23,929 research outputs found
The evolution of the self-lensing binary KOI-3278: evidence of extra energy sources during CE evolution
Post-common-envelope binaries (PCEBs) have been frequently used to
observationally constrain models of close-compact-binary evolution, in
particular common-envelope (CE) evolution. However, recent surveys have
detected PCEBs consisting of a white dwarf (WD) exclusively with an M dwarf
companion. Thus, we have been essentially blind with respect to PCEBs with more
massive companions. Recently, the second PCEB consisting of a WD and a G-type
companion, the spectacularly self-lensing binary KOI-3278, has been identified.
This system is different from typical PCEBs not only because of the G-type
companion, but also because of its long orbital period. Here we investigate
whether the existence of KOI-3278 provides new observational constraints on
theories of CE evolution. We reconstruct its evolutionary history and predict
its future using BSE, clarifying the proper use of the binding energy parameter
in this code. We find that a small amount of recombination energy, or any other
source of extra energy, is required to reconstruct the evolutionary history of
KOI-3278. Using BSE we derive progenitor system parameters of M1,i = 2.450
Msun, M2,i = 1.034 Msun, and Porb,i ~ 1300 d. We also find that in ~9 Gyr the
system will go through a second CE phase leaving behind a double WD, consisting
of a C/O WD and a He WD with masses of 0.636 Msun and 0.332 Msun, respectively.
After IK Peg, KOI-3278 is the second PCEB that clearly requires an extra source
of energy, beyond that of orbital energy, to contribute to the CE ejection.
Both systems are special in that they have long orbital periods and massive
secondaries. This may also indicate that the CE efficiency increases with
secondary mass.Comment: Accepted for publication in A&A Letters, 4 pages, 2 figure
A Proton Magnetic Resonance Study of the Association of Lysozyme with Monosaccharide Inhibitors
It has been shown that the acetamido methyl protons of N-acetyl-d-glucosamine undergo a chemical shift to higher fields in their proton magnetic resonance spectrum when the inhibitor is bound to lysozyme. The observed chemical shift in the presence of the enzyme is different for the agr- and ß-anomeric forms of 2-acetamido-2-deoxy-d-glucopyranose indicating either a difference in the affinity of the anomeric forms for lysozyme or different magnetic environments for the methyl protons in their enzyme-bound state. That the agr- and ß-anomeric forms of GlcAc bind to lysozyme in a competitive fashion was indicated by observing the proton magnetic resonance spectra in the presence of 2-acetamido-d3-2-deoxy-agr-d-glucopyranose. The methyl glycosides, methyl-agr-GlcAc and methyl-ß-GlcAc, were also shown to bind competitively with both anomers of GlcAc. Quantitative analysis of the chemical shift data observed for the association of GlcAc with lysozyme was complicated by the mutarotation of GlcAc between its agr- and ß-anomeric forms. However, in the case of the methyl glucosides, where the conformation of each anomer is frozen, it was possible to analyze the chemical shift data in a straightforward manner, and the dissociation constant as well as the chemical shift of the acetamido methyl protons of the enzyme-inhibitor complex was determined for both anomers. The results indicate that the two anomers of methyl-GlcAc bind to lysozyme with slightly different affinities but that the acetamido methyl groups of both anomers experience identical magnetic environments in the enzyme-inhibitor complex
Synthesis and characterisation of Fe<sub>6</sub> and Fe<sub>12</sub> clusters using bicine
Reaction of bicine {BicH3, N,N-bis(2-hydroxyethyl)glycine} with an Fe(III) oxo-centered pivalate triangle in MeCN in the presence of Et<sub>2</sub>NH yields [Et<sub>2</sub>NH<sub>2</sub>]<sub>2</sub>[Fe<sub>6</sub>O<sub>2</sub>(OH)<sub>2</sub>(Bic)<sub>2</sub>(O<sub>2</sub>CCMe<sub>3</sub>)<sub>8</sub>], which possesses an S = 5 ground state.
