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Limiting Conditions (limiting + condition)

Distribution by Scientific Domains

Life Sciences	33%

Selected Abstracts

Liquid Chromatography of Synthetic Polymers under Limiting Conditions of Insolubility III

MACROMOLECULAR SYMPOSIA, Issue 1 2007
Application of Monolithic Columns
Abstract Summary Performance was evaluated of silica based commercial monolithic rod-like columns in liquid chromatography of synthetic polymers under limiting conditions of enthalpic interactions (LC LC). LC LC employs the barrier effect of the pore permeating and therefore slowly eluting small molecules toward the pore excluded, fast eluting macromolecules. Phase separation (precipitation) barrier action was applied in present study. The barrier was created either by the narrow pulse of an appropriate nonsolvent injected into the column just before the sample solution (LC LC of insolubility , LC LCI) or by the eluent itself. In the latter case, the polymer sample was dissolved and injected in a good solvent (LC LC of solubility , LC LCS). In LC LCI, polymer species cannot break thru the nonsolvent zone while in LC LCS they cannot enter eluent, which is their precipitant. Therefore, polymer species keep moving in the zone of their original solvent. Macromolecules eluting under the LC LC mechanism leave the column in the retention volume (VR) roughly corresponding to VR of the low molar mass substances and can be efficiently separated from the polymer species non-hindered by the barrier action. The known advantages of monoliths were confirmed. From the point of view of LC LCI and LC LCS the most important quality of monolithic columns represents their excellent permeability, which allows both working at high flow rates and injecting very high (in the range of 5%) sample concentrations. Monolithic column tolerate also extremely high molar mass samples (M>10,000 kg,·,mol,1). On the other hand, the mesopores (separation pores) of the tested monoliths exhibited rather small volume and wide size distribution. These shortcomings partially impair the permeability advantage of monoliths because in order to obtain high LC LC separation selectivity a tandem of several monolithic columns must be applied. Presence of large mesopores also reduces applicability of monolithic columns for molar masses below about 50 kg,·,mol,1 because VRs of polymers eluted behind the barrier are similar to that of freely eluting species. The non- negligible break-thru phenomenon was observed for the very high polymer molar masses largely eluting behind the barrier. It is assumed that the fraction of very large mesopores present in the monoliths or association/microphase separation of macromolecules may be responsible for this phenomenon. This is why the presently marketed SiO2 monolithic columns are mainly suitable for the fast purification of the LC LC eluting macromolecules from the polymeric admixtures non-hindered by the barrier-forming liquid. Still, monolithic columns have large potential in the LC LCI and LC LCS procedures provided size (effective diameter) of the mesopores can be reduced and their volume increased. [source]

Time to precept: supportive and limiting conditions for precepting nurses.

JOURNAL OF ADVANCED NURSING, Issue 2 2010
Elisabeth Carlson
carlson e., pilhammar e. & wann-hansson c. (2010) Time to precept: supportive and limiting conditions for precepting nurses. Journal of Advanced Nursing66(2), 432,441. Abstract Title.,Time to precept: supportive and limiting conditions for precepting nurses. Aim., This paper is a report of a study describing conditions for precepting in a Swedish clinical context from the perspective of precepting nurses. Background., Clinical practice is a complex part of nursing education, and registered nurses who are acting as preceptors for nursing students face a number of challenges that need to be addressed during the precepting process. Method., An ethnographic approach guided by symbolic interactionism was used. Data were collected by participant observation and focus group interviews over a ten-month period in 2006,2007. Participants were selected by purposive sampling of 13 staff nurses who were preceptors during the field work period. In addition, 16 staff nurses, experienced in precepting, were purposively selected for four focus groups. Findings., Precepting was found to be a complex function for nurses, influenced by conditions that could be both supportive and limiting in nature. Three themes described these conditions: organization, comprising clinical responsibilities and routines; collaboration, focusing on professional relations and interactions; and the personal perspective, comprising preceptors' experiences, need for feed back and notions of benefits. Time as a limiting condition reappeared through all categories. Conclusion., It is important to raise the issue of time and its impact on the precepting process. Precepting needs to be further discussed in terms of an integrated nursing competence prioritized by all stakeholders involved in clinical practice. Therefore; efforts should be made to plan nurses' clinical work so that allocated time for precepting can be facilitated. [source]

