2,695 research outputs found
Stuttering Min oscillations within E. coli bacteria: A stochastic polymerization model
We have developed a 3D off-lattice stochastic polymerization model to study
subcellular oscillation of Min proteins in the bacteria Escherichia coli, and
used it to investigate the experimental phenomenon of Min oscillation
stuttering. Stuttering was affected by the rate of immediate rebinding of MinE
released from depolymerizing filament tips (processivity), protection of
depolymerizing filament tips from MinD binding, and fragmentation of MinD
filaments due to MinE. Each of processivity, protection, and fragmentation
reduces stuttering, speeds oscillations, and reduces MinD filament lengths.
Neither processivity or tip-protection were, on their own, sufficient to
produce fast stutter-free oscillations. While filament fragmentation could, on
its own, lead to fast oscillations with infrequent stuttering; high levels of
fragmentation degraded oscillations. The infrequent stuttering observed in
standard Min oscillations are consistent with short filaments of MinD, while we
expect that mutants that exhibit higher stuttering frequencies will exhibit
longer MinD filaments. Increased stuttering rate may be a useful diagnostic to
find observable MinD polymerization in experimental conditions.Comment: 21 pages, 7 figures, missing unit for k_f inserte
New Internal Stress Driven on-Chip Micromachines for Extracting Mechanical Properties of Thin Films
A new concept of micromachines has been developed for measuring the
mechanical properties of thin metallic films. The actuator is a beam undergoing
large internal stresses built up during the deposition process. Al thin films
are deposited partly on the actuator beam and on the substrate. By etching the
structure, the actuator contracts and pulls the Al film. Full stress strain
curves can be generated by designing a set of micromachines with various
actuator lengths. In the present study, the displacements have been measured by
scanning electronic microscopy. The stress is derived from simple continuum
mechanics relationships. The tensile properties of Al films of various
thicknesses have been tested. A marked increase of the strength with decreasing
film thickness is observed.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Min-oscillations in Escherichia coli induced by interactions of membrane-bound proteins
During division it is of primary importance for a cell to correctly determine
the site of cleavage. The bacterium Escherichia coli divides in the center,
producing two daughter cells of equal size. Selection of the center as the
correct division site is in part achieved by the Min-proteins. They oscillate
between the two cell poles and thereby prevent division at these locations.
Here, a phenomenological description for these oscillations is presented, where
lateral interactions between proteins on the cell membrane play a key role.
Solutions to the dynamic equations are compared to experimental findings. In
particular, the temporal period of the oscillations is measured as a function
of the cell length and found to be compatible with the theoretical prediction.Comment: 17 pages, 5 figures. Submitted to Physical Biolog
The Rarita-Schwinger spin-3/2 equation in a nonuniform, central potential
The equations of motion for a massive spin-3/2 Rarita-Schwinger field in a
finite-range, central, Lorentz scalar potential are developed. It is shown that
the resulting density may not be everywhere positive definite.Comment: 9 pages, RevTe
The effect of interactions between a bacterial strain isolated from drinking water and a pathogen surrogate on biofilms formation diverged under static vs flow conditions
AimsInteractions with water bacteria affect the incorporation of pathogens into biofilms and thus pathogen control in drinking water systems. This study was to examine the impact of static vs flow conditions on interactions between a pathogen and a water bacterium on pathogen biofilm formation under laboratory settings.Methods and ResultsA pathogen surrogate Escherichia coli and a drinking water isolate Stenotrophomonas maltophilia was selected for this study. Biofilm growth was examined under two distinct conditions, in flow cells with continuous medium supply vs in static microtitre plates with batch culture. E. coli biofilm was greatly stimulated (c. 2–1000 times faster) with the presence of S. maltophilia in flow cells, but surprisingly inhibited (c. 65–95% less biomass) in microtitre plates. These divergent effects were explained through various aspects including surface attachment, cellular growth, extracellular signals and autoaggregation.ConclusionsInteractions with the same water bacterium resulted in different effects on E. coli biofilm formation when culture conditions changed from static to flow.Significance and Impact of StudyThis study highlights the complexity of species interactions on biofilm formation and suggests that environmental conditions such as the flow regime can be taken into consideration for the management of microbial contamination in drinking water systems.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140002/1/jam13596.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/140002/2/jam13596_am.pd
High-frequency performance of Schottky source/drain silicon pMOS devices
A radio-frequency performance of 85-nm gate-length p-type Schottky barrier (SB) with PtSi source/drain materials is investigated. The impact of silicidation annealing temperature on the high-frequency behavior of SB MOSFETs is analyzed using an extrinsic small-signal equivalent circuit. It is demonstrated that the current drive and the gate transconductance strongly depend on the silicidation anneal temperature, whereas the unity-gain cutoff frequency of the measured devices remains nearly unchanged
Neurosurgical management of non-spastic movement disorders
BACKGROUND: Non-spastic movement disorders in children are common, although true epidemiologic data is difficult to ascertain. Children are more likely than adults to have hyperkinetic movement disorders defined as tics, dystonia, chorea/athetosis, or tremor. These conditions manifest from acquired or heredodegenerative etiologies and often severely limit function despite medical and surgical management paradigms. Neurosurgical management for these conditions is highlighted.
