			Home About us Contact

Set Point (set + point)

Distribution by Scientific Domains

Medical Sciences	27%
Engineering	27%
Chemistry	22%
Life Sciences	18%

Selected Abstracts

A cost-effective operating strategy to reduce energy consumption in a HVAC system

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2008
Nabil Nassif
Abstract The operation of the building heating, ventilating, and air conditioning (HVAC) system is a critical activity in terms of optimizing the building's energy consumption, ensuring the occupants' comfort, and preserving air quality. The performance of HVAC systems can be improved through optimized supervisory control strategies. Set points can be adjusted by the optimized supervisor to improve the operating efficiency. This paper presents a cost-effective building operating strategy to reduce energy costs associated with the operation of the HVAC system. The strategy determines the set points of local-loop controllers used in a multi-zone HVAC system. The controller set points include the supply air temperature, the supply duct static pressure, and the chilled water supply temperature. The variation of zone air temperatures around the set point is also considered. The strategy provides proper set points to controllers for minimum energy use while maintaining the required thermal comfort. The proposed technology is computationally simple and suitable for online implementation; it requires access to some data that are already measured and therefore available in most existing building energy management and control systems. The strategy is evaluated for a case study in an existing variable air volume system. The results show that the proposed strategy may be an excellent means of reducing utility costs associated with maintaining or improving indoor environmental conditions. It may reduce energy consumption by about 11% when compared with the actual strategy applied on the investigated existing system. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Epigenetic control of translation regulation: Alterations in histone H3 lysine 9 post-translation modifications are correlated with the expression of the translation initiation factor 2B (Eif2b5) during thermal control establishment

DEVELOPMENTAL NEUROBIOLOGY, Issue 2 2010
Tatiana Kisliouk
Abstract Thermal control set point is regulated by thermosensitive neurons of the preoptic anterior hypothalamus (PO/AH) and completes its development during postnatal critical sensory period. External stimuli, like increase in environmental temperature, influence the neuronal protein repertoire and, ultimately, cell properties via activation or silencing of gene transcription, both of which are regulated by the "histone code."" Here, we demonstrated an increase in global histone H3 lysine 9 (H3K9) acetylation as well as H3K9 dimethylation in chick PO/AH during heat conditioning at the critical period of sensory development. In contrast to the global profile of H3K9 modifications, acetylation and dimethylation patterns of H3K9 at the promoter of the catalytic subunit of eukaryotic translation initiation factor 2B (Eif2b5) were opposite to each other. During heat conditioning, there was an increase in H3K9 acetylation at the Eif2b5 promoter, simultaneously with decrease in H3K9 dimethylation. These alterations coincided with Eif2b5 mRNA induction. Moreover, exposure to excessive heat during the critical period resulted in long-term effect on both H3K9 tagging at the Eif2b5 promoter and Eif2b5 mRNA expression. These data suggest a role for dynamic H3K9 post-translational modifications in global translation regulation during the thermal control establishment. © 2009 Wiley Periodicals, Inc. Develop Neurobiol, 2010 [source]

Modeling complex decay profiles of hepatitis B virus during antiviral therapy,,

HEPATOLOGY, Issue 1 2009
Harel Dahari
Typically, hepatitis B virus (HBV) decays in patients under therapy in a biphasic manner. However, more complex decay profiles of HBV DNA (e.g., flat partial response, triphasic, and stepwise), for which we have no clear understanding, have also been observed in some treated patients. We recently introduced the notion of a critical drug efficacy, ,c, such that if overall drug efficacy, ,tot, is higher than the critical drug efficacy (i.e., ,tot > ,c) then viral levels will continually decline on therapy, while if ,tot < ,c, then viral loads will initially decline but will ultimately stabilize at a new set point, as seen in flat partial responders. Using the idea of critical efficacy and including hepatocyte proliferation in a viral kinetic model, we can account for these complex HBV DNA decay profiles. The model predicts that complex profiles such as those exhibiting a plateau or shoulder phase, as well as a class of stepwise declines, occur only in patients in whom the majority of hepatocytes are infected before therapy. Conclusion: We show via kinetic modeling how a variety of HBV DNA decay profiles can arise in treated patients. (HEPATOLOGY 2009;49:32-38.) [source]