Lack of main K+ uptake systems in Saccharomyces cerevisiae cells affects yeast performance in both potassium-sufficient and potassium-limiting conditions

FEMS YEAST RESEARCH, Issue 5 2010
Clara Navarrete
Abstract A new YNB medium containing very low concentrations of alkali metal cations has been developed to carry out experiments to study potassium homoeostasis. Physiological characterization of Saccharomyces cerevisiae BY4741 strain and the corresponding mutant lacking the main potassium uptake systems (trk1 trk2) under potassium nonlimiting and limiting concentrations was performed, and novel important differences between both strains were found. At nonlimiting concentrations of KCl, the two strains had a comparable cell size and potassium content. Nevertheless, mutants were hyperpolarized, had lower pH and extruded fewer protons compared with the BY4741 strain. Upon transfer to K+ -limiting conditions, cells of both strains became hyperpolarized and their cell volume and K+ content diminished; however, the decrease was more relevant in BY4741. In low potassium, trk1 trk2 cells were not able to accomplish the cell cycle to the same extent as in BY4741. Moreover, K+ limitation triggered a high-affinity K+/Rb+ uptake process only in BY4741, with the highest affinity being reached as soon as 30 min after transfer to potassium-limiting conditions. By establishing basic cellular parameters under standard growth conditions, this work aims to establish a basis for the investigation of potassium homoeostasis at the system level. [source]

Time to precept: supportive and limiting conditions for precepting nurses.

Departures from Everyday Resistance and Flexible Strategies of Domination: The Making and Unmaking of a Poor Peasant Mobilization in Bangladesh

JOURNAL OF AGRARIAN CHANGE, Issue 2 2007
SHAPAN ADNAN
James Scott's influential work has popularized the notion that everyday resistance among the peasantry takes covert and backstage forms, termed ,weapons of the weak'. This paper, however, provides a case study involving transformation of covert resistance and outward compliance of the poor into open dissent and confrontation with power-holders, though falling well short of the limiting conditions of rebellion or revolution. Such instances serve to dispel the notion that poor and weak groups adopt only covert forms of resistance in their everyday existence. The paper takes up the questions of why, and under what circumstances, such transformation of covert resistance into overt forms can come about. These issues are explored using evidence from a poor peasant mobilization in rural Bangladesh during the parliamentary election of 1986. The analysis shows that there were sequential shifts in the respective strategies of domination and resistance of the rich and the poor, which shaped each other interactively over a dynamic trajectory. Such adaptive and variable responses require an approach that can accommodate flexibility and substitution in the strategies adopted by the weak and the powerful. These also call for further exploration and analysis of the middle ground between everyday and exceptional forms of resistance. [source]

Towards a System-Oriented Framework for Analysing and Evaluating Emergency Response

JOURNAL OF CONTINGENCIES AND CRISIS MANAGEMENT, Issue 1 2010
Marcus Abrahamsson
Information can be provided by studying and evaluating past emergencies and the response in connection to them. This information would then be useful in efforts directed at preventing, mitigating and/or preparing for future emergencies. However, the analysis and evaluation of emergency response operations is not an easy task, especially when the operation involves several cooperating actors (e.g. the fire and rescue services, the police, the emergency medical services, etc.). Here, we identify and discuss four aspects of this challenge: (1) issues related to the values governing the evaluation, (2) issues related to the complexity of the systems involved, (3) issues related to the validity of the information on which the analysis and evaluation is based and (4) issues related to the limiting conditions under which the emergency response system operated. An outline of a framework for such an analysis and evaluation, influenced by systems theory, accident investigation theories and programme evaluation theories dealing with the above aspects, is introduced, discussed and exemplified using empirical results from a case study. We conclude that the proposed framework may provide a better understanding of how an emergency response system functioned during a specific operation, and help to identify the potential events and/or circumstances that could significantly affect the performance of the emergency response system, either negatively or positively. The insights gained from using the framework may allow the actors involved in the response operation to gain a better understanding of how the emergency response system functioned as a whole, as well as how the actors performed as individual components of the system. Furthermore, the information can also be useful for actors preparing for future emergencies. [source]

