24,008 research outputs found
Small-Amplitude Backbone Motions of the Spin-Labeled Lipopeptide Trichogin GA IV in a Lipid Membrane As Revealed by Electron Spin Echo
No full textTrichogin GA IV is a lipopeptide antibiotic of fungal origin, which is known to be able to modify the membrane
permeability. TOAC nitroxide spin-labeled analogues of this membrane active peptide were investigated in
hydrated bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) by electron spin echo (ESE)
spectroscopy. Because the TOAC nitroxide spin label is rigidly attached to the peptide backbone, it may
report on the backbone orientational dynamics. The ESE signal in this system is observed below ∼150 K.
Previously, three-pulse stimulated ESE was found to be sensitive to two types of orientational motion of
spin-labeled POPC lipid bilayers at these temperatures. The first type is fast stochastic librations, with a
correlation time on the nanosecond scale (which also manifests itself in a two-pulse primary ESE experiment).
The second type is slow millisecond inertial rotations. In the present work, we find that at low molar peptide
to lipid ratio (1:200), where the individual peptide molecules are randomly distributed at the membrane surface,
the spin labels show only a fast type of motion. At the high molar peptide to lipid ratio (1:20), a slow motion
is also observed. Because at this high concentration trichogin GA IV is known to change its orientation from
the in-plane topology to the transmembrane disposition, the observed onset of a slow motion may be safely
attributed to the dynamics of peptides, which are elongated along the lipid molecules of the membrane. The
possible interrelation between this backbone rotational motion of the peptide antibiotic and the membrane
leakage is discussed
The construction of Karen Karnak: The multi-author-function
No full textThis thesis is situated within the comparatively recent developments of Web 2.0 and the emergence of interactive WikiMedia, and explores the mode of authorship within a Read/Write culture compared to that of a Read/Only tradition. The hypothesis of this study is that the role of the audience has become merged with the author, and as such, represents new functions and attributes, distinct from a more conventional concept of authorship, in which the roles of audience and author are more separate. Read/Write and participatory culture, as defined by this study, is focused on collaboration, and includes the influences of D.I.Y. culture, Open-Source practices and the production of text by multiple authors. Multi-authorship presents a re-thinking of several concepts which support the notion of the individual author, since the focus of multi-authorship is not on attribution and ownership of a finished text, but on the continued malleability of a text. Modes of multi-authorship, demonstrated in the use of the pseudonyms Alan Smithee and Karen Eliot, represent declarative authors whose names signify multiple origins, whilst concurrently indicating a distinct body of work. The function of these names form an important context to this study, since primary research involves the construction of an experimental mode of multi-authorship utilising WikiMedia technology and the interaction of thirty nine participants, who are invited to create a body of work under the collective pseudonym Karen Karnak. The data generated by this experiment is analysed using aspects of Michel Foucault's author-function to identify and determine power structures inherent in the WikiMedia context. The interplay of power structures, including concepts such as identity, ownership and the body of work, affect the resulting mode of authorship and contribute to the construction of Karen Karnak, suggesting further areas of research into the emerging multi-author
Alamethicin Topology in Phospholipid Membranes by Oriented Solid-state NMR and EPR Spectroscopies: a Comparison
No full textAlamethicin, a hydrophobic peptide that is considered a paradigm for membrane channel formation, was uniformly labeled with (15)N, reconstituted into oriented phosphatidylcholine bilayers at concentrations of I or 5 mol %, and investigated by solid-state NMR spectroscopy as a function of temperature. Whereas the peptide adopts a transmembrane alignment in POPC bilayers at all temperatures investigated, it switches from a transmembrane to an in-plane orientation in DPPC membranes when passing the phase transition temperature. This behavior can be explained by an increase in membrane hydrophobic thickness and the resulting, hydrophobic mismatch condition. Having established the membrane topology of alamethicin at temperatures above and below the phase transition, ESEEM EPR was used to investigate the water accessibility of alamethicin synthetic analogues carrying the electron spin label TOAC residue at one of positions 1, 8, or 16. Whereas in the transmembrane alignment the labels at positions 8 and 16 are screened from the water phase, this is only the case for the latter position when adopting an orientation parallel to the surface. By comparing the EPR and solid-state NMR data of membrane-associated alamethicin it becomes obvious that the TOAC spin labels and the cryo-temperatures required for EPR spectroscopy have less of an effect on the alamethicin-POPC interactions when compared to DPPC. Finally, at P/L ratios of 1/100, spectral line broadening due to spin-spin interactions and thereby peptide oligomerization within the membrane were detected for transmembrane alamethicin
Language Change and SA-OT: The case of sentential negation
