186 research outputs found
Bacterial community adaptation to chlorinated pollutant challenge : implications for ready biodegradation testing
This study aimed to investigate the RBT outcome as a function of the bacterial inoculum during adaptation to degrade the HAs dichloroacetic acid (DCA), trichloroacetic acid (TCA) and 2-monochloropropionic acid (2MCPA). The HAs investigated were ranked, in order of greatest recalcitrance; TCA > 2MCPA > DCA. DCA degradation was associated with enrichment of a Ralstonia like phylotype and dehII expression. TCA degradation in replicate RBTs was consistently associated with a Bradyrhizobium like phylotype and dehI gene expression, regardless of the inoculum concentration used, suggesting that TCA imposes a highly selective pressure on the community. TCA degradation was affected by the inoculum concentration, as the rate of degradation was slower at the lowest inoculum concentration used, implying that TCA degradation was accomplished by cometabolism. 2MCPA was associated with various Alpha-, Beta- and Gammaproteobacteria, and the presence and expression of both dehI and dehII genes. Biodegradation of 2MCPA was strongly influenced by inoculum concentration. At lower inoculum concentrations, 2MCPA was commonly associated with a biphasic dechlorination curve, which has not been reported previously. Biphasic dechlorination curves were attributed to the enrichment of an initial degrading organism, always associated with dehII expression, which was succeeded following 50% dechlorination by a second organism, in association with dehI expression, which were supposed to act sequentially on the L- and D-2MCPA isomers, respectively. The delayed enrichment of a dehI containing organism was attributed to their low environmental abundance, relative to dehII containing organisms. This study highlights the utility of cultivation-independent methods to link more precisely community structure and function during adaptation to degrade xenobiotic compounds.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Bacterial community adaptation to chlorinated pollutant challenge: implications for ready biodegradation testing.
This study aimed to investigate the RBT outcome as a function of the bacterial inoculum during adaptation to degrade the HAs dichloroacetic acid (DCA), trichloroacetic acid (TCA) and 2-monochloropropionic acid (2MCPA). The HAs investigated were ranked, in order of greatest recalcitrance; TCA > 2MCPA > DCA. DCA degradation was associated with enrichment of a Ralstonia like phylotype and dehII expression. TCA degradation in replicate RBTs was consistently associated with a Bradyrhizobium like phylotype and dehI gene expression, regardless of the inoculum concentration used, suggesting that TCA imposes a highly selective pressure on the community. TCA degradation was affected by the inoculum concentration, as the rate of degradation was slower at the lowest inoculum concentration used, implying that TCA degradation was accomplished by cometabolism. 2MCPA was associated with various Alpha-, Beta- and Gammaproteobacteria, and the presence and expression of both dehI and dehII genes. Biodegradation of 2MCPA was strongly influenced by inoculum concentration. At lower inoculum concentrations, 2MCPA was commonly associated with a biphasic dechlorination curve, which has not been reported previously. Biphasic dechlorination curves were attributed to the enrichment of an initial degrading organism, always associated with dehII expression, which was succeeded following 50% dechlorination by a second organism, in association with dehI expression, which were supposed to act sequentially on the L- and D-2MCPA isomers, respectively. The delayed enrichment of a dehI containing organism was attributed to their low environmental abundance, relative to dehII containing organisms. This study highlights the utility of cultivation-independent methods to link more precisely community structure and function during adaptation to degrade xenobiotic compounds
Addressing the clumsiness loophole in a Leggett-Garg test of macrorealism
The rise of quantum information theory has lent new relevance to experimental
tests for non-classicality, particularly in controversial cases such as
adiabatic quantum computing superconducting circuits. The Leggett-Garg
inequality is a "Bell inequality in time" designed to indicate whether a single
quantum system behaves in a macrorealistic fashion. Unfortunately, a violation
of the inequality can only show that the system is either (i)
non-macrorealistic or (ii) macrorealistic but subjected to a measurement
technique that happens to disturb the system. The "clumsiness" loophole (ii)
provides reliable refuge for the stubborn macrorealist, who can invoke it to
brand recent experimental and theoretical work on the Leggett-Garg test
inconclusive. Here, we present a revised Leggett-Garg protocol that permits one
to conclude that a system is either (i) non-macrorealistic or (ii)
macrorealistic but with the property that two seemingly non-invasive
measurements can somehow collude and strongly disturb the system. By providing
an explicit check of the invasiveness of the measurements, the protocol
replaces the clumsiness loophole with a significantly smaller "collusion"
loophole.Comment: 7 pages, 3 figure
Effect of Salt on Phosphorylcholine-based Zwitterionic Polymer Brushes.
