25,301 research outputs found
YoeB toxin is activated during thermal stress.
Type II toxin-antitoxin (TA) modules are thought to mediate stress-responses by temporarily suppressing protein synthesis while cells redirect transcription to adapt to environmental change. Here, we show that YoeB, a ribosome-dependent mRNase toxin, is activated in Escherichia coli cells grown at elevated temperatures. YoeB activation is dependent on Lon protease, suggesting that thermal stress promotes increased degradation of the YefM antitoxin. Though YefM is efficiently degraded in response to Lon overproduction, we find that Lon antigen levels do not increase during heat shock, indicating that another mechanism accounts for temperature-induced YefM proteolysis. These observations suggest that YefM/YoeB functions in adaptation to temperature stress. However, this response is distinct from previously described models of TA function. First, YoeB mRNase activity is maintained over several hours of culture at 42°C, indicating that thermal activation is not transient. Moreover, heat-activated YoeB does not induce growth arrest nor does it suppress global protein synthesis. In fact, E. coli cells proliferate more rapidly at elevated temperatures and instantaneously accelerate their growth rate in response to acute heat shock. We propose that heat-activated YoeB may serve a quality control function, facilitating the recycling of stalled translation complexes through ribosome rescue pathways
A Search for Intrinsic Polarization in O Stars with Variable Winds
New observations of 9 of the brightest northern O stars have been made with
the Breger polarimeter on the 0.9~m telescope at McDonald Observatory and the
AnyPol polarimeter on the 0.4~m telescope at Limber Observatory, using the
Johnson-Cousins UBVRI broadband filter system. Comparison with earlier
measurements shows no clearly defined long-term polarization variability. For
all 9 stars the wavelength dependence of the degree of polarization in the
optical range can be fit by a normal interstellar polarization law. The
polarization position angles are practically constant with wavelength and are
consistent with those of neighboring stars. Thus the simplest conclusion is
that the polarization of all the program stars is primarily interstellar.
The O stars chosen for this study are generally known from ultraviolet and
optical spectroscopy to have substantial mass loss rates and variable winds, as
well as occasional circumstellar emission. Their lack of intrinsic polarization
in comparison with the similar Be stars may be explained by the dominance of
radiation as a wind driving force due to higher luminosity, which results in
lower density and less rotational flattening in the electron scattering inner
envelopes where the polarization is produced. However, time series of
polarization measurements taken simultaneously with H-alpha and UV spectroscopy
during several coordinated multiwavelength campaigns suggest two cases of
possible small-amplitude, periodic short-term polarization variability, and
therefore intrinsic polarization, which may be correlated with the more widely
recognized spectroscopic variations.Comment: LaTeX2e, 22 pages including 11 tables; 12 separate gif figures; uses
aastex.cls preprint package; accepted by The Astronomical Journa
Multi-Behavioral Endpoint Testing Of An 87-Chemical Compound Library In Freshwater Planarians
There is an increased recognition in the field of toxicology of the value of medium-to-high-throughput screening methods using in vitro and alternative animal models. We have previously introduced the asexual freshwater planarian Dugesia japonica as a new alternative animal model and proposed that it is particularly well-suited for the study of developmental neurotoxicology. In this paper, we discuss how we have expanded and automated our screening methodology to allow for fast screening of multiple behavioral endpoints, developmental toxicity, and mortality. Using an 87-compound library provided by the National Toxicology Program (NTP), consisting of known and suspected neurotoxicants, including drugs, flame retardants, industrial chemicals, polycyclic aromatic hydrocarbons (PAHs), pesticides and presumptive negative controls, we further evaluate the benefits and limitations of the system for medium-throughput screening, focusing on the technical aspects of the system. We show that, in the context of this library, planarians are the most sensitive to pesticides with 16/16 compounds causing toxicity and the least sensitive to PAHs, with only 5/17 causing toxicity. Furthermore, while none of the presumptive negative controls were bioactive in adult planarians, 2/5, acetaminophen and acetylsalicylic acid, were bioactive in regenerating worms. Notably, these compounds were previously reported as developmentally toxic in mammalian studies. Through parallel screening of adults and developing animals, planarians are thus a useful model to detect such developmental-specific effects, which was observed for 13 chemicals in this library. We use the data and experience gained from this screen to propose guidelines for best practices when using planarians for toxicology screens
Completeness and Incompleteness of Synchronous Kleene Algebra
Synchronous Kleene algebra (SKA), an extension of Kleene algebra (KA), was
proposed by Prisacariu as a tool for reasoning about programs that may execute
synchronously, i.e., in lock-step. We provide a countermodel witnessing that
the axioms of SKA are incomplete w.r.t. its language semantics, by exploiting a
lack of interaction between the synchronous product operator and the Kleene
star. We then propose an alternative set of axioms for SKA, based on Salomaa's
axiomatisation of regular languages, and show that these provide a sound and
complete characterisation w.r.t. the original language semantics.Comment: Accepted at MPC 201
A heralded quantum gate between remote quantum memories
We demonstrate a probabilistic entangling quantum gate between two distant
trapped ytterbium ions. The gate is implemented between the hyperfine "clock"
state atomic qubits and mediated by the interference of two emitted photons
carrying frequency encoded qubits. Heralded by the coincidence detection of
these two photons, the gate has an average fidelity of 90+-2%. This entangling
gate together with single qubit operations is sufficient to generate large
entangled cluster states for scalable quantum computing
Exoplanetary atmosphere target selection in the era of comparative planetology
The large number of new planets expected from wide-area transit surveys means
that follow-up transmission spectroscopy studies of their atmospheres will be
limited by the availability of telescope assets. We argue that telescopes
covering a broad range of apertures will be required, with even 1m-class
instruments providing a potentially important contribution. Survey strategies
that employ automated target selection will enable robust population studies.