Experimental modelling and intelligent control of a wood-drying kiln

INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 8 2001
Givon Chuen Kee Yan
Abstract Proper control of the wood-drying kiln is crucial in ensuring satisfactory quality of dried wood and in minimizing drying time. This paper presents the development, implementation, and evaluation of a control system for a lumber drying kiln process incorporating sensory feedback from in-wood moisture content sensors and intelligent control such that the moisture content of lumber will reach and stabilize at the desired set point without operator interference. The drying process is difficult to model and control due to complex dynamic nonlinearities, coupling effects among key variables, and process disturbances caused by the variation of lumber sizes, species, and environmental factors. Through system identification scheme using experimental data and recursive least-squares algorithm for parameter estimation, appropriate models are developed for simulation purpose and controller design. Two different control methodologies are employed and compared: a conventional proportional-integral-derivative (PID) controller and a direct fuzzy logic controller (FLC), and system performance is evaluated through simulations. The developed control system is then implemented in a downscaled industrial kiln located at the Innovation Centre of National Research Council (NRC) of Canada. This experimental set-up is equipped with a variety of sensors, including thermocouples for temperature feedback, an air velocity transmitter for measuring airflow speed in the plenum, relative humidity sensors for measuring the relative humidity inside the kiln, and in-wood moisture content sensors for measuring the moisture content of the wood pieces. For comparison, extensive experimental studies are carried out on-line using the two controllers, and the results are evaluated to tune the controller parameters to achieve good performance in the wood-drying kiln. The combination of conventional control with the intelligent control promises improved performance. The control system developed in this study may be applied in industrial wood-drying kilns, with a clear potential for improved quality and increased speed of drying. Copyright © 2001 John Wiley & Sons, Ltd. [source]

A cost-effective operating strategy to reduce energy consumption in a HVAC system

Robust discontinuous exponential regulation of dynamic nonholonomic wheeled mobile robots with parameter uncertainties

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 9 2008
B. L. Ma
Abstract For regulating a dynamic nonholonomic WMR (wheeled mobile robot) with parameter uncertainties, we derive a simple robust discontinuous control law, yielding a global exponential convergence of position and orientation to the desired set point despite parameter uncertainties. The controller design relies on separating the error dynamics into two subsystems, followed by robust feedback control laws to stabilize the subsystems. The effectiveness of the proposed control laws is verified by simulation. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Optimal Body Temperature in Transitional Extremely Low Birth Weight Infants Using Heart Rate and Temperature as Indicators

JOURNAL OF OBSTETRIC, GYNECOLOGIC & NEONATAL NURSING, Issue 1 2010
Robin B. Knobel
ABSTRACT Objective: To explore body temperature in relationship to heart rate in extremely low birth weight (ELBW) infants during their first 12 hours to help identify the ideal set point for incubator control of body temperature. Design: Within subject, multiple-case design. Setting: A tertiary neonatal intensive care unit (NICU) in North Carolina. Participants: Ten infants born at fewer than 29 weeks gestation and weighing 400 to 1,000 g. Methods: Heart rate and abdominal body temperature were measured at 1-minute intervals for 12 hours. Heart rates were considered normal if they were between the 25th and 75th percentile for each infant. Results: Abdominal temperatures were low throughout the 12-hour study period (mean 35.17-36.68 °C). Seven of 10 infants had significant correlations between abdominal temperature and heart rate. Heart rates above the 75th percentile were associated with low and high abdominal temperatures; heart rates less than the 25th percentile were associated with very low abdominal temperatures. The extent to which abdominal temperature was abnormally low was related to the extent to which the heart rate trended away from normal in 6 of the 10 infants. Optimal temperature control point that maximized normal heart rate observations for each infant was between 36.8 °C and 37 °C. Conclusions: Hypothermia was associated with abnormal heart rates in transitional ELBW infants. We suggest nurses set incubator servo between 36.8 °C and 36.9 °C to optimally control body temperature for ELBW infants. [source]

Backstepping-based cascade control scheme for batch distillation columns

AICHE JOURNAL, Issue 9 2004
Rosendo Monroy-Loperena
Abstract Nonstationary dynamics, finite-time operation, large thermodynamical uncertainty and delayed composition measurements make the control of batch distillation processes a challenging and interesting problem. In this paper, a cascade control design to regulate the overhead composition of a batch distillation column is presented. The controller is designed within the framework of robust nonlinear control with modeling error compensation techniques in conjunction with a backstepping approach. The result is a cascade controller with a master loop that, driven by the composition regulation error, produces a time-varying set point for the temperature in a certain tray; and with a secondary controller that manipulates the internal reflux ratio to track the time-varying set point determined by the master composition loop. How to extend the controller design to have multiple slave temperature controllers, to improve the regulation of the overhead composition in a batch distillation column, is also presented. The proposed control approach is illustrated by numerical simulations on a full dynamical model. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2113,2129, 2004 [source]

