177 research outputs found
Increased susceptibility to proactive interference in adults with dyslexia?
Recent findings show that people with dyslexia have an impairment in serial-order memory. Based on these findings, the present study aimed to test the hypothesis that people with dyslexia have difficulties dealing with proactive interference (PI) in recognition memory. A group of 25 adults with dyslexia and a group of matched controls were subjected to a 2-back recognition task, which required participants to indicate whether an item (mis)matched the item that had been presented 2 trials before. PI was elicited using lure trials in which the item matched the item in the 3-back position instead of the targeted 2-back position. Our results demonstrate that the introduction of lure trials affected 2-back recognition performance more severely in the dyslexic group than in the control group, suggesting greater difficulty in resisting PI in dyslexia.Peer reviewedFinal Accepted Versio
A Two-Field Formulation for Surfactant Transport within the Algebraic Volume of Fluid Method
Surfactant transport plays an important role in many technical processes and
industrial applications such as chemical reactors, microfluidics, printing and
coating technology. High fidelity numerical simulations of two-phase flow
phenomena reveal rich insights into the flow dynamics, heat, mass and species
transport. In the present study, a two-field formulation for surfactant
transport within the algebraic volume of fluid method is presented. The slight
diffuse nature of representing the interface in the algebraic volume of fluid
method is utilized to track the concentration of surfactant at the interface as
a volumetric concentration. Transport of insoluble and soluble surfactants is
investigated by tracking two different concentrations of the surfactant, one
within the bulk of the liquid and the other one at the interface. These two
transport equations are in turn coupled by source terms considering the
ad-/desorption processes at a liquid-gas interface. Appropriate boundary
conditions at a solid-fluid interface are formulated to ensure surfactant
conservation, while also enabling to study the ad-/desorption processes at a
solid-fluid interface. The developed numerical method is verified by comparing
the numerical simulations with well-known analytical and numerical reference
solutions. The presented numerical methodology offers a seamless integration of
surfactant transport into the algebraic volume of fluid method, where the
latter has many advantages such as volume conservation and an inherent ability
of handling large interface deformations and topological changes
Spin states of zigzag-edged Mobius graphene nanoribbons from first principles
Mobius graphene nanoribbons have only one edge topologically. How the
magnetic structures, previously associated with the two edges of zigzag-edged
flat nanoribbons or cyclic nanorings, would change for their Mobius
counterparts is an intriguing question. Using spin-polarized density functional
theory, we shed light on this question. We examine spin states of zigzag-edged
Mobius graphene nanoribbons (ZMGNRs) with different widths and lengths. We find
a triplet ground state for a Mobius cyclacene, while the corresponding
two-edged cyclacene has an open-shell singlet ground state. For wider ZMGNRs,
the total magnetization of the ground state is found to increase with the
ribbon length. For example, a quintet ground state is found for a ZMGNR. Local
magnetic moments on the edge carbon atoms form domains of majority and minor
spins along the edge. Spins at the domain boundaries are found to be
frustrated. Our findings show that the Mobius topology (i.e., only one edge)
causes ZMGNRs to favor one spin over the other, leading to a ground state with
non-zero total magnetization.Comment: 17 pages, 4 figure
Entanglement Measures for Single- and Multi-Reference Correlation Effects
Electron correlation effects are essential for an accurate ab initio
description of molecules. A quantitative a priori knowledge of the single- or
multi-reference nature of electronic structures as well as of the dominant
contributions to the correlation energy can facilitate the decision regarding
the optimum quantum chemical method of choice. We propose concepts from quantum
information theory as orbital entanglement measures that allow us to evaluate
the single- and multi-reference character of any molecular structure in a given
orbital basis set. By studying these measures we can detect possible artifacts
of small active spaces.Comment: 14 pages, 4 figure
Step-Wise Computational Synthesis of Fullerene C60 derivatives. 1.Fluorinated Fullerenes C60F2k
The reactions of fullerene C60 with atomic fluorine have been studied by
unrestricted broken spin-symmetry Hartree-Fock (UBS HF) approach implemented in
semiempirical codes based on AM1 technique. The calculations were focused on a
sequential addition of fluorine atom to the fullerene cage following indication
of the cage atom highest chemical susceptibility that is calculated at each
step. The effectively-non-paired-electron concept of the fullerene atoms
chemical susceptibility lays the foundation of the suggested computational
synthesis. The obtained results are analyzed from energetic, symmetry, and the
composition abundance viewpoints. A good fitting of the data to experimental
findings proves a creative role of the suggested synthesis methodology.Comment: 33 pages, 11 figures, 2 tables, 2 chart
Whole Genome Characterization of the Mechanisms of Daptomycin Resistance in Clinical and Laboratory Derived Isolates of Staphylococcus aureus