As part of such a strategy, we propose a decision metric to pair the best
target to the most suitable telescope, and demonstrate its effectiveness even
when only primary transit observables are available. Transmission spectroscopy
target selection need not therefore be impeded by the bottle-neck of requiring
prior follow-up observations to determine the planet mass. The decision metric
can be easily deployed within a distributed heterogeneous network of telescopes
equipped to undertake either broadband photometry or spectroscopy. We show how
the metric can be used either to optimise the observing strategy for a given
telescope (e.g. choice of filter) or to enable the selection of the best
telescope to optimise the overall sample size. Our decision metric can also
provide the basis for a selection function to help evaluate the statistical
completeness of follow-up transmission spectroscopy datasets. Finally, we
validate our metric by comparing its ranked set of targets against lists of
planets that have had their atmospheres successfully probed, and against some
existing prioritised exoplanet lists.Comment: 20 pages, 16 figures, 3 tables. Revision 3, accepted by MNRAS.
Improvements include always using planetary masses where available and
reliable, treatment for sky backgrounds and out-of-transit noise and a use
case for defocused photometr
Travelling Salesman Problem with a Center
We study a travelling salesman problem where the path is optimized with a
cost function that includes its length as well as a certain measure of
its distance from the geometrical center of the graph. Using simulated
annealing (SA) we show that such a problem has a transition point that
separates two phases differing in the scaling behaviour of and , in
efficiency of SA, and in the shape of minimal paths.Comment: 4 pages, minor changes, accepted in Phys.Rev.
Network recovery from massive failures under uncertain knowledge of damages
This paper addresses progressive network recovery under uncertain knowledge of damages. We formulate the problem as a mixed integer linear programming (MILP), and show that it is NP-Hard. We propose an iterative stochastic recovery algorithm (ISR) to recover the network in a progressive manner to satisfy the critical services. At each optimization step, we make a decision to repair a part of the network and gather more information iteratively, until critical services are completely restored. Three different algorithms are used to find a feasible set and determine which node to repair, namely, 1) an iterative shortest path algorithm (ISR-SRT), 2) an approximate branch and bound (ISR-BB) and 3) an iterative multi-commodity LP relaxation (ISR-MULT). Further, we have modified the state-of-the-Art iterative split and prune (ISP) algorithm to incorporate the uncertain failures. Our results show that ISR-BB and ISR- MULT outperform the state-of-the-Art 'progressive ISP' algorithm while we can configure our choice of trade-off between the execution time, number of repairs (cost) and the demand loss. We show that our recovery algorithm, on average, can reduce the total number of repairs by a factor of about 3 with respect to ISP, while satisfying all critical deman
Coherent Error Suppression in Multi-Qubit Entangling Gates
We demonstrate a simple pulse shaping technique designed to improve the
fidelity of spin-dependent force operations commonly used to implement
entangling gates in trapped-ion systems. This extension of the
M{\o}lmer-S{\o}rensen gate can theoretically suppress the effects of certain
frequency and timing errors to any desired order and is demonstrated through
Walsh modulation of a two-qubit entangling gate on trapped atomic ions. The
technique is applicable to any system of qubits coupled through collective
harmonic oscillator modes
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