A/administration & dosage , Lipid A/chemistry , Male , Mice , Mice, Inbred C57BL , Mice, Transgenic , Nanostructures/chemistry , Ovalbumin/administration & dosage , Vaccines/administration & dosage
8.
Reprod Toxicol ; 34(3): 331-9, 2012 Nov.
Article in English | MEDLINE | ID: mdl-22677474

ABSTRACT

The extended one-generation reproduction toxicity study (OECD 443, adopted 28-July-2011) produces more information with fewer animals than the two-generation study (OECD 416), by including F1 neurotoxicity and immunotoxicity assessments, and omitting an F2 generation if there are no relevant F1 findings. This saves >1000 animals per compound. Feasibility studies based on draft OECD443 were conducted in industrial GLP laboratories in Europe and USA, using vinclozolin, methimazole and lead acetate. A fourth study was conducted with 2,4-dichlorophenoxyacetic acid (2,4-D) in response to a regulatory request for reproduction and developmental neurotoxicity data. The studies effectively profiled vinclozolin as an anti-androgenic developmental toxicant, methimazole as a developmental anti-thyroid agent, and lead acetate as a systemic and developmental toxicant. The 2,4-D study demonstrated the value of toxicokinetic data in dose setting and data interpretation. These results illustrate the variety of reproductive and developmental endpoints which can be captured in this complex but manageable study design. Time constraints for triggering further (F2) testing are summarized.


Subject(s)
Animal Use Alternatives , Hazardous Substances/toxicity , Reproduction/drug effects , Toxicity Tests/methods , 2,4-Dichlorophenoxyacetic Acid/toxicity , Androgen Antagonists/toxicity , Animals , Antithyroid Agents/toxicity , Female , Immune System/drug effects , Male , Methimazole/toxicity , Neurotoxicity Syndromes/etiology , Organometallic Compounds/toxicity , Oxazoles/toxicity , Rats , Rats, Sprague-Dawley , Rats, Wistar
9.
Eur J Pharm Biopharm ; 79(1): 15-22, 2011 Sep.
Article in English | MEDLINE | ID: mdl-21237267

ABSTRACT

Different delivery strategies to improve the immunogenicity of peptide/protein-based vaccines are currently under investigation. In this study, the preparation and physicochemical characterisation of cubosomes, a novel lipid-based particulate system currently being explored for vaccine delivery, was investigated. Cubosomes were prepared from a liquid precursor mixture containing phytantriol or glycerylmonooleate (GMO), F127 for particle stabilisation, and a hydrotrope (ethanol or polyethylene glycol (PEG(200)) or propylene glycol (PG)). Several liquid precursors were prepared, and the effect of varying the concentrations of F127 and the hydrotrope on cubosome formation was investigated. Formulations were prepared by fragmentation for comparison. The model protein ovalbumin (Ova) was also entrapped within selected formulations. Submicron-sized particles (180-300 nm) were formed spontaneously upon dilution of the liquid precursors, circumventing the need for the preformed cubic phase used in traditional fragmentation-based methods. The nanostructure of the phytantriol dispersions was determined to be cubic phase using SAXS whilst GMO dispersions had a reverse hexagonal nanostructure coexisting with cubic phase. The greatest entrapment of Ova was within phytantriol cubosomes prepared from liquid precursors. Release of Ova from the various formulations was sustained; however, release was significantly faster and the extent of release was greater from fragmented dispersions compared to liquid precursor formulations. Taken together, these results suggest that phytantriol cubosomes can be prepared using liquid precursors and that it is a suitable alternative to GMO. Furthermore, the high entrapment and the slow release of Ova in vitro highlight the potential of phytantriol cubosomes prepared using liquid precursors as a novel vaccine delivery system.


