13,457 research outputs found
Noise characteristics of the Escherichia coli rotary motor
The chemotaxis pathway in the bacterium Escherichia coli allows cells to
detect changes in external ligand concentration (e.g. nutrients). The pathway
regulates the flagellated rotary motors and hence the cells' swimming
behaviour, steering them towards more favourable environments. While the
molecular components are well characterised, the motor behaviour measured by
tethered cell experiments has been difficult to interpret. Here, we study the
effects of sensing and signalling noise on the motor behaviour. Specifically,
we consider fluctuations stemming from ligand concentration, receptor switching
between their signalling states, adaptation, modification of proteins by
phosphorylation, and motor switching between its two rotational states. We
develop a model which includes all signalling steps in the pathway, and discuss
a simplified version, which captures the essential features of the full model.
We find that the noise characteristics of the motor contain signatures from all
these processes, albeit with varying magnitudes. This allows us to address how
cell-to-cell variation affects motor behaviour and the question of optimal
pathway design. A similar comprehensive analysis can be applied to other
two-component signalling pathways.Comment: 22 pages, 7 figures, 3 tutorials, supplementary information;
submitted manuscrip
Electronic Study Books and learning style
Attention has been drawn to the concepts of Electronic Books and Electronic Study Books. Several publications have discussed some main ideas (paradigms) for both concepts. For the Electronic Study Book as a learning environment, it is essential to consider individual modes of learning, usually termed 'learning styles'. It is argued that Electronic Study Books should be adaptable in accordance with personal learning styles. Some options will be presented to link 'styles' and 'books'. One such option is a Style Initiating Module which we are currently investigating
Strengthening Community Colleges' Influence on Economic Mobility
Examines the role of community colleges in enhancing upward mobility. Compares family incomes of community college and four-year college students and incomes by degree attained. Recommends ways to help more students obtain degrees in high-earning fields
Fatal heart block from intentional yew tree (Taxus baccata) ingestion: a case report
© The Author(s) 2019. Published by Oxford University Press on behalf of the European Society of Cardiology. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited.BackgroundâTaxus baccata, also known as English yew, is a poison that causes cardiac arrhythmias and can result in death from cardiogenic shock.Case summaryâA 49-year-old gentleman was admitted following yew ingestion with suicidal intent. He was bradycardic at 30 b.p.m. and hypotensive on arrival. Electrocardiography revealed complete heart block with broad complex ventricular escape rate of 30 b.p.m. Bedside echocardiography revealed severe global impairment of right and left ventricular systolic function. Urgent temporary transvenous pacing was instituted, and the patient was considered for veno-arterial extracorporeal membrane oxygenation. Unfortunately, he deteriorated rapidly and cardiorespiratory arrest ensued, and despite prolonged in-hospital resuscitation, the patient died. Post-mortem examination revealed small needle-shaped plant leaves together with seeds found in the stomach. Ante mortem serum sample analysis sent to the Royal Botanical Gardens and revealed the presence of taxine Type B alkaloids in the patientâs blood.DiscussionâYew poisoning is a rare occurrence, and there is currently no effective antidote. Treatment involves supportive management, comprising prolonged effective cardiopulmonary resuscitation, pacing, and mechanical cardiac support. This case illustrates the importance of prompt recognition of yew poisoning, alongside early consideration of pacing and mechanical cardiac support. Due to the rarity of this cause of heart block, and since patients may not always volunteer a history of yew ingestion, yew poisoning is something that physicians should be aware of and this should be considered in the differential diagnosis in patients with unexpected heart block. Serum analysis for taxine alkaloids can be used to confirm the diagnosis.Peer reviewe
Massless Interacting Scalar Fields in de Sitter space
We present a method to compute the two-point functions for an scalar
field model in de Sitter spacetime, avoiding the well known infrared problems
for massless fields. The method is based on an exact treatment of the Euclidean
zero modes and a perturbative one of the nonzero modes, and involves a partial
resummation of the leading secular terms. This resummation, crucial to obtain a
decay of the correlation functions, is implemented along with a double
expansion in an effective coupling constant and in . The
results reduce to those known in the leading infrared approximation and
coincide with the ones obtained directly in Lorentzian de Sitter spacetime in
the large limit. The new method allows for a systematic calculation of
higher order corrections both in and in .Comment: 8 pages. Summarized version of JHEP 09 (2016) 117 [arXiv:1606.03481].
Published in the Proceedings of the 19th International Seminar on High Energy
Physics (QUARKS-2016
model in Euclidean de Sitter space: beyond the leading infrared approximation
We consider an scalar field model with quartic interaction in
-dimensional Euclidean de Sitter space. In order to avoid the problems of
the standard perturbative calculations for light and massless fields, we
generalize to the theory a systematic method introduced previously for a
single field, which treats the zero modes exactly and the nonzero modes
perturbatively. We compute the two-point functions taking into account not only
the leading infrared contribution, coming from the self-interaction of the zero
modes, but also corrections due to the interaction of the ultraviolet modes.
For the model defined in the corresponding Lorentzian de Sitter spacetime, we
obtain the two-point functions by analytical continuation. We point out that a
partial resummation of the leading secular terms (which necessarily involves
nonzero modes) is required to obtain a decay at large distances for massless
fields. We implement this resummation along with a systematic double expansion
in an effective coupling constant and in 1/N. We explicitly
perform the calculation up to the next-to-next-to-leading order in
and up to next-to-leading order in 1/N. The results reduce to
those known in the leading infrared approximation. We also show that they
coincide with the ones obtained directly in Lorentzian de Sitter spacetime in
the large N limit, provided the same renormalization scheme is used.Comment: 31 pages, 5 figures. Minor changes. Published versio
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