A quantitative investigation of the responses of surface-grown biocompatible brushes of poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) to different types of salt has been carried out using ellipsometry, quartz crystal microbalance (QCM) measurements, and friction force microscopy. Both cations and anions of varying valency over a wide range of concentrations were examined. Ellipsometry shows that the height of the brushes is largely independent of the ionic strength, confirming that the degree of swelling of the polymer is independent of the ionic character of the medium. In contrast, QCM measurements reveal significant changes in mass and dissipation to the PMPC brush layer, suggesting that ions bind to phosphorylcholine (PC) groups in PMPC molecules, which results in changes in the stiffness of the brush layer, and the binding affinity varies with salt type. Nanotribological measurements made using friction force microscopy show that the coefficient of friction decreases with increasing ionic strength for a variety of salts, supporting the conclusion drawn from QCM measurements. It is proposed that the binding of ions to the PMPC molecules does not change their hydration state, and hence the height of the surface-grown polymeric brushes. However, the balance of the intra- and intermolecular interactions is strongly dependent upon the ionic character of the medium between the hydrated chains, modulating the interactions between the zwitterionic PC pendant groups and, consequently, the stiffness of the PMPC molecules in the brush layer
Masses, Radii, and Cloud Properties of the HR 8799 Planets
The near-infrared colors of the planets directly imaged around the A star HR
8799 are much redder than most field brown dwarfs of the same effective
temperature. Previous theoretical studies of these objects have concluded that
the atmospheres of planets b, c, and d are unusually cloudy or have unusual
cloud properties. Some studies have also found that the inferred radii of some
or all of the planets disagree with expectations of standard giant planet
evolution models. Here we compare the available data to the predictions of our
own set of atmospheric and evolution models that have been extensively tested
against observations of field L and T dwarfs, including the reddest L dwarfs.
Unlike some previous studies we require mutually consistent choices for
effective temperature, gravity, cloud properties, and planetary radius. This
procedure thus yields plausible values for the masses, effective temperatures,
and cloud properties of all three planets. We find that the cloud properties of
the HR 8799 planets are not unusual but rather follow previously recognized
trends, including a gravity dependence on the temperature of the L to T
spectral transition--some reasons for which we discuss. We find the inferred
mass of planet b is highly sensitive to whether or not we include the H and K
band spectrum in our analysis. Solutions for planets c and d are consistent
with the generally accepted constraints on the age of the primary star and
orbital dynamics. We also confirm that, like in L and T dwarfs and solar system
giant planets, non-equilibrium chemistry driven by atmospheric mixing is also
important for these objects. Given the preponderance of data suggesting that
the L to T spectral type transition is gravity dependent, we present an
exploratory evolution calculation that accounts for this effect. Finally we
recompute the the bolometric luminosity of all three planets.Comment: 52 pages, 12 figures, Astrophysical Journal, in press. v2 features
minor editorial updates and correction
Nanoscale Contact Mechanics between Two Grafted Polyelectrolyte Surfaces
The adhesive and frictional behavior of end-grafted poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) films (brushes) in contact with atomic force microscope tips from which PDMAEMA or poly(methacrylic acid) (PMAA) were grafted has been shown to be a strong function of pH in aqueous solution. The interaction between the brush-coated surfaces is determined by a combination of electrostatic and noncovalent interactions, modulated by the effect of the solvation state on the brush and the resulting area of contact between the probe and the surface. For cationic PDMAEMA-PDMAEMA contacts at low pH, the brushes are highly solvated; a combination of electrostatic repulsion