Subject(s)
Drug Delivery Systems , Excipients/chemistry , Fatty Alcohols/chemistry , Nanostructures/administration & dosage , Vaccines/administration & dosage , Delayed-Action Preparations , Drug Compounding , Drug Evaluation, Preclinical , Ethanol/chemistry , Fatty Alcohols/chemical synthesis , Glycerides/chemistry , Glycerides/metabolism , Humans , Lipids/chemistry , Nanostructures/chemistry , Ovalbumin/administration & dosage , Ovalbumin/chemistry , Particle Size , Polyethylenes/chemistry , Polyethylenes/metabolism , Polypropylenes/chemistry , Polypropylenes/metabolism , Proteins/administration & dosage , Proteins/chemistry , Proteins/immunology , Solvents/chemistry , Vaccines/chemistry , Vaccines/immunology
10.
J Pharm Sci ; 98(11): 4191-204, 2009 Nov.
Article in English | MEDLINE | ID: mdl-19340889

ABSTRACT

Swelling and phase behaviour of phytantriol and glyceryl monooleate (GMO) matrices with varying water loadings were investigated. Release of a model protein, FITC-Ova was subsequently examined. Polarised light microscopy and small angle X-ray scattering analysis showed that the addition of FITC-Ova only altered the liquid crystalline structure of phytantriol matrices at low water loadings, and that postrelease study, the phase structure of matrices at both low and high loading reflected that of the binary system. Addition of FITC-Ova to GMO matrices also altered the liquid crystalline structure when compared to the respective binary system at low but not at high loading. All samples analysed after the release study had transformed to the reverse hexagonal phase (H(II)). Swelling studies revealed a faster and more extensive swelling of GMO when compared to phytantriol. Release of FITC-Ova from phytantriol matrices was faster and occurred to a greater extent most likely due to the conversion of GMO matrices into the H(II) phase. No effect on release as a function of initial water content was observed for either lipid. We have confirmed that phytantriol based liquid crystalline matrices can sustain the release of a hydrophilic protein, suggesting its suitability as a potential sustained antigen-delivery system.


Subject(s)
Fatty Alcohols/chemistry , Glycerides/chemistry , Liquid Crystals/chemistry , Nanostructures/chemistry , Phase Transition , Fluorescein-5-isothiocyanate/metabolism , Fluorescent Dyes/metabolism , Kinetics , Liquid Crystals/ultrastructure , Microscopy, Polarization , Molecular Structure , Scattering, Small Angle , Water/chemistry , X-Ray Diffraction
11.
Toxicol Sci ; 67(1): 144-52, 2002 May.
Article in English | MEDLINE | ID: mdl-11961227

ABSTRACT

Spinosad, an insecticide derived from a naturally occurring bacterium via fermentation, represents a new class of insecticides acting by a novel mode of action. A dietary study was conducted in Sprague-Dawley rats in which groups of 30 rats/sex/dosage level were given diets that provided 0, 3, 10, or 100 mg spinosad/kg body weight/day, 7 days/week, for 2 successive generations. Following 10 weeks of dietary exposure, the P1 generation was mated twice to produce F1a and F1b litters. After weaning, groups of 30 rats/sex/dosage level were selected from the F1a litters, given diets containing spinosad for 12 weeks, and mated to produce the F2 generation. Dietary administration of spinosad to rats at a dosage of 100 mg/kg/day over 2 generations produced parental toxicity and effects on the offspring. Among adult males, body weights and weight gains were decreased 2-9% relative to controls, with P1 males more affected than P2. Absolute and relative liver, kidney, heart, spleen, and thyroid weights were increased by from 12% to as much as 240% of control values. Histologic changes consistent with cationic amphiphilic compounds were noted in the kidneys, lungs, mesenteric lymph nodes, spleen, and thyroid of P1 and P2 males and females. In females given 100 mg/kg/day, though premating body weights were not affected, weight gains during the F1a and F1b gestation periods were depressed 15-16%. Increased incidences of dystocia, and vaginal bleeding and mortality occurred during parturition and lactation at 100 mg/kg/day. Effects on the offspring (decreased litter size and survival through day 4 of lactation) were limited to the high-dosage group. Signs indicative of poor maternal care noted in the pups (stomachs void of milk, cold, thin, etc.) were observed at 100 mg/kg/day. Early postnatal effects on the offspring were considered likely secondary to the effects in maternal animals around the time of parturition. At 100 mg/kg/day, weight gain in pups was depressed throughout lactation, with statistically significantly decreased weights noted toward the latter half of the lactation period. There were no treatment-related effects on adults or their offspring at 3 or 10 mg/kg/day in either generation. Based on these results, spinosad is not considered a selective reproductive toxicant, (i.e., no effects on reproductive parameters were noted below a level that produced toxicity in the adults) and the no observed effect level (NOEL) for both parental and reproductive/perinatal toxicity was 10 mg/kg/day.


