152 research outputs found
Two fault tolerant toggle-hook release
A coupling device is disclosed which is mechanically two fault tolerant for release. The device comprises a fastener plate and fastener body, each of which is attachable to a different one of a pair of structures to be joined. The fastener plate and body are coupled by an elongate toggle mounted at one end in a socket on the fastener plate for universal pivotal movement thereon. The other end of the toggle is received in an opening in the fastener body and adapted for limited pivotal movement therein. The toggle is adapted to be restrained by three latch hooks arranged in symmetrical equiangular spacing about the axis of the toggle, each hook being mounted on the fastener body for pivotal movement between an unlatching non-contact position with respect to the toggle and a latching position in engagement with a latching surface of the toggle. The device includes releasable lock means for locking each latch hook in its latching position whereby the toggle couples the fastener plate to the fastener body and means for releasing the lock means to unlock each said latch hook from the latch position whereby the unlocking of at least one of the latch hooks from its latching position results in the decoupling of the fastener plate from the fastener body
Corrigendum: Co-adaptation of Streptococcus mutans to simulated microgravity and silver nitrate
Co-adaptation of Streptococcus mutans to simulated microgravity and silver nitrate
To sustain life on extended space missions, it is essential to maintain clean potable water. NASA currently uses iodine as the primary biocide in the potable water dispenser on the International Space Station and has recently proposed a potential switch to silver-based antimicrobials. Streptococcus mutans is the primary etiological agent of dental caries, part of the normal oral flora, and would endure direct exposure to water from the potable water dispenser. In our previous work, we examined the 100-day adaptive response of Streptococcus mutans to simulated microgravity (sMG). Here, we examined the evolutionary co-adaptation of S. mutans under sMG and silver nitrate (AgNO3) to evaluate the consequences of using silver as a primary biocide in space and the impact on the evolution of microbes from the oral microbiome. To do this, we adapted four populations of S. mutans under sMG and co-adapted four populations in simulated microgravity and silver nitrate using high-aspect ratio vessels for 100 days. Genomic analysis at multiple time points showed that S. mutans in sMG evolved variants consistent with our previous findings (SMU_1307c and SMU_399) while also acquiring novel mutations in the glutathione reductase gorA. The co-adapted populations showed mutations specific for the environment in ciaH/R, PBP1a, trkA, and trkB. We also assessed virulence phenotypes, and while simulated microgravity increased antibiotic susceptibility, sucrose-dependent adhesion, and, in some populations, acid tolerance, co-adaptation to silver nitrate reversed these effects. Overall, these data show that the use of silver as a biocide in simulated microgravity can evolve strains with novel genotypic and phenotypic traits that could alter virulence
Genotype-by-environment interactions govern fitness changes associated with adaptive mutations in two-component response systems
Introduction: Two-component response systems (TCRS) are the main mechanism by which prokaryotes acclimate to changing environments. These systems are composed of a membrane bound histidine kinase (HK) that senses external signals and a response regulator (RR) that activates transcription of response genes. Despite their known role in acclimation, little is known about the role TCRS play in environmental adaptation. Several experimental evolution studies have shown the acquisition of mutations in TCRS during adaptation, therefore here we set out to characterize the adaptive mechanism resulting from these mutations and evaluate whether single nucleotide changes in one gene could induce variable genotype-by-environment (GxE) interactions.Methods: To do this, we assessed fitness changes and differential gene expression for four adaptive mutations in cusS, the gene that encodes the HK CusS, acquired by Escherichia coli during silver adaptation.Results: Fitness assays showed that as the environment changed, each mutant displayed a unique fitness profile with greatest fitness in the original selection environment. RNAseq then indicated that, in ± silver nitrate, each mutant induces a primary response that upregulates cusS, its RR cusR, and constitutively expresses the target response genes cusCFBA. This then induces a secondary response via differential expression of genes regulated by the CusR through TCRS crosstalk. Finally, each mutant undergoes fitness tuning through unique tertiary responses that result in gene expression patterns specific for the genotype, the environment and optimized for the original selection conditions.Discussion: This three-step response shows that different mutations in a single gene leads to individualized phenotypes governed by unique GxE interactions that not only contribute to transcriptional divergence but also to phenotypic plasticity