Background: Daptomycin remains one of our last-line anti-staphylococcal agents. This study aims to characterize the genetic evolution to daptomycin resistance in S. aureus. Methods: Whole genome sequencing was performed on a unique collection of isogenic, clinical (21 strains) and laboratory (12 strains) derived strains that had been exposed to daptomycin and developed daptomycin-nonsusceptibility. Electron microscopy (EM) and lipid membrane studies were performed on selected isolates. Results: On average, six coding region mutations were observed across the genome in the clinical daptomycin exposed strains, whereas only two mutations on average were seen in the laboratory exposed pairs. All daptomycin-nonsusceptible strains had a mutation in a phospholipid biosynthesis gene. This included mutations in the previously described mprF gene, but also in other phospholipid biosynthesis genes, including cardiolipin synthase (cls2) and CDP-diacylglycerol-glycerol-3-phosphate 3-phosphatidyltransferase (pgsA). EM and lipid membrane composition analyses on two clinical pairs showed that the daptomycin-nonsusceptible strains had a thicker cell wall and an increase in membrane lysyl-phosphatidylglycerol. Conclusion: Point mutations in genes coding for membrane phospholipids are associated with the development of reduced susceptibility to daptomycin in S. aureus. Mutations in cls2 and pgsA appear to be new genetic mechanisms affecting daptomycin susceptibility in S. aureus
Photoinduced Structural Phase Transitions in Polyacene
There exist two types of structural instability in polyacene: double bonds in
a cis pattern and those in a trans pattern. They are isoenergetic but
spectroscopically distinct. We demonstrate optical characterization and
manipulation of Peierls-distorted polyacene employing both correlated and
uncorrelated Hamiltonians. We clarify the phase boundaries of the cis- and
trans-distorted isomers, elucidate their optical-conductivity spectra, and then
explore their photoresponses. There occurs a photoinduced transformation in the
polyacene structure, but it is one-way switching: The trans configuration is
well convertible into the cis one, whereas the reverse conversion is much less
feasible. Even the weakest light irradiation can cause a transition of
uncorrelated electrons, while correlated electrons have a transition threshold
against light irradiation.Comment: 14 pages with 15 figures embedde
A study of a mutant elongation factor properties of E. coli HAK88 and its mutant elongation factor Tu
The E. coli chromosome contains two genes for elongation factor Tu, tufA (near the fusidic acid resistance marker) and tufB (near the rifampicin resistance marker). It has been discovered that the mutant E. coli K12 strain HAK88 bears a mutation in the tufB gene, which leads to the synthesis of a protein of increased acidity. To determine whether the mutation has altered the protein's function in peptide chain elongation, we have compared the reactivities of normal tufA EF-Tu and mutant tufB EF-Tu (purified together from HAK88) with the components of the AA-tRNA binding cycle. Normal tufA EF-Tu and mutant tufB EF-Tu are indistinguishable in their affinities for GDP, EF-Ts, and phe-tRNA, and differ only slightly in their affinities for ribosomes. Coupled with the results of a separate study showing the similarity of the normal tufA and tufB gene products, these experiments demonstrate that the mutation has not altered the function of tufB EF-Tu in peptide chain elongation. Contrary to the original report (Kuwano et al., 1974; J. Mol. Biol. 86 , 689–698) the HAK88 strains we have examined no longer possess a temperature-sensitive EF-Ts. The growth rates of HAK88 strains resemble the parent HAK8 strain in their lack of tRNA dependence but unlike HAK8 show varying degrees of temperature sensitivity. We conclude that HAK88 contains a physically altered but functionally intact tufB EF-Tu. The mutation in tufB should be valuable for studying in vivo the control of expression of the genes for EF-Tu.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47543/1/438_2004_Article_BF00401747.pd
Nascentome Analysis Uncovers Futile Protein Synthesis in Escherichia coli
Although co-translational biological processes attract much attention, no general and easy method has been available to detect cellular nascent polypeptide chains, which we propose to call collectively a “nascentome.” We developed a method to selectively detect polypeptide portions of cellular polypeptidyl-tRNAs and used it to study the generality of the quality control reactions that rescue dead-end translation complexes. To detect nascent polypeptides, having their growing ends covalently attached to a tRNA, cellular extracts are separated by SDS-PAGE in two dimensions, first with the peptidyl-tRNA ester bonds preserved and subsequently after their in-gel cleavage. Pulse-labeled nascent polypeptides of Escherichia coli form a characteristic line below the main diagonal line, because each of them had contained a tRNA of nearly uniform size in the first-dimension electrophoresis but not in the second-dimension. The detection of nascent polypeptides, separately from any translation-completed polypeptides or degradation products thereof, allows us to follow their fates to gain deeper insights into protein biogenesis and quality control pathways. It was revealed that polypeptidyl-tRNAs were significantly stabilized in E. coli upon dysfunction of the tmRNA-ArfA ribosome-rescuing system, whose function had only been studied previously using model constructs. Our results suggest that E. coli cells are intrinsically producing aberrant translation products, which are normally eliminated by the ribosome-rescuing mechanisms
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