9,122 research outputs found
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
On the particle paths and the stagnation points in small-amplitude deep-water waves
In order to obtain quite precise information about the shape of the particle
paths below small-amplitude gravity waves travelling on irrotational deep
water, analytic solutions of the nonlinear differential equation system
describing the particle motion are provided. All these solutions are not closed
curves. Some particle trajectories are peakon-like, others can be expressed
with the aid of the Jacobi elliptic functions or with the aid of the
hyperelliptic functions. Remarks on the stagnation points of the
small-amplitude irrotational deep-water waves are also made.Comment: to appear in J. Math. Fluid Mech. arXiv admin note: text overlap with
arXiv:1106.382
NASA ACTS Satellite: A Disaster Recovery Test
In September 1993, NASA launched its long-awaited Advanced Communication Technology (ACTS) satellite. ACTS is a 17 billion regional bank with 338 offices in fourteen states. Transactions on HNB\u27s data networks currently travel on terrestrial T-1 lines. The Ohio University/HNB tests were initiated to determine the capability of the satellite for service restoral in the case of a failure in one of the Bank\u27s terrestrial links.
The ACTS Disaster Recovery Project was designed to test the Bank\u27s ability to by-pass such problems on the ground by switching to a space path. The goal was to make the switch-over with the briefest interuption of service, with minimal loss of transmitted data, within acceptable cost and with sustained security
Morphogen Transport in Epithelia
We present a general theoretical framework to discuss mechanisms of morphogen
transport and gradient formation in a cell layer. Trafficking events on the
cellular scale lead to transport on larger scales. We discuss in particular the
case of transcytosis where morphogens undergo repeated rounds of
internalization into cells and recycling. Based on a description on the
cellular scale, we derive effective nonlinear transport equations in one and
two dimensions which are valid on larger scales. We derive analytic expressions
for the concentration dependence of the effective diffusion coefficient and the
effective degradation rate. We discuss the effects of a directional bias on
morphogen transport and those of the coupling of the morphogen and receptor
kinetics. Furthermore, we discuss general properties of cellular transport
processes such as the robustness of gradients and relate our results to recent
experiments on the morphogen Decapentaplegic (Dpp) that acts in the fruit fly
Drosophila
Self-organization and Mechanical Properties of Active Filament Bundles
A phenomenological description for active bundles of polar filaments is
presented. The activity of the bundle results from crosslinks, that induce
relative displacements between the aligned filaments. Our generic description
is based on momentum conservation within the bundle. By specifying the internal
forces, a simple minimal model for the bundle dynamics is obtained, capturing
generic dynamic behaviors. In particular, contracted states as well as solitary
and oscillatory waves appear through dynamic instabilities. The introduction of
filament adhesion leads to self-organized persistent filament transport.
Furthermore, calculating the tension, homogeneous bundles are shown to be able
to actively contract and to perform work against external forces. Our
description is motivated by dynamic phenomena in the cytoskeleton and could
apply to stress-fibers and self-organization phenomena during cell-locomotion.Comment: 19 pages, 10 figure
A stochastic model of Min oscillations in Escherichia coli and Min protein segregation during cell division
The Min system in Escherichia coli directs division to the centre of the cell
through pole-to-pole oscillations of the MinCDE proteins. We present a one
dimensional stochastic model of these oscillations which incorporates membrane
polymerisation of MinD into linear chains. This model reproduces much of the
observed phenomenology of the Min system, including pole-to-pole oscillations
of the Min proteins. We then apply this model to investigate the Min system
during cell division. Oscillations continue initially unaffected by the closing
septum, before cutting off rapidly. The fractions of Min proteins in the
daughter cells vary widely, from 50%-50% up to 85%-15% of the total from the
parent cell, suggesting that there may be another mechanism for regulating
these levels in vivo.Comment: 19 pages, 12 figures (25 figure files); published at
http://www.iop.org/EJ/journal/physbi
Malignant minor salivary gland tumors: a retrospective study of 27 cases
PURPOSE: Malignant tumors of the intra-oral minor salivary glands are uncommon. The aim of this study was to give information concerning the clinical features of these tumors, the distribution of location, treatment opportunities, and outcome. METHODS: Twenty-seven patients with malignant salivary gland tumors that were treated between January 1999 and December 2008 were evaluated retrospectively. RESULTS: Of the 27 minor salivary gland carcinomas, 48.1% were adenoid cystic carcinomas (ACC), 29.7% mucoepidermoid carcinomas (MEC), 22.2% adenocarcinomas (ADCA). The most common first symptom was a painless swelling in 60% of the cases, with the second most common symptom being ulcers (28%). Four recurrences and two metastases were found. No recurrence was observed in ADCA. All four patients experiencing a recurrence developed it in the first 3 years after treatment. CONCLUSION: Wide excision with a clinical margin of 1 cm and in large tumors, positive surgical margins or perineural infiltration and postoperative radiotherapy (RT) can be recommended; but in order to give exact information concerning the possible benefit from postoperative RT, it needs large prospective multicenter studies. Long-term follow-up controls and in particularly longer than 5 years in ACC including yearly chest X-rays should be offered to these patients because of late metastasis and recurrences
Spontaneous waves in muscle fibres
Mechanical oscillations are important for many cellular processes, e.g. the
beating of cilia and flagella or the sensation of sound by hair cells. These
dynamic states originate from spontaneous oscillations of molecular motors. A
particularly clear example of such oscillations has been observed in muscle
fibers under non-physiological conditions. In that case, motor oscillations
lead to contraction waves along the fiber. By a macroscopic analysis of muscle
fiber dynamics we find that the spontaneous waves involve non-hydrodynamic
modes. A simple microscopic model of sarcomere dynamics highlights mechanical
aspects of the motor dynamics and fits with the experimental observations.Comment: 14 pages, 9 figure
Cavity Assisted Nondestructive Laser Cooling of Atomic Qubits
We analyze two configurations for laser cooling of neutral atoms whose
internal states store qubits. The atoms are trapped in an optical lattice which
is placed inside a cavity. We show that the coupling of the atoms to the damped
cavity mode can provide a mechanism which leads to cooling of the motion
without destroying the quantum information.Comment: 12 page
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