A simple model for AGN feedback in nearby early-type galaxies
Recent work indicates that star-forming early-type galaxies (ETGs) residing
in the blue cloud migrate rapidly to the red sequence within around a Gyr,
passing through several phases of increasingly strong AGN activity in the
process (Schawinski et al. 2007, MNRAS, 382, 1415; S07 hereafter). We show that
natural depletion of the gas reservoir through star formation (i.e. in the
absence of any feedback from the AGN) induces a blue-to-red reddening rate that
is several factors lower than that observed in S07. This is because the gas
depletion rate due to star formation alone is too slow, implying that another
process needs to be invoked to remove gas from the system and accelerate the
reddening rate. We develop a simple phenomenological model, in which a fraction
of the AGN's luminosity couples to the gas reservoir over a certain 'feedback
timescale' and removes part of the gas mass from the galaxy, while the
remaining gas continues to contribute to star formation. We use the model to
investigate scenarios which yield migration times consistent with the results
of S07. We find that acceptable models have feedback timescales <0.2 Gyrs. The
mass fraction in young stars in the remnants is <5% and the residual gas
fractions are less than 0.6%, in good agreement with the recent literature. At
least half of the initial gas reservoir is removed as the galaxies evolve from
the blue cloud to the red sequence. If we restrict ourselves to feedback
timescales similar to the typical duty cycles of local AGN (a few hundred Myrs)
then a few tenths of a percent of the luminosity of an early-type Seyfert
(10^11 LSun) must couple to the gas reservoir in order to produce migration
times that are consistent with the observations.Comment: MNRAS in press (minor revisions to version 1
Anatomy of a post-starburst minor merger: a multi-wavelength WFC3 study of NGC 4150
(Abridged) We present a spatially-resolved near-UV/optical study of NGC 4150,
using the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope.
Previous studies of this early-type galaxy (ETG) indicate that it has a large
reservoir of molecular gas, exhibits a kinematically decoupled core (likely
indication of recent merging) and strong, central H_B absorption (indicative of
young stars). The core of NGC 4150 shows ubiquitous near-UV emission and
remarkable dusty substructure. Our analysis shows this galaxy to lie in the
near-UV green valley, and its pixel-by-pixel photometry exhibits a narrow range
of near-UV/optical colours that are similar to those of nearby E+A
(post-starburst) galaxies. We parametrise the properties of the recent star
formation (age, mass fraction, metallicity and internal dust content) in the
NGC 4150 pixels by comparing the observed near-UV/optical photometry to stellar
models. The typical age of the recent star formation (RSF) is around 0.9 Gyrs,
consistent with the similarity of the near-UV colours to post-starburst
systems, while the morphological structure of the young component supports the
proposed merger scenario. The RSF metallicity, representative of the
metallicity of the gas fuelling star formation, is around 0.3 - 0.5 Zsun.
Assuming that this galaxy is a merger and that the gas is sourced mainly from
the infalling companion, these metallicities plausibly indicate the gas-phase
metallicity (GPM) of the accreted satellite. Comparison to the local mass-GPM
relation suggests (crudely) that the mass of the accreted system is around
3x10^8 Msun, making NGC 4150 a 1:20 minor merger. A summation of the pixel RSF
mass fractions indicates that the RSF contributes about 2-3 percent of the
stellar mass. This work reaffirms our hypothesis that minor mergers play a
significant role in the evolution of ETGs at late epochs.Comment: 28 pages, 2 tables, accepted for publication in Ap
The role of equilibrium and disequilibrium in modeling regional growth and decline: a critical reassessment
While unable to copy/paste the abstract, the paper argues that regional differentials in wages and rents are overwhelmingly of an equilibrium nature, with disequilibrium forces having little systematic influenc
THE ROLE OF EQUILIBRIUM AND DISEQUILIBRIUM IN MODELING REGIONAL GROWTH AND DECLINE: A CRITICAL REASSESSMENT
Supermassive black holes, star formation and downsizing of elliptical galaxies
The overabundance of Mg relative to Fe, observed in the nuclei of bright
ellipticals, and its increase with galactic mass, poses a serious problem for
all current models of galaxy formation. Here we improve on the one-zone
chemical evolution models for elliptical galaxies by taking into account
positive feedback produced in the early stages of super-massive central black
hole growth. We can account for both the observed correlation and the scatter
if the observed anti-hierarchical behaviour of the AGN population couples to
galaxy assembly and results in an enhancement of the star formation efficiency
which is proportional to galactic mass. At low and intermediate galactic
masses, however, a slower mode for star formation suffices to account for the
observational properties.Comment: 7 pages, 4 figures, MNRAS accepte
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