Liquid Chromatography of Synthetic Polymers under Limiting Conditions of Insolubility III

Expression of the Pho regulon negatively regulates biofilm formation by Pseudomonas aureofaciens PA147-2

MOLECULAR MICROBIOLOGY, Issue 2 2001
Russell D. Monds
We report the isolation of insertional mutations to the pstC and pstA genes of the phosphate-specific transport (pst) operon that results in loss of biofilm formation by Pseudomonas aureofaciens PA147-2. Consistent with the known roles of the Pst system in Escherichia coli and Pseudomonas aeruginosa, both P. aureofaciens pst mutants were demonstrated to have defects in inorganic phosphate (Pi) transport and repression of Pho regulon expression. Subsequently, biofilm formation by the wild type was shown to require a threshold concentration of extracellular Pi. The two-component regulatory pair PhoR/PhoB is responsible for upregulation of Pho regulon expression in response to Pi -limiting environments. By generating phoR mutants that were unable to express the Pho regulon, we were able to restore biofilm formation by P. aureofaciens in Pi -limiting conditions. This result suggests that gene(s) within the Pho regulon act to regulate biofilm formation negatively in low-Pi environments, and that phoR mutations uncouple PA147-2 from such regulatory constraints. Furthermore, the inability of pst mutants to repress Pho regulon expression accounts for their inability to form biofilms in non-limiting Pi environments. Preliminary evidence suggests that the Pst system is also required for antifungal activity by PA147-2. During phenotypic analysis of pst mutants, we also uncovered novelties in relation to Pi assimilation and Pho regulon control in P. aureofaciens. [source]

Ultraviolet-B Radiation Effects on the Structure and Function of Lower Trophic Levels of the Marine Planktonic Food Web

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2006
Gustavo A. Ferreyra
ABSTRACT The impact of UV-B radiation (UVBR; 280,320 nm) on lower levels of a natural plankton assemblage (bacteria, phytoplankton and microzooplankton) from the St. Lawrence Estuary was studied during 9 days using several immersed outdoor mesocosms. Two exposure treatments were used in triplicate mesocosms: natural UVBR (N treatment, considered as the control treatment) and lamp-enhanced UVBR (H treatment, simulating 60% depletion of the ozone layer). A phytoplankton bloom developed after day 3, but no significant differences were found between treatments during the entire experiment for phytoplankton biomass (chlorophyll a and cell carbon) nor for phytoplankton cell abundances from flow cytometry and optical microscopy of three phytoplankton size classes (picoplankton, nanoplankton and microplankton). In contrast, bacterial abundances showed significantly higher values in the H treatment, attributed to a decrease in predation pressure due to a dramatic reduction in ciliate biomass (, 70,80%) in the H treatment relative to the N treatment. The most abundant ciliate species were Strombidinium sp., Prorodon ovum and Tintinnopsis sp.; all showed significantly lower abundances under the H treatment. P. ovum was the less-affected species (50% reduction in the H treatment compared with that of the N control), contrasting with ,90% for the other ones. Total specific phytoplanktonic and bacterial production were not affected by enhanced UVBR. However, both the ratio of primary to bacterial biomass and production decreased markedly under the H treatment. In contrast, the ratio of phytoplankton to bacterial plus ciliate carbon biomass showed an opposite trend than the previous results, with higher values in the H treatment at the end of the experiment. These results are explained by the changes in the ciliate biomass and suggest that UVBR can alter the structure of the lower levels of the planktonic community by selectively affecting key species. On the other hand, linearity between particulate organic carbon (POC) and estimated planktonic carbon was lost during the postbloom period in both treatments. On the basis of previous studies, our results can be attributed to the aggregation of carbon released by cells to the water column in the form of transparent exopolymer particles (TEPs) under nutrient limiting conditions. Unexpectedly, POC during such a period was higher in the H treatment than in controls. We hypothesize a decrease in the ingestion of TEPs by ciliates, in coincidence with increased DOC release by phytoplankton cells under enhanced UVBR. The consequences of such results for the carbon cycle in the ocean are discussed. [source]

