5,961 research outputs found
A Streamwise Constant Model of Turbulence in Plane Couette Flow
Streamwise and quasi-streamwise elongated structures have been shown to play
a significant role in turbulent shear flows. We model the mean behavior of
fully turbulent plane Couette flow using a streamwise constant projection of
the Navier Stokes equations. This results in a two-dimensional, three velocity
component () model. We first use a steady state version of the model to
demonstrate that its nonlinear coupling provides the mathematical mechanism
that shapes the turbulent velocity profile. Simulations of the model
under small amplitude Gaussian forcing of the cross-stream components are
compared to DNS data. The results indicate that a streamwise constant
projection of the Navier Stokes equations captures salient features of fully
turbulent plane Couette flow at low Reynolds numbers. A system theoretic
approach is used to demonstrate the presence of large input-output
amplification through the forced model. It is this amplification
coupled with the appropriate nonlinearity that enables the model to
generate turbulent behaviour under the small amplitude forcing employed in this
study.Comment: Journal of Fluid Mechanics 2010, in pres
Robust control in presence of parametric uncertainties: Observer-based feedback controller design
Feedback regulation of the heat shock response in E. coli
Survival of organisms in extreme conditions has necessitated the evolution of stress response networks that detect and respond to environmental changes. Among the extreme conditions that cells must face is the exposure to higher than normal temperatures. In this paper, we propose a detailed biochemical model that captures the dynamical nature of the heat-shock response in Escherichia coli. Using this model, we show that both feedback and feedforward control are utilized to achieve robustness, performance, and efficiency of the response to the heat stress. We discuss the evolutionary advantages that feedback confers to the system, as compared to other strategies that could have been implemented to get the same performance
Total synthesis of the post-translationally modified polyazole peptide antibiotic goadsporin
The structurally unique polyazole antibiotic goadsporin contains six heteroaromatic oxazole and thiazole rings integrated into a linear array of amino acids that also contains two dehydroalanine residues. An efficient total synthesis of goadsporin is reported in which the key steps are the use of rhodium(II)-catalyzed reactions of diazocarbonyl compounds to generate the four oxazole rings, which demonstrates the power of rhodium carbene chemistry in organic chemical synthesis
Motifs, Control, and Stability
The interactions of networks of transcription factors and signaling molecules can be understood, in part, through concepts from control theory and engineering
The contribution of health risk behaviors to excess mortality in American adults with chronic hepatitis C: a population cohort-study
Natural recovery of genetic diversity by gene flow in reforested areas of the endemic Canary Island pine, Pinus canariensis
The endemic pine, Pinus canariensis, forms one of the main forest ecosystems
in the Canary Islands. In this archipelago, pine forest is a mosaic of natural
stands (remnants of past forest overexploitation) and artificial stands planted
from the 1940's. The genetic makeup of the artificially regenerated forest is
of some concern. The use of reproductive material with uncontrolled origin or
from a reduced number of parental trees may produce stands ill adapted to local
conditions or unable to adapt in response to environmental change. The genetic
diversity within a transect of reforested stands connecting two natural forest
fragments has been studied with nuclear and chloroplast microsatellites. Little
genetic differentiation and similar levels of genetic diversity to the
surrounding natural stands were found for nuclear markers. However, chloroplast
microsatellites presented lower haplotype diversity in reforested stands, and
this may be a consequence of the lower effective population size of the
chloroplast genome, meaning chloroplast markers have a higher sensitivity to
bottlenecks. Understory natural regeneration within the reforestation was also
analysed to study gene flow from natural forest into artificial stands.
Estimates of immigration rate into artificially regenerated forest were high
(0.68-0.75), producing a significant increase of genetic diversity (both in
chloroplast and nuclear microsatellites), which indicates the capacity for
genetic recovery for P. canariensis reforestations surrounded by larger natural
stands
Undergraduate Course in Environmental Design and Manufacturing
This paper is a progress report on the development of an undergraduate course in environmental design and manufacturing. The importance of the topic is clear from National Academy of Engineering statements regarding the need to incorporate content on sustainable technology. The multidisciplinary team includes academic faculty from engineering, science, liberal studies, and business in collaboration with industry partners. The team\u27s approach is to create a case-based course by adapting existing educational modules from Ford Motor Company. The group has received National Science Foundation funding for this project (DUE-0511322), and the project is currently in its beginning phases
Agitation near the end of life with dementia: An ethnographic study of care
Background and objectives
Agitation is common in people living with dementia especially at the end of life. We examined how staff interpreted agitation behavior in people with dementia nearing end of life, how this may influence their responses and its impact on the quality of care.
Research design
Ethnographic study. Structured and semi-structured non-participant observations (referred to subsequently in this paper as “structured observations”) of people living with dementia nearing the end of life in hospital and care homes (south-east England) and in-depth interviews with staff, conducted August 2015-March 2017.
Methods
Three data sources: 1) detailed field notes, 2) observations using a structured tool and checklist for behaviors classed as agitation and staff and institutional responses, 3) staff semi-structured qualitative interviews. We calculated the time participants were agitated and described staff responses. Data sources were analyzed separately, developed continuously and relationally during the study and synthesized where appropriate.
Results
We identified two main ‘ideal types’ of staff explanatory models for agitation: In the first, staff attribute agitated behaviors to the person’s “moral judgement”, making them prone to rejecting or punitive responses. In the second staff adopt a more “needs-based” approach in which agitation behaviors are regarded as meaningful and managed with proactive and investigative approaches. These different approaches appear to have significant consequences for the timing, frequency and quality of staff response. While these models may overlap they tend to reflect distinct organizational resources and values.
Conclusions
Care worker knowledge about agitation is not enough, and staff need organizational support to care better for people living with dementia towards end of life. Positional theory may help to explain much of the cultural-structural context that produces staff disengagement from people with dementia, offering insights on how agitation behavior is reframed by some staff as dangerous. Such behavior may be associated with low-resource institutions with minimal staff training where the personhood of staff may be neglected
- …