555 research outputs found
Efficient Mixing at low Reynolds numbers using polymer additives
Mixing in fluids is a rapidly developing field of fluid mechanics
\cite{Sreen,Shr,War}, being an important industrial and environmental problem.
The mixing of liquids at low Reynolds numbers is usually quite weak in simple
flows, and it requires special devices to be efficient. Recently, the problem
of mixing was solved analytically for a simple case of random flow, known as
the Batchelor regime \cite{Bat,Kraich,Fal,Sig,Fouxon}. Here we demonstrate
experimentally that very viscous liquids at low Reynolds number, . Here we
show that very viscous liquids containing a small amount of high molecular
weight polymers can be mixed quite efficiently at very low Reynolds numbers,
for a simple flow in a curved channel. A polymer concentration of only 0.001%
suffices. The presence of the polymers leads to an elastic instability
\cite{LMS} and to irregular flow \cite{Ours}, with velocity spectra
corresponding to the Batchelor regime \cite{Bat,Kraich,Fal,Sig,Fouxon}. Our
detailed observations of the mixing in this regime enable us to confirm sevearl
important theoretical predictions: the probability distributions of the
concentration exhibit exponential tails \cite{Fal,Fouxon}, moments of the
distribution decay exponentially along the flow \cite{Fouxon}, and the spatial
correlation function of concentration decays logarithmically.Comment: 11 pages, 5 figure
Pulsating Strings in Lunin-Maldacena Backgrounds
We consider pulsating strings in Lunin-Maldacena backgrounds, specifically in
deformed Minkowski spacetime and deformed AdS_5xS^5. We find the relation
between the energy and the oscillation number of the pulsating string when the
deformation is small. Since the oscillation number is an adiabatic invariant it
can be used to explore the regime of highly excited string states. We then
quantize the string and look for such a sector. For the deformed Minkowski
background we find a precise match with the classical results if the
oscillation number is quantized as an even number. For the deformed AdS_5xS^5
we find a contribution which depends on the deformation parameter.Comment: 16 pages, 2 figures, typos fixe
Chemotactic response and adaptation dynamics in Escherichia coli
Adaptation of the chemotaxis sensory pathway of the bacterium Escherichia
coli is integral for detecting chemicals over a wide range of background
concentrations, ultimately allowing cells to swim towards sources of attractant
and away from repellents. Its biochemical mechanism based on methylation and
demethylation of chemoreceptors has long been known. Despite the importance of
adaptation for cell memory and behavior, the dynamics of adaptation are
difficult to reconcile with current models of precise adaptation. Here, we
follow time courses of signaling in response to concentration step changes of
attractant using in vivo fluorescence resonance energy transfer measurements.
Specifically, we use a condensed representation of adaptation time courses for
efficient evaluation of different adaptation models. To quantitatively explain
the data, we finally develop a dynamic model for signaling and adaptation based
on the attractant flow in the experiment, signaling by cooperative receptor
complexes, and multiple layers of feedback regulation for adaptation. We
experimentally confirm the predicted effects of changing the enzyme-expression
level and bypassing the negative feedback for demethylation. Our data analysis
suggests significant imprecision in adaptation for large additions.