Subject(s)
Insecticides/toxicity , Macrolides/toxicity , Prenatal Exposure Delayed Effects , Reproduction/drug effects , Animals , Animals, Newborn , Body Weight/drug effects , Dose-Response Relationship, Drug , Drug Combinations , Female , Longevity/drug effects , Male , Organ Size/drug effects , Pregnancy , Rats , Rats, Sprague-Dawley , Toxicity Tests , Weight Gain/drug effects
12.
Toxicol Sci ; 60(1): 121-31, 2001 Mar.
Article in English | MEDLINE | ID: mdl-11222879

ABSTRACT

The potential for 2,4-D and its salts and esters to induce developmental toxicity was investigated in rats (8 studies) and rabbits (7 studies). Maternal toxicity associated with exposure was dependent on the dose level expressed as 2,4-D acid equivalents. The severity of the maternal effect was correlated to the 2,4-D acid-equivalent dose, with increasing dose levels that exceeded renal clearance causing increasingly more severe maternal effects. In both species, maternal body weight effects began to be manifested at dose levels of 30 mg 2,4-D acid equivalent/kg/day. At higher dose levels (50-75 mg/kg/day in rats and 75-90 mg/kg/day in rabbits), body weights and feed consumption were more severely affected. At dose levels > or =90 mg/kg/day in rats, clinical signs of toxicity (ataxia, muscular stiffness, and decreased motor activity) and mortality were noted. The no-observed-adverse-effect level (NOAEL) for maternal toxicity in both species across the family of 2,4-D salts and esters was approximately 10 mg/kg/day. Significantly decreased fetal body weights and increased fetal variations were seen in rats only at maternally toxic dose levels in excess of 90 mg/kg/day acid equivalent. At maternally toxic doses in rabbits, embryonal and fetal development were essentially unaffected. There were no effect on maternal reproductive measures such as litter size, resorption rates, or fetal body weights, and there was no evidence of teratogenic activity. In summary, equivalent toxicity of the salts and esters is consistent with rapid and complete metabolic conversion to 2,4-D acid. No adverse fetal effects were noted at dose levels that did not also produce evidence of maternal toxicity or exceed renal clearance of 2,4-D indicating that the developing rat and rabbit fetus were not uniquely sensitive to 2,4-D and its forms.


Subject(s)
2,4-Dichlorophenoxyacetic Acid/toxicity , Abnormalities, Drug-Induced , Teratogens/toxicity , 2,4-Dichlorophenoxyacetic Acid/analogs & derivatives , Animals , Ataxia/chemically induced , Body Weight/drug effects , Dose-Response Relationship, Drug , Eating/drug effects , Embryo, Mammalian/drug effects , Female , Fetal Weight/drug effects , Male , Maternal Exposure , Motor Activity/drug effects , No-Observed-Adverse-Effect Level , Pliability/drug effects , Pregnancy , Rabbits , Rats
14.
Toxicol Sci ; 57(2): 250-63, 2000 Oct.
Article in English | MEDLINE | ID: mdl-11006355

