Home About us Contact
|
Home About us Contact | ||
|
|
||
Changing Conditions (changing + condition)
Selected AbstractsMarine diatom species harbour distinct bacterial communitiesENVIRONMENTAL MICROBIOLOGY, Issue 6 2005Hans-Peter Grossart Summary We examined bacterial dynamics in batch cultures of two axenic marine diatoms (Thalassiosira rotula and Skeletonema costatum). The axenic diatoms were inoculated with natural bacterial assemblages and monitored by 4,6-diamidino-2-phenolindole (DAPI) counts, denaturing gradient gel electrophoresis (DGGE) with subsequent analysis of excised, sequenced 16S rRNA gene fragments, and fluorescence in situ hybridization (FISH) with group-specific 16S rRNA oligonucleotide probes. Our results show that algal growth exhibited pronounced differences in axenic treatments and when bacteria were present. Bacterial abundance and community structure greatly depended on species, growth and physiological status of even closely related algae. Free-living and phytoplankton-associated bacteria were very different from each other and were dominated by distinct phylogenetic groups. The diatom-associated bacteria mainly belonged to the Flavobacteria,Sphingobacteria group of the Bacteroidetes phylum whereas free-living bacteria, which were rather similar in both cultures, comprised mainly of members of the Roseobacter,group ,of ,,- Proteobacteria. ,Presence and disappearance of specific bacteria during algal growth indicated pronounced differences in environmental conditions over time and selection of bacteria highly adapted to the changing conditions. Tight interactions between marine bacteria and diatoms appear to be important for the decomposition of organic matter and nutrient cycling in the sea. [source] Processing, modelling and predicting time-lapse effects of overpressured fluid-injection in a fractured reservoirGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2002Erika Angerer Summary Time-lapse seismology is important for monitoring subsurface pressure changes and fluid movements in producing hydrocarbon reservoirs. We analyse two 4-D, 3C onshore surveys from Vacuum Field, New Mexico, USA, where the reservoir of interest is a fractured dolomite. In Phase VI, a time-lapse survey was acquired before and after a pilot tertiary-recovery programme of overpressured CO2 injection, which altered the fluid composition and the pore-fluid pressure. Phase VII was a similar time-lapse survey in the same location but with a different lower-pressure injection regime. Applying a processing sequence to the Phase VI data preserving normal-incidence shear-wave anisotropy (time-delays and polarization) and maximizing repeatability, interval-time analysis of the reservoir interval shows a significant 10 per cent change in shear-wave velocity anisotropy and 3 per cent decrease in the P -wave interval velocities. A 1-D model incorporating both saturation and pressure changes is matched to the data. The saturation changes have little effect on the seismic velocities. There are two main causes of the time-lapse changes. Any change in pore-fluid pressures modifies crack aspect ratios. Additionally, when there are overpressures, as there are in Phase VI, there is a 90° change in maximum impedance directions, and the leading faster split shear wave, instead of being parallel to the crack face as it is for low pore-fluid pressures, becomes orthogonal to the crack face. The anisotropic poro-elasticity (APE) model of the evolution of microcracked rock, calculates the evolution of cracked rock to changing conditions. APE modelling shows that at high overburden pressures only nearly vertical cracks, to which normal incidence P waves are less sensitive than S waves, remain open as the pore-fluid pressure increases. APE modelling matches the observed time-lapse effects almost exactly demonstrating that shear-wave anisotropy is a highly sensitive diagnostic of pore-fluid pressure changes in fractured reservoirs. In this comparatively limited analysis, APE modelling of fluid-injection at known pressure correctly predicted the changes in seismic response, particularly the shear-wave splitting, induced by the high-pressure CO2 injection. In the Phase VII survey, APE modelling also successfully predicted the response to the lower-pressure injection using the same Phase VI model of the cracked reservoir. The underlying reason for this remarkable predictability of fluid-saturated reservoir rocks is the critical nature and high crack density of the fluid-saturated cracks and microcracks in the reservoir rock, which makes cracked reservoirs critical systems. [source] The joint effects of larval density and 14C-cypermethrin on the life history and population growth rate of the midge Chironomus ripariusJOURNAL OF APPLIED ECOLOGY, Issue 6 2003Helen L. Hooper Summary 1Chemical effects on organisms are typically assessed using individual-level endpoints or sometimes population growth rate (PGR), but such measurements are generally made at low population densities. In contrast most natural populations are subject to density dependence and fluctuate around the environmental carrying capacity as a result of individual competition for resources. As ecotoxicology aims to make reliable population projections of chemical impacts in the field, an understanding of how high-density or resource-limited populations respond to environmental chemicals is essential. 2Our objective was to determine the joint effects of population density and chemical stress on the life history and PGR of an important ecotoxicological indicator species, Chironomus riparius, under controlled laboratory conditions. Populations were fed the same ration but initiated at different densities and exposed to a solvent control and three concentrations of 14C-cypermethrin in a sediment,water test system for 67 days at 20 ± 1 °C. 3Density had a negative effect on all the measured life-history traits, and PGR declined with increasing density in the controls. Exposure to 14C-cypermethrin had a direct negative effect on juvenile survival, presumably within the first 24 h because the chemical rapidly dissipated from the water column. Reductions in the initial larval densities resulted in an increase in the available resources for the survivors. Subsequently, exposed populations emerged sooner and started producing offspring earlier than the controls. 