No full textSimulated Annealing for Optimality Theory (SA-OT) updates Optimality Theory by adding a model of performance to a theory of linguistic competence. Our aim is to show that SA-OT can contribute to language change simulations. Performance "errors" are considered to be one of the causes of variation and change. We have chosen to model the evolution of sentential negation (SN). The descriptive background adopts Jespersen's Cycle, according to which the evolution of sentential negation follows three main stages (1. pre-verbal, 2. discontinuous, and 3. post-verbal). Therefore, we advance a novel model for SN, based on SA-OT. It reproduces the three pure and the two observed mixed stages, whereas it correctly predicts the lack of an intermediate stage between 3 and 1. The success of the approach corroborates the computational, performance-based approach to the data. Finally, we employ the iterated learning paradigm to reproduce historical changes in a "simulated corpus study". This enterprise turns out to be more difficult than one would naively believe.Appeared open access as: Computational Linguistics in the Netherlands Journal (CLIN), vol. 1 (2011), pp. 21-40, and is available at http://www.clinjournal.org/sites/default/files/Lopopolo.pdfA. Lopopolo and Biró, T., “Language Change and SA-OT. The case of sentential negation”, Computational Linguistics in the Netherlands Journal, vol. 1, pp. 21-40, 2011.Peer Reviewe
Location and aggregation of the spin-labeled peptide trichogin GA IV in a phospholipid membrane as revealed by pulsed EPR
No full textThe lipopeptaibol trichogin GA IV is a 10 amino acid-long residue and α-aminoisobutyric acid-rich antibiotic peptide of fungal origin. TOAC (2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid) spin-labeled analogs of this membrane active peptide were investigated in hydrated bilayers of dipalmitoylphosphatidylcholine by electron spin echo envelope modulation (ESEEM) spectroscopy and pulsed electron-electron double resonance (PELDOR). Since, the ESEEM of the spin label appears to be strongly dependent on the presence of water molecules penetrated into the membrane, this phenomenon was used to study the location of this peptide in the membrane. This was achieved by comparing the ESEEM spectra for peptides labeled at different positions along the amino acid sequence with spectra known for lipids with spin labels at different positions along the hydrocarbon chain. To increase the ESEEM amplitude and to distinguish the hydrogen nuclei of water from lipid protons, membranes were hydrated with deuterated water. The PELDOR spectroscopy technique was chosen to study peptide aggregation and to determine the mutual distance distribution of the spin-labeled peptides in the membrane. The location of the peptide in the membrane and its aggregation state were found to be dependent on the peptide concentration. At a low peptide/lipid molar ratio (less than 1:100) the nonaggregated peptide chain of the trichogin molecules lie parallel to the membrane surface, with TOAC at the 4th residue located near the 9th–11th carbon positions of the sn-2 lipid chain. Increasing this ratio up to 1:20 leads to a change in peptide orientation, with the N-terminus of the peptide buried deeper into membrane. Under these conditions peptide aggregates are formed with a mean aggregate number of about N = 2. The aggregates are further characterized by a broad range of intermolecular distances (1.5–4 nm) between the labels at the N-terminal residues. The major population exhibits a distance of ∼2.5 nm, which is of the same order as the length of the helical peptide. We suggest that the constituting monomers of the dimer are antiparallel oriented
A Temperature-Driven, Reversible, Helical-Handedness Inversion in Peptaibol Analogues Tuned by the C-Terminal Capping Moiety
No full textThe propensity of a helical peptide to undergo thermodirected screw‐sense inversion is connected with its C‐terminal capping moiety. A C‐terminal methyl ester or carboxylic acid actively promotes the onset of a temperature‐driven screw‐sense inversion, whereas a C‐terminal amino alcohol hampers it
Stakeholder research CoVE Water SA: CoVE Water SA the umbrella for all stakeholders
No full textThe water and sanitation sector faces well-documented issues that are challenging to address, leading to the establishment of the Platform of Vocational Excellence (PoVE) Water. This platform brings together five regional Centers of Vocational Excellence (CoVE) Water in Europe and South Africa to ensure high-quality skills and competencies in the water sector. These CoVEs facilitate collaboration among stakeholders, enabling the development of vocational education and training programs to increase awareness, responsiveness to industry needs, and address sector challenges. A few months ago, CoVE Water SA was established in South Africa to achieve the previously mentioned goals. Therefore, it is important that the following research question is answered in this initial set-up phase: What actions need to be taken to enhance the effectiveness of the CoVE Water SA? To answer this research question, several important stakeholders were interviewed. Subsequently, the interviews were analysed thematically in order to extract the most important themes and quotes, PI grids were created to assess power and interest dynamics among stakeholders, and a Social Network Analysis was conducted to understand the CoVE Water SA network and potential clusters.The research findings have unveiled key aspects