Furthermore, our model predicts highly regulated, ultrafast adaptation in
response to removal of attractant, which may be useful for fast reorientation
of the cell and noise reduction in adaptation.Comment: accepted for publication in PLoS Computational Biology; manuscript
(19 pages, 5 figures) and supplementary information; added additional
clarification on alternative adaptation models in supplementary informatio
Comorbid health conditions and their impact on social isolation, loneliness, quality of life, and well-being in people with dementia: longitudinal findings from the IDEAL programme
\ua9 2024, The Author(s).Background: Most people with dementia have multiple health conditions. This study explores (1) number and type of health condition(s) in people with dementia overall and in relation to age, sex, dementia type, and cognition; (2) change in number of health conditions over two years; and (3) whether over time the number of health conditions at baseline is related to social isolation, loneliness, quality of life, and/or well-being. Methods: Longitudinal data from the IDEAL (Improving the experience of Dementia and Enhancing Active Life) cohort were used. Participants comprised people with dementia (n = 1490) living in the community (at baseline) in Great Britain. Health conditions using the Charlson Comorbidity Index, cognition, social isolation, loneliness, quality of life, and well-being were assessed over two years. Mixed effects modelling was used. Results: On average participants had 1.8 health conditions at baseline, excluding dementia; increasing to 2.5 conditions over two years. Those with vascular dementia or mixed (Alzheimer’s and vascular) dementia had more health conditions than those with Alzheimer’s disease. People aged ≥ 80 had more health conditions than those aged < 65 years. At baseline having more health conditions was associated with increased loneliness, poorer quality of life, and poorer well-being, but was either minimally or not associated with cognition, sex, and social isolation. Number of health conditions had either minimal or no influence on these variables over time. Conclusions: People with dementia in IDEAL generally had multiple health conditions and those with more health conditions were lonelier, had poorer quality of life, and poorer well-being
An international comparative study of blood pressure in populations of European vs. African descent
Background: The consistent finding of higher prevalence of hypertension in US blacks compared
to whites has led to speculation that African-origin populations are particularly susceptible to this
condition. Large surveys now provide new information on this issue.
Methods: Using a standardized analysis strategy we examined prevalence estimates for 8 white
and 3 black populations (N = 85,000 participants).
Results: The range in hypertension prevalence was from 27 to 55% for whites and 14 to 44% for
blacks.
Conclusions: These data demonstrate that not only is there a wide variation in hypertension
prevalence among both racial groups, the rates among blacks are not unusually high when viewed
internationally. These data suggest that the impact of environmental factors among both
populations may have been under-appreciated
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Evaluating ‘living well’ with mild-to-moderate dementia: Co-production and validation of the IDEAL My Life Questionnaire
Data availability statement: The My Life Questionnaire is free to use. A printable version can be downloaded from the Living with Dementia Toolkit https://livingwithdementiatoolkit.org.uk/home/how-are-you-feeling-today/ or via this link https://medicine.exeter.ac.uk/reach/publications/. Requests for further information about the IDEAL My Life Questionnaire may be directed to [email protected]. IDEAL cohort data were deposited with the UK Data Archive in April 2020. Details of how to access the data can be found here: https://reshare.ukdataservice.ac.uk/854293/.Copyright © The Author(s) 2023.. Objectives:
We aimed to co-produce and validate an accessible, evidence-based questionnaire measuring ‘living well’ with dementia that reflects the experience of people with mild-to-moderate dementia.
Methods:
Nine people with dementia formed a co-production group. An initial series of workshops generated the format of the questionnaire and a longlist of items. Preliminary testing with 53 IDEAL cohort participants yielded a shortlist of items. These were tested with 136 IDEAL cohort participants during a further round of data collection and assessed for reliability and validity. The co-production group contributed to decisions throughout and agreed the final version.
Results:
An initial list of 230 items was reduced to 41 for initial testing, 12 for full testing, and 10 for the final version. The 10-item version had good internal consistency and test-retest reliability, and a single factor structure. Analyses showed significant large positive correlations with scores on measures of quality of life, well-being, and satisfaction with life, and expected patterns of association including a significant large negative association with depression scores and no association with cognitive test scores.