14C-cypermethrin had no effect on estimated fecundity and adult body weight but interacted with density to reduce the time to first emergence and first reproduction. As a result, PGR increased with cypermethrin concentration when populations were initiated at high densities. 4Synthesis and applications. The results showed that the effects of 14C-cypermethrin were buffered at high density, so that the joint effects of density and chemical stress on PGR were less than additive. Low levels of chemical stressors may increase carrying capacity by reducing juvenile competition for resources. More and perhaps fitter adults may be produced, similar to the effects of predators and culling; however, toxicant exposure may result in survivors that are less tolerant to changing conditions. If less than additive effects are typical in the field, standard regulatory tests carried out at low density may overestimate the effects of environmental chemicals. Further studies over a wide range of chemical stressors and organisms with contrasting life histories are needed to make general recommendations. [source] Autonomy through identification: a qualitative study of the process of identification used by people with type 2 diabetesJOURNAL OF CLINICAL NURSING, Issue 7b 2008Albine Moser MPH Aims and objectives., The aim of this study is to clarify the process of identification with diabetes as a dimension of autonomy as described by people with type 2 diabetes. Background., People with type 2 diabetes view autonomy as competency in shaping one's life. This concept of autonomy has seven dimensions, which emerged as categories in prior research. Dynamic processes shape these dimensions of autonomy. One of the dimensions of autonomy is identification. Method., This study has a qualitative descriptive and exploratory design and an inductive approach as described in grounded theory. Data were collected by means of in-depth interviews. The sample consisted of 15 people with type 2 diabetes mellitus in a nurse-led, shared-care setting in the Netherlands. Results., The phases of identification are comprehending, struggling, evaluating and mastering. Each phase has its own characteristics. Identifying with the diabetes is a non-linear, cyclical and continuous process because people with diabetes have to deal with changing conditions. Conclusion., The dynamics of identification is directed to a process of identifying with diabetes and its care requirement. Recognizing identification as an element of autonomy enables nurses to adopt a more patient-oriented view of autonomy. Relevance to clinical practice., Nursing that fosters the process of identification promotes autonomy. This implies that a person with diabetes should be able to identify with the nurse's interventions. Hence it is vital that nurses build supportive partnerships when providing care for such a patient. [source] Regulatory reform and managerial choice: an analysis of the cost savings from airline deregulationMANAGERIAL AND DECISION ECONOMICS, Issue 2-3 2008Margaret Peteraf This paper explores the question of how the differential exercise of managerial choice can facilitate organizational adaptation and improve efficiency over periods of regulatory change. We address this question in the context of the US airline industry, with a detailed decomposition of an airline cost function. Our findings suggest that managers employ choice in unconstrained domains to counteract the effects of constrained or pre-determined choices. This is an adaptive mechanism that helps firms adjust to environmental change or maneuver over a rugged landscape. We view this as a type of dynamic managerial capability for achieving dynamic fit under changing conditions. Copyright © 2008 John Wiley & Sons, Ltd. [source] High gene flow promotes the genetic homogeneity of the fish goby Pomatoschistus marmoratus (Risso, 1810) from Mar Menor coastal lagoon and adjacent marine waters (Spain)MARINE ECOLOGY, Issue 2 2010Carlos Vergara-Chen Abstract The extreme environmental variability of coastal lagoons suggests that physical and ecological factors could contribute to the genetic divergence among populations occurring in lagoon and open-coast environments. In this study we analysed the genetic variability of lagoon and marine samples of the sand goby, Pomatoschistus marmoratus (Risso, 1810) (Pisces: Gobiidae), on the SW Spain coast. A fragment of mitochondrial DNA control region (570 bp) was sequenced for 196 individuals collected in five localities: Lo Pagan, Los Urrutias and Playa Honda (Mar Menor coastal lagoon), and Veneziola and Mazarrón (Mediterranean Sea). The total haplotype diversity was h = 0.9424 ± 0.0229, and the total nucleotide diversity was , = 0.0108 ± 0.0058. Among-sample genetic differentiation was not significant and small-scale patterns in the distribution of haplotypes were not apparent. Gene flow and dispersal-related life history traits may account for low genetic structure at a small spatial scale. The high genetic diversity found in P. marmoratus increases its potential to adapt to changing conditions of the Mar Menor coastal lagoon. [source] The ecology and evolutionary endocrinology of reproduction in the human femaleAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue S49 2009Virginia J. Vitzthum Abstract Human reproductive ecology (HRE) is the study of the mechanisms that link variation in reproductive traits with variation in local habitats. Empirical and theoretical contributions from biological anthropology, physiology, and demography have established the foundation