ABSTRACT

Pregnant Sprague-Dawley rats were given chlorpyrifos (O:, O-diethyl-O:-[3,5,6-trichloro-2-pyridinyl] phosphorothioate; CPF) in corn oil by gavage from gestation day 6 (GD 6) through lactation day 10 (LD 10) at dosages of 0, 0.3, 1, or 5 mg/kg/day in a developmental neurotoxicity study that conformed to U.S. Environmental Protection Agency 1991 guidelines. GD 0 was the day when evidence of mating was observed and postnatal day 0 (PND 0) was the day of birth. Toxicity was limited to the highest dosage level (5 mg/kg/day) and, in the dams, consisted of muscle fasciculation, hyperpnea, and hyperreactivity. A nonsignificant overall trend toward weight gain and feed consumption was also observed in the high-dosage dams, with a statistically significant Group x Time interaction for reduced weight gain in the 5-mg/kg/day group near the end of gestation. Although many developmental indices were normal, pups from high-dosage dams had increased mortality soon after birth, gained weight more slowly than controls, and had several indications of slightly delayed maturation. The early deaths and delayed maturation were attributed to maternal toxicity, though a possible contributing role of direct pup toxicity in delayed development cannot be eliminated. In spite of the apparent delay in physical development, high-dosage pups tested just after weaning had normal learning and memory as tested on a T-maze spatial delayed-alternation task. Habituation, a primitive form of learning, was tested in 2 tasks (motor activity and auditory startle) and was not affected. No overt effects were noted in either dams or pups at 1 or 0.3 mg/kg/day. Based on these data, chlorpyrifos produced maternal and developmental toxicity in the 5-mg/kg/day-dosage group. There was no evidence of selective developmental neurotoxicity following exposure to chlorpyrifos.


Subject(s)
Brain/drug effects , Chlorpyrifos/toxicity , Insecticides/toxicity , Nervous System Malformations/chemically induced , Prenatal Exposure Delayed Effects , Administration, Oral , Animals , Animals, Newborn/growth & development , Animals, Suckling/growth & development , Behavior, Animal/drug effects , Body Weight/drug effects , Brain/abnormalities , Chlorpyrifos/administration & dosage , Cholinesterases/blood , Cognition/drug effects , Female , Insecticides/administration & dosage , Male , Maternal Exposure , Maze Learning/drug effects , Memory/drug effects , Motor Activity/drug effects , Nervous System Malformations/pathology , Organ Size/drug effects , Pregnancy , Rats , Rats, Sprague-Dawley , Reflex, Startle/drug effects , Space Perception/drug effects , Toxicity Tests
15.
Toxicol Sci ; 53(1): 100-8, 2000 Jan.
Article in English | MEDLINE | ID: mdl-10653527

ABSTRACT

3,5,6-Trichloro-2-pyridinol (TCP), the primary metabolite of chlorpyrifos and chlorpyrifos-methyl, was evaluated for potential developmental toxicity. Groups of 32-34 bred female Fischer 344 rats were given 0, 50, 100, or 150 mg TCP/kg/day by gavage on gestation days 6-15; the fetuses were evaluated on gestation day 21. Similarly, groups of 16 inseminated female New Zealand White rabbits were given 0, 25, 100, or 250 mg TCP/kg/day by gavage on gestation days 7-19, and fetuses were evaluated on gestation day 28. No clinical signs of toxicity attributed to TCP were noted in either species. In rats, at 150 mg/kg/day, maternal effects included slight decreases in feed consumption, significantly depressed body weight gain (25% relative to controls) resulting in significantly lower maternal terminal body weights, and increased relative liver weight. At 100 mg/kg/day, maternal body weight gain in rats was depressed approximately 22%. Among rabbits, maternal effects were limited to the group given 250 mg/kg/day, which lost an average of approximately 70 g during the treatment period (vs. 140 g in the controls). There were no effects on fetal weight or viability, nor were there significant increases in any fetal alteration in either species. A slightly higher (not statistically significant) than usual incidence of central nervous system anomalies occurred in rabbits, but these anomalies were found in both treated and control groups in this study as well as contemporaneous studies of unrelated compounds. This, and the fact that these anomalies were not seen with the parent compound, chlorpyrifos, suggest that their origin was spontaneous. Thus, TCP was not considered fetotoxic or teratogenic in either rats or rabbits, even at dose levels that produced maternal toxicity.