Robust H, glucose control in diabetes using a physiological model

AICHE JOURNAL, Issue 12 2000
Robert S. Parker
A robust H, controller was developed to deliver insulin via a mechanical pump in Type I diabetic patients. A fundamental nonlinear diabetic patient model was linearized and then reduced to a third-order linear form for controller synthesis. Uncertainty in the nonlinear model was characterized by up to ±40% variation in eight physiological parameters. A sensitivity analysis identified the three-parameter set having the most significant effect on glucose and insulin dynamics over the frequency range of interest , = [0.002, 0.2] (rad/min). This uncertainty was represented in the frequency domain and incorporated in the controller design. Controller performance was assessed in terms of its ability to track a normoglycemic set point (81.1 mg/dL) in response to a 50 g meal disturbance. In the nominal continuous-time case, the controller maintained glucose concentrations within ±3.3 mg/dL of set point. A controller tuned to accommodate uncertainty yielded a maximum deviation of 17.6 mg/dL for the worst-case parameter variation. [source]

A Comparison of Eight Methods for the Dual-Endpoint Evaluation of Efficacy in a Proof-of-Concept HIV Vaccine Trial

BIOMETRICS, Issue 3 2006
Devan V. Mehrotra
Summary To support the design of the world's first proof-of-concept (POC) efficacy trial of a cell-mediated immunity-based HIV vaccine, we evaluate eight methods for testing the composite null hypothesis of no-vaccine effect on either the incidence of HIV infection or the viral load set point among those infected, relative to placebo. The first two methods use a single test applied to the actual values or ranks of a burden-of-illness (BOI) outcome that combines the infection and viral load endpoints. The other six methods combine separate tests for the two endpoints using unweighted or weighted versions of the two-part z, Simes', and Fisher's methods. Based on extensive simulations that were used to design the landmark POC trial, the BOI methods are shown to have generally low power for rejecting the composite null hypothesis (and hence advancing the vaccine to a subsequent large-scale efficacy trial). The unweighted Simes' and Fisher's combination methods perform best overall. Importantly, this conclusion holds even after the test for the viral load component is adjusted for bias that can be introduced by conditioning on a postrandomization event (HIV infection). The adjustment is derived using a selection bias model based on the principal stratification framework of causal inference. [source]

A predictive high-throughput scale-down model of monoclonal antibody production in CHO cells

BIOTECHNOLOGY & BIOENGINEERING, Issue 6 2009
Rachel Legmann
Abstract Multi-factorial experimentation is essential in understanding the link between mammalian cell culture conditions and the glycoprotein product of any biomanufacturing process. This understanding is increasingly demanded as bioprocess development is influenced by the Quality by Design paradigm. We have developed a system that allows hundreds of micro-bioreactors to be run in parallel under controlled conditions, enabling factorial experiments of much larger scope than is possible with traditional systems. A high-throughput analytics workflow was also developed using commercially available instruments to obtain product quality information for each cell culture condition. The micro-bioreactor system was tested by executing a factorial experiment varying four process parameters: pH, dissolved oxygen, feed supplement rate, and reduced glutathione level. A total of 180 micro-bioreactors were run for 2 weeks during this DOE experiment to assess this scaled down micro-bioreactor system as a high-throughput tool for process development. Online measurements of pH, dissolved oxygen, and optical density were complemented by offline measurements of glucose, viability, titer, and product quality. Model accuracy was assessed by regressing the micro-bioreactor results with those obtained in conventional 3,L bioreactors. Excellent agreement was observed between the micro-bioreactor and the bench-top bioreactor. The micro-bioreactor results were further analyzed to link parameter manipulations to process outcomes via leverage plots, and to examine the interactions between process parameters. The results show that feed supplement rate has a significant effect (P,<,0.05) on all performance metrics with higher feed rates resulting in greater cell mass and product titer. Culture pH impacted terminal integrated viable cell concentration, titer and intact immunoglobulin G titer, with better results obtained at the lower pH set point. The results demonstrate that a micro-scale system can be an excellent model of larger scale systems, while providing data sets broader and deeper than are available by traditional methods. Biotechnol. Bioeng. 2009; 104: 1107,1120. © 2009 Wiley Periodicals, Inc. [source]