Conclusions:
The co-produced My Life Questionnaire is an accessible and valid measure of ‘living well’ with dementia suitable for use in a range of contexts.Economic and Social Research Council, National Institute for Health and Care Research (ES/L001853/2); Alzheimer's Society (348, AS-PR2-16-001)
Predicted Auxiliary Navigation Mechanism of Peritrichously Flagellated Chemotactic Bacteria
Chemotactic movement of Escherichia coli is one of the most thoroughly studied paradigms of simple behavior. Due to significant competitive advantage conferred by chemotaxis and to high evolution rates in bacteria, the chemotaxis system is expected to be strongly optimized. Bacteria follow gradients by performing temporal comparisons of chemoeffector concentrations along their runs, a strategy which is most efficient given their size and swimming speed. Concentration differences are detected by a sensory system and transmitted to modulate rotation of flagellar motors, decreasing the probability of a tumble and reorientation if the perceived concentration change during a run is positive. Such regulation of tumble probability is of itself sufficient to explain chemotactic drift of a population up the gradient, and is commonly assumed to be the only navigation mechanism of chemotactic E. coli. Here we use computer simulations to predict existence of an additional mechanism of gradient navigation in E. coli. Based on the experimentally observed dependence of cell tumbling angle on the number of switching motors, we suggest that not only the tumbling probability but also the degree of reorientation during a tumble depend on the swimming direction along the gradient. Although the difference in mean tumbling angles up and down the gradient predicted by our model is small, it results in a dramatic enhancement of the cellular drift velocity along the gradient. We thus demonstrate a new level of optimization in E. coli chemotaxis, which arises from the switching of several flagellar motors and a resulting fine tuning of tumbling angle. Similar strategy is likely to be used by other peritrichously flagellated bacteria, and indicates yet another level of evolutionary development of bacterial chemotaxis
Investigating effects of parasite infection on body condition of the Kafue lechwe (Kobus leche kafuensis) in the Kafue basin
<p>Abstract</p> <p>Background</p> <p>The Kafue lechwe (<it>Kobus leche Kafuensis</it>), a medium-sized semi-aquatic antelope, is endemic to the Kafue basin of Zambia. The population of the Kafue lechwe has significantly dropped in the last decades leading to its subsequent inclusion on the red list of endangered species. In order to save the remaining population from extinction, it has become increasingly important that the impact of parasite infection and infestation on the Kafue lechwe is investigated.</p> <p>Findings</p> <p>Endoparasites accounted for the majority of parasites observed from a study of 40 Kafue lechwe occurring in the the Kafue basin. <it>Amphistoma spp. </it>were present in all animals examined, while <it>Fasciola gigantica </it>had a prevalence rate of 0.525 (95% CI: 0.36 to 0.69) and species of <it>Schistosoma </it>0.3 (95% CI: 0.15 to 0.45). Among the ectoparasites, <it>Strobiloestrous vanzyli</it>, had a prevalence rate of 0.15 (95% CI: 0.03 to 0.27), while <it>Rhipicephalus appendiculatus </it>had a prevalence of 0.075 (3/40). Our findings indicate that body condition was not influenced by the parasitic infestation in Kafue lechwe. There was no association between sex and parasitic burden (odds ratio = 0.3, 95% CI: 0.8-1.3). However, an association between age and parasitic burden was observed as older animals above 15 years were more likely to get parasite infections than those aged between 1-5 years (odds ratio = 1.5, 95% CI: 1.1-2.4).</p> <p>Conclusion</p> <p>Overall, there was no evidence that parasitic infections and infestations adversely affected the lechwe population on the Kafue basin. These findings indicate that ecto- and endo-parasite infestation might not play a significant role in reducing the Kafue lechwe population on the Kafue basin.</p
A Naturally Occurring Mutation in ropB Suppresses SpeB Expression and Reduces M1T1 Group A Streptococcal Systemic Virulence
Epidemiological studies of group A streptococcus (GAS) have noted an inverse relationship between SpeB expression and invasive disease. However, the role of SpeB in the course of infection is still unclear. In this study we utilize a SpeB-negative M1T1 clinical isolate, 5628, with a naturally occurring mutation in the gene encoding the regulator RopB, to elucidate the role of RopB and SpeB in systemic virulence. Allelic exchange mutagenesis was used to replace the mutated ropB allele in 5628 with the intact allele from the well characterized isolate 5448. The inverse allelic exchange was also performed to replace the intact ropB in 5448 with the mutated allele from 5628. An intact ropB was found to be essential for SpeB expression. While the ropB mutation was shown to have no effect on hemolysis of RBC's, extracellular DNase activity or survival in the presence of neutrophils, strains with the mutated ropB allele were less virulent in murine systemic models of infection. An isogenic SpeB knockout strain containing an intact RopB showed similarly reduced virulence. Microarray analysis found genes of the SpeB operon to be the primary target of RopB regulation. These data show that an intact RopB and efficient SpeB production are necessary for systemic infection with GAS
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