necessary for developing a comprehensive understanding, grounded in life history theory (LHT), of temporal, individual, and populational variation in women's reproductive functioning. LHT posits that natural selection leads to the evolution of mechanisms that tend to allocate resources to the competing demands of growth, reproduction, and survival such that fitness is locally maximized. (That is, among alternative allocation patterns exhibited in a population, those having the highest inclusive fitness will become more common over generational time.) Hence, strategic modulation of reproductive effort is potentially adaptive because investment in a new conception may risk one's own survival, future reproductive opportunities, and/or current offspring survival. The hypothalamic-pituitary-ovarian (HPO) axis is the principal neuroendocrine pathway by which the human female modulates reproductive functioning according to the changing conditions in her habitat. Adjustments of reproductive investment in a potential conception are manifested in temporal and individual variation in ovarian cycle length, ovulation, hormone levels, and the probability of conception. Understanding the extent and causes of adaptive and non-adaptive variation in ovarian functioning is fundamental to ascertaining the proximate and remote determinants of human reproductive patterns. In this review I consider what is known and what still needs to be learned of the ecology of women's reproductive biology, beginning with a discussion of the principal explanatory frameworks in HRE and the biometry of ovarian functioning. Turning next to empirical studies, it is evident that marked variation between cycles, women, and populations is the norm rather than an aberration. Other than woman's age, the determinants of these differences are not well characterized, although developmental conditions, dietary practices, genetic variation, and epigenetic mechanisms have all been hypothesized to play some role. It is also evident that the reproductive functioning of women born and living in arduous conditions is not analogous to that of athletes, dieters, or even the lower end of the "normal range" of HPO functioning in wealthier populations. Contrary to the presumption that humans have low fecundity and an inefficient reproductive system, both theory and present evidence suggest that we may actually have very high fecundity and a reproductive system that has evolved to be flexible, ruthlessly efficient and, most importantly, strategic. Yrbk Phys Anthropol 52:95,136, 2009. © 2009 Wiley-Liss, Inc. [source] Farming flexibility and food security under climatic uncertainty: Manang, Nepal HimalayaAREA, Issue 2 2010Tor Halfdan Aase Climate change is predicted to cause a substantial decrease in food production in poor regions during this century. But since reliable models of future climates have not been produced at local level as yet, this article focuses on the flexibility of farming systems in terms of adaptability to changing conditions of production, whatever those changes may turn out to be. Defining flexibility as ,uncommitted potentiality for change'Bateson 1972, the aim of the article is to identify such potentialities among subsistence farmers in a remote part of the Himalayas. Our analysis reveals four ,uncommitted potentialities' for adaptation to a future situation that will be climatologically different from the present. In order to maintain local food security under changing climate conditions, farmers in the study valley of Manang can reclaim abandoned land, they can depend more on barley, they may reduce the conspicuous exhibition of horses, and relocate farming from the slope to the valley bottom. The inherent flexibility in their farming system renders Mananges quite robust in facing future uncertainties. Thus, Manang is more appropriately labelled ,dynamic' than ,fragile', which is a term often ascribed to high Himalayan communities and environments. [source] Re-imagining Relevance: A Response to Starkey and MadanBRITISH JOURNAL OF MANAGEMENT, Issue 2001Christopher Grey Starkey and Madan (2001) propose that changing conditions of knowledge production mean that business schools face an increasing relevance gap which, if they do not respond, will be filled by management consultants and corporate universities. In this response, I question the core assumptions of their analysis, suggesting that they misunderstand both the historical role and present practices of universities and business schools. In particular they fail to understand the complexities of knowledge production, its relationship to practice and the importance of ,independence' which is the unique contribution that universities make to society. I argue that their proposal to bridge the relevance gap would, if adopted, have the effect of leaving business schools with no defensible social role. Thus, ironically, their ,solution' to the challenges facing business schools would in fact exacerbate the problems they currently face. [source] Modeling of Particle Layer Detachment under Consideration of Transient Kinetic EffectsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2010Q. Zhang Abstract Particle layers tend to build up on walls in many filtration and separation processes, calling for periodic removal in order to keep the device running. Important factors are the adhesion of the layer on the substrate and the cohesion of the particles in the layer. Models describing such layer detachment generally assume constant and homogeneous conditions for the forces acting on the layer. But in reality detachment is extremely nonstationary concerning place and time, primarily due to changing conditions for the forces on the one hand and changes in the particle layer morphology on the other. This paper describes a model and a simulation considering such transient kinetic effects on filter cake detachment. Diverse computing results are presented and discussed. [source] | |||||||||||||