Exercise-induced hyperthermia in childhood: a case report and pilot study

ACTA PAEDIATRICA, Issue 7 2009
T Kallinich
Abstract Hyperthermia is characterized by an increase of body core temperature due to exogenous heat exposure and/or endogenous heat production. Contrary to fever the hypothalamic-controlled temperature set point remains unchanged. Aim: To demonstrate that exercise-induced hyperthermia is a common phenomenon in childhood. Case: We describe a 5-year-old boy, who attended our outpatient clinic with a 6-month observation period of exercise-induced hyperthermia with rectal temperatures up to 39.0°C. Characteristically temperature dropped to normal values after cessation of exercise. Method: In eight children aged 5,8, tympanic and rectal temperatures were measured before and after exercise. Results: The rectal temperature increases frequently after exercise (p < 0.001), whereas tympanic temperature did not (p = 0.2). Conclusion:, Benign hyperthermia should be considered in children with increased body temperature of unknown sources. The site of temperature measurement might be critical in the identification of this condition. [source]

IDENTIFICATION OF BLOOD PRESSURE CONTROL MECHANISMS BY POWER SPECTRAL ANALYSIS

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 4 2007
Harald M Stauss
SUMMARY 1Blood pressure and organ perfusion are controlled by a variety of cardiovascular control systems, such as the baroreceptor reflex and the renin,angiotensin system (RAS), and by local vascular mechanisms, such as shear stress-induced release of nitric oxide (NO) from the endothelium and the myogenic vascular response. Deviations in arterial blood pressure from its set point activate these mechanisms in an attempt to restore blood pressure and/or secure organ perfusion. However, the response times at which different cardiovascular mechanisms operate differ considerably (e.g. blood pressure control by the RAS is slower than blood pressure control via the baroreceptor reflex). 2Owing to these different response times, some cardiovascular control systems affect blood pressure more rapidly and others more slowly. Thus, identifying the frequency components of blood pressure variability (BPV) by power spectral analysis can potentially provide important information on individual blood pressure control mechanisms. 3Evidence is presented that the RAS, catecholamines, endothelial-derived NO and myogenic vascular function affect BPV at very low frequencies (0.02,0.2 Hz) and that low-frequency (LF) BPV (0.2,0.6 Hz) is affected by sympathetic modulation of vascular tone and endothelial-derived NO in rats. In humans, LF BPV (0.075,0.15 Hz) is affected by sympathetic modulation of vascular tone and myogenic vascular function. The impact of the RAS and endothelial-derived NO on BPV in humans requires further investigation. 4In conclusion, power spectral analysis is a powerful diagnostic tool that allows identification of pathophysiological mechanisms contributing to cardiovascular diseases, such as hypertension, heart failure and stroke, because it can separate slow from fast cardiovascular control mechanisms. The limitation that some cardiovascular control mechanisms affect the same frequency components of BPV requires the combination of blood pressure spectral analysis with other techniques. [source]

Normative data of bone mineral density in an unselected adult Austrian population

EUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 4 2003
S. Kudlacek
Abstract Background There is increasing evidence that correct interpretation of bone mineral density (BMD) measurements by dual energy X-ray absorptiometry (DEXA) requires a population-specific reference range. We therefore collected data on age-related BMD in a random sample of the normal adult Austrian population to establish an appropriate normative database. Methods We measured BMD by DEXA at five different skeletal sites in 1089 subjects, i.e. 654 females and 435 males, aged between 21,76 years, who had been recruited by 17 centres across Austria. Results Age-related bone loss was observed until age 65 years with significant changes at the lumbar spine (r = ,0·23), total hip (r = ,0·07), trochanter (r = ,0·10), femoral neck (r = ,0·30) and Ward's triangle (r = ,0·40) in the women but only at the femoral neck (r = ,0·23) and at Ward's triangle (r = ,0·40) in the men. When we calculated T scores from the BMD data of the young normal adult study population and used the T score set points according to the WHO classification of osteopenia and osteoporosis, we found that, depending on the skeletal site measured, 7·6,27·4% of the women and 16,41% of the men in our study group had low bone mass, whereas 0·6,2·7% of the female and 0·2,1·0% of the male study population were osteoporotic. However, osteoporosis was indicated in 4,9-fold more females and 5,15-fold more males when we based our estimates on the normative data provided by the manufacturers of the DEXA systems. Conclusion Our data underscore the importance of using a population-specific reference range for DEXA measurements to avoid overdiagnosis of osteoporosis. [source]

Extended antiretroviral treatment interruption in HIV-infected patients with long-term suppression of plasma HIV RNA