for enhancing the effectiveness of CoVE Water SA. The current network in the water sector has a low density, implying that many collaborations are lacking. This leads to a high degree of interdependence within the network, resulting in a non dynamic system. The lack of collaborations, such as connections with TVET colleges, schools, farmers and local communities, results in a lack of knowledge, funding and connection to the labour market. Governmental stakeholders, like DWS, EWSeta, and BGCMA, have been identified as influential players with extensive networks and important resources, Local Authorities and Research Organizations also play important roles. Universities exhibit substantial international links, making them crucial contributors. These stakeholders have the potential to provide knowledge, collaboration, and power. These are valuable insights for CoVE Water SA, fostering network growth and effectiveness in the water sector. Furthermore, six key themes have been derived from the conducted interviews, addressing the needs of stakeholders and where CoVE can make a valuable contribution. These themes include raising awareness, reducing the skills gap in the water sector, fostering international collaborations, mitigating the labour shortage in the water sector, improving education material and establishing desired collaborations. For each theme, the interviewed stakeholders have presented their views and numerous suggestions on how CoVE Water SA can assist in addressing these issues. Additionally, stakeholders have also mentioned possible failures of CoVE Water SA, which can aid in preventing any shortcomings of the platform. Furthermore, stakeholders mentioned ongoing initiatives related to the six themes, through which they can contribute to the platform. From the Thematic Analysis, PI Grids and the SNA, a set of actions have emerged that are essential for enhancing the effectiveness of CoVE Water SA. These actions revolve around expanding and enhancing the network, organising activities and contributing to educational improvement. In terms of broadening and strengthening the network, the platform should focus on enhancing the collaborations among educational groups, building stronger relations with international institutions in Europe and Africa, involving TVETs and schools within the water network, improving stakeholder involvement and encouraging the involvement of Local Communities to increase awareness and knowledge about water issues. Furthermore, CoVE Water SA should play a role in organising activities to raise awareness of Water Resource Management. Additionally, it should assist in improving curricula, supporting students’ preparation for the workforce and making the education more practical instead of only theoretical. CoVE Water SA should also provide training and learning resources as well as comprehensive courses.However, this study recognizes several limitations that should be considered in future research and when implementing recommendations for CoVE Water SA. These limitations encompass factors like a limited scope due to resource and time constraints, minimal varied interviewee responses, and potential biases in responses. Addressing these limitations will be crucial in guiding future research and actions for CoVE Water SA.CEGM3000Civil Engineerin
Interview with Erica Jolly - teacher, author and founding member of SA Social Studies Teachers Association
No full textErica is a teacher and author who was a founding member of the SA Social Studies Teachers Association (contributing to its text books) and the SA History Teachers Association. She took her Masters in English Literature at Flinders University and taught in Girls and Boys Technical Colleges for 40 years. Erica's published works include a history of vocational education in South Australia from 1897 - 2001, We Came to Marion 1955 - 1995 (1995), A Broader Vision: Voices of Vocational Education in SA (2001), Challenging the Divide: Approaches to Science and Poetry (2010), and Making a Stand (2015)
Historický vývoj a charakteristika rozvojovej pomoci
No full textV príspevku sa autor zaoberá vývojom povojnových rozvojových teórií, ktorých podstatou je skúmanie príčin, dôsledkov zaostalosti krajín rozvojového sveta a vzniku ekonomických a spoločenských disparít medzi jednotlivými regiónmi sveta. Z chronologického hľadiska sa autor v príspevku venuje relevantným historickým aspektom, ktoré ovplyvnili vznik rozvojovej pomoci vo forme ako ju poznáme v súčasnosti. Východiskovou teóriou zahraničnej rozvojovej pomoci sa stala teória „Začarovaného kruhu chudoby“ a z nej vychádzajú mnohí autori, ktorí hľadajú východiská zo zaostalosti a prehlbovania sa rozdielov medzi vyspelými a zaostalými krajinami sveta. Jednotlivé regióny sú špecifické určitými charakteristikami, ktoré autor rozoberá v poslednej časti príspevku.rozvojové teórie, rozvojová pomoc, zahraničná pomoc, začarovaný kruh
Le Dr Doyen, sa Staphylase et sa Mycolysine
No full textDer Dr Doyen, seine Staphylase und seine Mycolysine.
Der Verfasser gibt einige Auskünfte über diese zwei, von Marcel Proust erwähnte Arzneimittel, und deren Hersteller, Eugène-Louis Doyen, 1859 geboren.Dr Doyen, his Staphylase and his Mycolysine.
The author provides some information on these two medications mentioned by Marcel Proust, and on their discover, Eugène-Louis Doyen, born in 1859.Lefebvre Thierry. Le Dr Doyen, sa Staphylase et sa Mycolysine. In: Revue d'histoire de la pharmacie, 79ᵉ année, n°289, 1991. pp. 193-198
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