Prediction of Minimum Fluidization Velocity in Two and Three Phase Inverse Fluidized Beds

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
Thiruvengadam Renganathan
Abstract Generalized equations for predicting minimum fluidization velocities in two-phase L-S and three-phase G-L-S inverse fluidized bed are developed covering a wide range of variables using the experimental data obtained from the present work and that available in the literature. It is found that the classical Wen and Yu equation for predicting minimum fluidization velocity can satisfactorily be used for two-phase inverse fluidized bed. A model based on empiricism and another based on the gas perturbed liquid model, which reduce to limiting conditions such as liquid solid and three-phase batch liquid systems are proposed. Des équations généralisées pour la prédiction des vitesses de fluidisation minimales dans des lits fluidisés inverses biphasique liquide-solides et triphasique gaz-liquide-solides ont été établies pour une vaste gamme de variables à l'aide des données expérimentales issues du présent travail et de la littérature scientifique. On a trouvé que l'équation classique de Wen et Yu pour prédire la vitesse de fluidisation minimale peut être utilisée pour le lit fluidisé inverse biphasique. On propose un modèle empirique et un autre basé sur le modèle de liquide perturbé par le gaz, qui se réduisent aux conditions limitantes tels les systèmes liquides discontinus liquide-solides et triphasiques. [source]

Respirometric evaluation and modeling of glucose utilization by Escherichia coli under aerobic and mesophilic cultivation conditions

BIOTECHNOLOGY & BIOENGINEERING, Issue 1 2007
G. Insel
Abstract The study presents a mechanistic model for the evaluation of glucose utilization by Escherichia coli under aerobic and mesophilic growth conditions. In the first step, the experimental data was derived from batch respirometric experiments conducted at 37°C, using two different initial substrate to microorganism (S0/X0) ratios of 15.0 and 1.3 mgCOD/mgSS. Acetate generation, glycogen formation and oxygen uptake rate profile were monitored together with glucose uptake and biomass increase throughout the experiments. The oxygen uptake rate (OUR) exhibited a typical profile accounting for growth on glucose, acetate and glycogen. No acetate formation (overflow) was detected at low initial S0/X0 ratio. In the second step, the effect of culture history developed under long-term growth limiting conditions on the kinetics of glucose utilization by the same culture was evaluated in a sequencing batch reactor (SBR). The system was operated at cyclic steady state with a constant mean cell residence time of 5 days. The kinetic response of E.coli culture was followed by similar measurements within a complete cycle. Model calibration for the SBR system showed that E. coli culture regulated its growth metabolism by decreasing the maximum growth rate (lower ) together with an increase of substrate affinity (lower KS) as compared to uncontrolled growth conditions. The continuous low rate operation of SBR system induced a significant biochemical substrate storage capability as glycogen in parallel to growth, which persisted throughout the operation. The acetate overflow was observed again as an important mechanism to be accounted for in the evaluation of process kinetics. Biotechnol. Bioeng. 2007;96: 94,105. © 2006 Wiley Periodicals, Inc. [source]