HIV MEDICINE, Issue 1 2005
CJ Achenbach
Objectives Evaluation of extended treatment interruption (TI) in chronic HIV infection among patients successfully treated with antiretroviral therapy. Methods An observational analysis of 25 patients in a prospectively followed cohort with chronic HIV infection, viral loads <500 HIV-1 RNA copies/mL for at least 6 months, and an interruption in therapy of ,28 days duration was carried out. Follow up was divided into 3-month time periods for analysis. The effects of time period, stratification group and stratification group by time period interactions on CD4 counts were tested using a mixed model. Univariate comparisons among patient characteristics and responses were performed using Fisher's exact test or the Wilcoxon rank sum test. Results At initiation of TI, the median CD4 count was 799 cells/,L. TI duration was a median of 7.1 months. HIV RNA rebounded to a median maximum level of 75 000 copies/mL. Maximum viral rebound was significantly greater in patients who were male, had lipodystrophy and had zenith HIV RNA prior to TI of ,50 000 copies/mL. Lower CD4 cell counts were observed during TI in patients with lipodystrophy, zenith HIV RNA ,50 000 copies/mL, history of AIDS, HIV infection ,5 years and presuppression CD4 count ,350 cells/,L. Patients who reinitiated therapy had shorter TI duration, presuppression CD4 count ,350 cells/,L, previous AIDS diagnosis and lipodystrophy. No patients developed adverse or AIDS-defining events during TI. Conclusions Long-term TI resulted in greater immune deterioration in patients with high viral set points or low CD4 cell counts prior to initiation of suppressive antiretroviral therapy. [source]

A cost-effective operating strategy to reduce energy consumption in a HVAC system

COMPUTER-CONTROLLED MICROWAVE HEATING TO IN-PACKAGE PASTEURIZE BEEF FRANKFURTERS FOR ELIMINATION OF LISTERIA MONOCYTOGENES,

JOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2005
LIHAN HUANG
ABSTRACT The objective of this study was to develop an in-package pasteurization technology to kill Listeria monocytogenes in ready-to-eat meats using microwave heating. This technology utilized an infrared sensor to monitor the surface temperature of beef frankfurters during microwave heating. The aim was to increase the surface temperature of frankfurters to a set point lethal to L. monocytogenes. A feedback control mechanism was used to control the power to the microwave oven. Results indicated that the simple on-off control mechanism was able to maintain the surface temperature of beef frankfurters near the respective set points of 75, 80 or 85C used in this study. This pasteurization process was able to achieve a 7-log reduction of L. monocytogenes in inoculated beef frankfurters using a 600-W nominally rated microwave oven within 12,15 min. If optimized, this system may provide the food industry with a terminal, postlethality pasteurization technology to kill L. monocytogenes in ready-to-eat meats within the final packages. [source]

A Short Note About Energy-Efficiency Performance of Thermally Coupled Distillation Sequences

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2006
Juan Gabriel Segovia-Hernández
Abstract In this work, we present a comparative study of the energy-efficiency performance between conventional distillation sequences and thermally coupled distillation arrangements (TCDS) for the separation of ternary mixtures of hydrocarbons under the action of feedback control loops. The influence of the relative ease of separation of the feed mixture and its composition was analyzed. The feedback analysis was conducted through servo tests with individual changes in the set points for each of the three product streams. Standard PI controllers were used for each loop. The results show an apparent trend regarding the sequence with a better dynamic performance. Generally, TCDS options performed better for the control of the extreme components of the ternary mixture (A and C), while the conventional sequences offered a better dynamic behaviour for the control of the intermediate component (B). The only case in which there was a dominant structure for all control loops was when the feed contained low amounts of the intermediate component and the mixture had similar relative volatilities. The Petlyuk column provided the optimal choice in such case, which contradicts the general expectations regarding its control behaviour. In addition, the energy demands during the dynamic responses were significantly lower than those observed for the other distillation sequences. TCDS options, therefore, are not only more energy efficient than the conventional sequences, but there are cases in which they also offer better feedback control properties. On présente dans ce travail une étude comparative de la performance d'efficacité d'énergétique entre les séquences de distillation conventionnelles et les configurations de distillation couplées thermiquement (TCDS) pour la séparation de mélanges ternaires d'hydrocarbures sous l'action de boucles de contrôle d'asservissement. L'influence de la facilité relative de séparation du mélange d'alimentation et de sa composition est analysée. L'analyse de rétroalimentation est réalisée grâce à des tests d'asservissement avec des changements individuels dans les points de consigne pour chacun des trois courants de produits. Des contrôleurs PI standards ont été utilisés pour chaque boucle. Les résultats montrent une tendance apparente pour la séquence ayant une meilleure performance dynamique. Généralement, les options TCDS sont meilleures pour le contrôle des composantes extrêmes du mélange ternaire (A et C), tandis que les séquences conventionnelles offrent un meilleur contrôle dynamique pour le contrôle de la composante intermédiaire (B). Le seul cas où il y a une structure dominante pour toutes les boucles de contrôle, c'est lorsque l'alimentation contenant de faibles quantités de la composante intermédiaire et le mélange ont la même volatilité relative. La colonne Petlyuk est le choix optimal dans un tel cas, ce qui contredit les attentes générales concernant son comportement de contrôle. En outre, les demandes d'énergie pendant les réponses dynamiques sont significativement plus faibles que celles observées pour les autres séquences de distillation. Ainsi, non seulement les options TCDS sont plus efficaces que les séquences conventionnelles, mais il y a des cas où elles offrent également de meilleures propriétés de contrôle d'asservissement. [source]