Changing the base to NaOMe produces [Fe<sub>12</sub>O<sub>4</sub>(Bic)<sub>4</sub>(HBic)<sub>4</sub>(O<sub>2</sub>CCMe<sub>3</sub>)<sub>8</sub>], which contains two Fe6 units bridged by the carboxylate arms from the bicine ligands. The complex displays strong antiferromagnetic coupling leading to an S = 0 ground state
Intention and motor representation in purposive action
Are there distinct roles for intention and motor representation in explaining the purposiveness of action? Standard accounts of action assign a role to intention but are silent on motor representation. The temptation is to suppose that nothing need be said here because motor representation is either only an enabling condition for purposive action or else merely a variety of intention. This paper provides reasons for resisting that temptation. Some motor representations, like intentions, coordinate actions in virtue of representing outcomes; but, unlike intentions, motor representations cannot feature as premises or conclusions in practical reasoning. This implies that motor representation has a distinctive role in explaining the purposiveness of action. It also gives rise to a problem: were the roles of intention and motor representation entirely independent, this would impair effective action. It is therefore necessary to explain how intentions interlock with motor representations. The solution, we argue, is to recognise that the contents of intentions can be partially determined by the contents of motor representations. Understanding this content-determining relation enables better understanding how intentions relate to actions
Modelling a two-dimensional spatial distribution of mycotoxin concentration in bulk commodities to design effective and efficient sample selection strategies
Mycotoxins in agricultural commodities are a hazard to human and animal health.
Their heterogeneous spatial distribution in bulk storage or transport makes it
particularly difficult to design effective and efficient sampling plans. There
has been considerable emphasis on identifying the different sources of
uncertainty associated with mycotoxin concentration estimations, but much less
on identifying the effect of the spatial location of the sampling points. This
study used a two-dimensional statistical modelling approach to produce detailed
information on appropriate sampling strategies for surveillance of mycotoxins in
raw food commodities. The emphasis was on deoxynivalenol (DON) and ochratoxin A
(OTA) in large lots of grain in storage or bulk transport. The aim was to
simulate a range of plausible distributions of mycotoxins in grain from a set of
parameters characterising the distributions. For this purpose, a model was
developed to generate data sets which were repeatedly sampled to investigate the
effect that sampling strategy and the number of incremental samples has on
determining the statistical properties of mycotoxin concentration. Results
showed that, for most sample sizes, a regular grid proved to be more consistent
and accurate in the estimation of the mean concentration of DON, which suggests
that regular sampling strategies should be preferred to random sampling, where
possible. For both strategies, the accuracy of the estimation of the mean
concentration increased significantly up to sample sizes of 40-60 (depending on
the simulation). The effect of sample size was small when it exceeded 60 points,
which suggests that the maximum sample size required is of this order. Similar
conclusions about the sample size apply to OTA, although the difference between
regular and random sampling was small and probably negligible for most sample
sizes
Synthesis of empty bacterial microcompartments, directed organelle protein incorporation, and evidence of filament-associated organelle movement
Compartmentalization is an important process, since it allows the segregation of metabolic activities and, in the era of synthetic biology, represents an important tool by which defined microenvironments can be created for specific metabolic functions. Indeed, some bacteria make specialized proteinaceous metabolic compartments called bacterial microcompartments (BMCs) or metabolosomes. Here we demonstrate that the shell of the metabolosome (representing an empty BMC) can be produced within E. coil cells by the coordinated expression of genes encoding structural proteins. A plethora of diverse structures can be generated by changing the expression profile of these genes, including the formation of large axial filaments that interfere with septation. Fusing GFP to PduC, PduD, or PduV, none of which are shell proteins, allows regiospecific targeting of the reporter group to the empty BMC. Live cell imaging provides unexpected evidence of filament-associated BMC movement within the cell in the presence of Pdu
Self-reported pain severity is associated with a history of coronary heart disease
This study was funded by Arthritis Research UK (grant number: 17292).Peer reviewedPublisher PD
- …