and a high degree of solvation (leading to a significant osmotic pressure) leads to a small area of contact, weak adhesion, and energy dissipation through plowing. As the pH increases, the electrostatic repulsion and the osmotic pressure decrease, leading to an increase in the area of contact and a concomitant increase in the strength of adhesion through hydrophobic interactions; as a consequence, the friction-load relationship becomes nonlinear as shear processes contribute to friction and the mechanics are fitted by DMT theory and, at higher pH, by the JKR model. For PDMAEMA-PMAA, the electrostatic interaction is attractive at neutral pH, leading to a large adhesion force, a large area of contact, and a nonlinear friction-load relationship. However, as the pH becomes either very small or very large, a significant charge is acquired by one of the contacting surfaces, leading to a large amount of bound solvent and a significant osmotic pressure that resists deformation. As a consequence, the area of contact is small, adhesion forces are reduced, and the friction-load relationship is linear, with energy dissipation dominated by molecular plowing
Measuring and Replicating the 1-20 µm Energy Distributions of the Coldest Brown Dwarfs::Rotating, Turbulent and Non-Adiabatic Atmospheres
Assessing the activity of microbicides against bacterial spores: knowledge and pitfalls
Bacterial endospores (spores) have a higher intrinsic resistance to microbicides as compared to other microbial forms, most likely due to their impermeable outer layers and low water content. Though structural differences between the spores of various bacterial species may account for observed variations in their resistance to microbicides, flaws in methods for testing the sporicidal activity of microbicides often exaggerate the differences. This has major implications when considering the selection of one or more surrogates to assess microbicides against clinically relevant spore-formers such as Clostridium difficile. The mounting significance of C. difficile as a pathogen is leading to a corresponding increase in the number of commercially available microbicidal formulations claiming activity against its spores without proper differentiation between the product's sporistatic and sporicidal actions. In this review we critically assess the situation and the implications of product claims on the field use of microbicidal product
Measuring and Replicating the 1-20 um Energy Distributions of the Coldest Brown Dwarfs: Rotating, Turbulent and Non-Adiabatic Atmospheres
Cold, low-mass, field brown dwarfs are important for constraining the
terminus of the stellar mass function, and also for optimizing atmospheric
studies of exoplanets. In 2020 new model grids for such objects were made
available: Sonora-Bobcat and ATMO 2020. Also, new candidate cold brown dwarfs
were announced, and new spectroscopic observations at lambda ~4.8 um were
published. In this paper we present new infrared photometry for some of the
coldest brown dwarfs, and put the new data and models together to explore the
properties of these objects. We reconfirm the importance of mixing in these
atmospheres, which leads to CO and NH_3 abundances that differ by orders of
magnitude from chemical equilibrium values. We also demonstrate that the new
models retain the known factor >~3 discrepancy with observations at 2 <~ lambda
um <~ 4, for brown dwarfs cooler than 600 K. We show that the entire 1 <~
lambda um <~ 20 energy distribution of six brown dwarfs with 260 <= T_eff K <=
475 can be well reproduced, for the first time, by model atmospheres which
include dis-equilibrium chemistry as well as a photospheric temperature
gradient which deviates from the standard radiative/convective equilibrium
value. This change to the pressure-temperature profile is not unexpected for
rotating and turbulent atmospheres which are subject to diabatic processes. A
limited grid of modified-adiabat model colors is generated, and used to
estimate temperatures and metallicities for the currently known Y dwarfs. A
compilation of the photometric data used here is given in the Appendix.Comment: 40 pages which includes 16 Figures and 10 Tables. The Journal
publication will include data behind the Figures for Figures 5, 8 and 9, and
a machine readable version of Table 1
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