Subject(s)
Abnormalities, Drug-Induced/etiology , Herbicides/toxicity , Pyridones/toxicity , Animals , Body Weight/drug effects , Cerebral Ventricles/abnormalities , Cerebral Ventricles/drug effects , Female , Fetal Viability/drug effects , Herbicides/chemistry , Hydrocephalus/chemically induced , Liver/drug effects , Liver/pathology , Male , Pregnancy , Pyridones/chemistry , Rabbits , Rats , Rats, Inbred F344 , Reproduction/drug effects , Toxicity Tests , Weight Gain/drug effects
17.
Appl Biochem Biotechnol ; 77-79: 473-84, 1999.
Article in English | MEDLINE | ID: mdl-15304716

ABSTRACT

Phenyl ethyl alcohol is a compound that occurs naturally in flower petals and in many common beverages, such as beer. Desire for the floral, rose-like notes imparted by phenyl ethyl alcohol has created a unique niche for this chemical in flavor and fragrance industries. Phenyl ethyl alcohol can be produced by Saccharomyces cerevisiae via bioconversion. Often this method of production results in extremely low yields, thus placing a great deal of importance on recovery and purification of the valuable metabolite. To determine the best method for recovering the chemical, a primary recovery step and a secondary recovery step were developed. The primary recovery step consisted of comparing dead-end filtration with crossflow ultrafiltration. Crossflow ultrafiltration was ultimately selected to filter the fermentation broth because of its high flow rates and low affinity for the product. The secondary recovery step consisted of a comparison of liquid- liquid extraction and hydrophobic resin recovery. The hydrophobic resin was selected because of its higher rate of recovery and a higher purity than the liquid-liquid extraction, the current practice of Brown-Forman.

18.
Appl Biochem Biotechnol ; 70-72: 615-27, 1998.
Article in English | MEDLINE | ID: mdl-18576026

ABSTRACT

Variations to the original aeration system in a continuous roller bottle reactor of novel design have been tested and compared for optimal oxygen (O) delivery. Reactor operating parameters that affect O transfer are rotation rate, liquid-volume level, fresh-feed rate, and supplementary-aeration rate. Design modifications to enhance gas-liquid O transfer include the addition of wall baffles and center baffles. The number and location of each of these baffles are compared for their effect on k(L)a values in the reaction chamber. The liquid feed into the system has been modified to improve the axial liquid mixing and O transfer.

19.
Appl Biochem Biotechnol ; 63-65: 363-73, 1997.
Article in English | MEDLINE | ID: mdl-18576095

ABSTRACT

Volumetric gas-liquid mass transfer coefficients were measured in suspensions of cellulose fibers with concentrations ranging from 0 to 20 g/L. The mass transfer coefficients were measured using the dynamic method. Results are presented for three different combinations of impellers at a variety of gassing rates and agitation speeds. Rheological properties of the cellulose fibers were also measured using the impeller viscometer method. Tests were conducted in a 20 L stirred-tank fermentor and in 65 L tank with a height to diameter ratio of 3:1. Power consumption was measured in both vessels. At low agitation rates, two Rushton turbines gave 20% better performance than the Rushton and hydrofoil combination and 40% better performance than the Rushton and propeller combination for oxygen transfer. At higher agitation rates, the Rushton and hydrofoil combination gave 14 and 25% better performance for oxygen transfer than two Rushton turbines and the Rushton and hydrofoil combination, respectively.

20.
Appl Biochem Biotechnol ; 63-65: 375-85, 1997.
Article in English | MEDLINE | ID: mdl-18576096

ABSTRACT

The impeller viscometer technique is frequently used to characterize the rheology of filamentous suspensions in order to avoid difficulties encountered with conventional instruments. This work presents the results of experiments conducted with vane, turbine, and helical impellers. The validity of the assumptions made in the determination of the torque and shear-rate constants were assessed for each impeller type. For the turbine and vane impellers, an increase in the apparent torque constant c was observed with increasing Reynolds number even when measurements were confined to the viscous regime. The shear-rate constants determined for the vane and turbine impellers varied for different calibration fluids, which contradicts the assumptions usually invoked in the analysis of data for this technique. When the helical impeller was calibrated, consistent values for the torque and shear-rate constants were obtained. The three impeller types were also used to characterize the rheology of cellulose fiber suspensions and the results compared for consistency and reproducibility. The results have application in design of rheometers for use in process control and product quality assessment in the fermentation and pulp and paper industries.

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