Optimization of fed-batch parameters and harvest time of CHO cell cultures for a glycosylated product with multiple mechanisms of inactivation

BIOTECHNOLOGY & BIOENGINEERING, Issue 2 2007
Ryan S. Senger
Abstract Optimization of fed-batch feeding parameters was explored for a system with multiple mechanisms of product inactivation. In particular, two separate mechanisms of inactivation were identified for the recombinant tissue-type activator (r-tPA) protein. Dynamic inactivation models were written to describe particular r-tPA glycoform inactivation in the presence and absence of free-glucose. A glucose-independent inactivation mechanism was identified, and inactivation rate constants were found dependent upon the presence of glycosylation of r-tPA at N184. Inactivation rate constants of the glucose-dependent mechanism were not affected by glycosylation at N184. Fed-batch optimization was performed for r-tPA production by CHO cell culture in a stirred-tank reactor with glucose, glutamine and asparagine feed. Feeding profiles in which culture supernatant concentrations of free-glucose and amino acids (combined glutamine and asparagine) were used as control variables, were evaluated for a wide variety of set points. Simulation results for a controlled feeding strategy yielded an optimum at set points of 1.51 g L,1 glucose and 1.18 g L,1 of amino acids. Optimization was also performed in absence of metabolite control using fixed feed-flow rates initiate during the exponential growth phase. Fixed feed-flow results displayed a family of optimum solutions along a mass flow rate ratio of 3.15 of glucose to amino acids. Comparison of the two feeding strategies showed a slight advantage of rapid feeding at a fixed flow rate as opposed to metabolite control for a product with multiple mechanisms of inactivation. Biotechnol. Bioeng. 2007;98: 378,390. © 2007 Wiley Periodicals, Inc. [source]

Production of indole diterpenes by Aspergillus alliaceus

BIOTECHNOLOGY & BIOENGINEERING, Issue 5 2006
B. Junker
Abstract Production of two related indole diterpenes (differing by a dimethyl leucine side chain) by Aspergillus alliaceus was improved through several pilot scale fermentations. Media were optimized through focus primarily on initial increases, as well as mid-cycle additions, of carbon and nitrogen sources. Fermentation conditions were improved by varying ventilation conditions using various combinations of air flowrate and back-pressure set points. Production improvements were quantified based on total indole diterpene concentration as well as the ratio of the major-to-minor by-product components. Those changes with a positive substantial impact primarily on total indole diterpene concentration included early cycle glycerol shots and enhanced ventilation conditions (high air flowrate, low back-pressure). Those changes with a significant impact primarily on ratio included higher initial cerelose, soybean oil, monosodium glutamate, tryptophan, or ammonium sulfate concentrations, higher broth pH, and enhanced ventilation conditions. A few changes (higher initial glycerol and monosodium glutamate concentrations) resulted in less notable and desirable titer or ratio changes when implemented individually, but they were adopted to more fully realize the impact of other improvements or to simplify processing. Overall, total indole diterpene titers were improved at the 600 L pilot scale from 125,175 mg/L with a ratio of about 2.1 to 200,260 mg/L with a ratio of about 3.3,4.5. Thus, the ability to optimize total indole diterpene titer and/or ratio readily exists for secondary metabolite production using Aspergillus cultures. © 2006 Wiley Periodicals, Inc. [source]