METHODS: We performed a focused review of the literature by searching PubMed on 16 May 2023 using key terms related to our review. No temporal filter was applied, but only English articles were considered. We searched for the terms (( Pallidotomy [Mesh]) OR Rhizotomy [Mesh]) OR Deep Brain Stimulation [Mesh], dystonia, children, adolescent, pediatric, globus pallidus, in combination. All articles were reviewed for inclusion in the final reference list.
RESULTS: Our search terms returned 37 articles from 2004 to 2023. Articles covering deep brain stimulation were the most common (n = 34) followed by pallidotomy (n = 3); there were no articles on rhizotomy.
DISCUSSION: Non-spastic movement disorders are common in children and difficult to treat. Most of these patients are referred to neurosurgery for the management of dystonia, with modern neurosurgical management including pallidotomy, rhizotomy, and deep brain stimulation. Historically, pallidotomy has been effective and may still be preferred in subpopulations presenting either in status dystonicus or with high risk for hardware complications. Superiority of DBS over pallidotomy for secondary dystonia has not been determined. Rhizotomy is an underutilized surgical tool and more study characterizing efficacy and risk profile is indicated
Predictions from a stochastic polymer model for the MinDE dynamics in E.coli
The spatiotemporal oscillations of the Min proteins in the bacterium
Escherichia coli play an important role in cell division. A number of different
models have been proposed to explain the dynamics from the underlying
biochemistry. Here, we extend a previously described discrete polymer model
from a deterministic to a stochastic formulation. We express the stochastic
evolution of the oscillatory system as a map from the probability distribution
of maximum polymer length in one period of the oscillation to the probability
distribution of maximum polymer length half a period later and solve for the
fixed point of the map with a combined analytical and numerical technique. This
solution gives a theoretical prediction of the distributions of both lengths of
the polar MinD zones and periods of oscillations -- both of which are
experimentally measurable. The model provides an interesting example of a
stochastic hybrid system that is, in some limits, analytically tractable.Comment: 16 page
The HERMES Solar Atlas and the spectroscopic analysis of the seismic solar analogue KIC3241581
Solar-analog stars provide an excellent opportunity to study the Sun's
evolution, i.e. the changes with time in stellar structure, activity, or
rotation for solar-like stars. The unparalleled photometric data from the NASA
space telescope Kepler allows us to study and characterise solar-like stars
through asteroseismology. We aim to spectroscopically investigate the
fundamental parameter and chromospheric activity of solar analogues and twins,
based on observations obtained with the HERMES spectrograph and combine them
with asteroseismology. Therefore, we need to build a solar atlas for the
spectrograph, to provide accurate calibrations of the spectroscopically
determined abundances of solar and late type stars observed with this
instrument and thus perform differential spectral comparisons. We acquire
high-resolution and high signal-to-noise spectroscopy to construct three solar
reference spectra by observing the reflected light of Vesta and Victoria
asteroids and Europa (100<S/N<450) with the \Hermes spectrograph. We then
observe the Kepler solar analog KIC3241581 (S/N~170). We constructed three
solar spectrum atlases from 385 to 900 nm obtained with the Hermes spectrograph
from observations of two bright asteroids and Europa. A comparison between our
solar spectra atlas to the Kurucz and HARPS solar spectrum shows an excellent
agreement. KIC3241581 was found to be a long-periodic binary system. The
fundamental parameter for the stellar primary component are Teff=5689+/-11K,
logg=4.385+/-0.005, [Fe/H]=+0.22+/-0.01, being in agreement with the published
global seismic values confirming its status of solar analogue. KIC 3241581 is a
metal rich solar analogue with a solar-like activity level in a binary system
of unknown period. The chromospheric activity level is compatible to the solar
magnetic activity.Comment: 12 pages, 8 figures, accepted for publication in A&
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