276 research outputs found
Nonionic Hydrophilic Surfaces: Adsorption and Interactions
An overview is given of recent studies of nonionic, hydrophilic surfaces formed by the adsorption of surfactants or surface active polymers. Hydrophobic surfaces can be easily hydrophilized by the adsorption of nonionic surfactants or block copolymers containing hydrophobic chain segments; the cooperative interaction between the hydrocarbon moieties contributes more to the free energy of adsorption than the interaction with the hydro- phobic surface.
Hydrophilic layers are also readily formed on hydrophilic surfaces provided specific interaction between the hydrophilic end groups and the surface creates a sufficiently hydrophobic surface so that a second layer can be formed through cooperative interaction. The temperature dependence of the interaction forces between layers of surfactants can be closely correlated with their phase equilibria with water.
In order to prevent protein adsorption the surface should be neither charged nor hydrophobic; it is shown that, accordingly, protein adsorption is extremely low on polyethylene oxide-covered surfaces
GĂ„rdarnas Smaker
Historiskt sett har det varit svÄrt för smÄskaliga livsmedelsproducenter att fÄ marknadstilltrÀde. Dagligvaruhandeln har stor makt över vad som saluförs i butikerna och butikskedjorna har strÀvat mot ett fÄtal leverantörer med hög effektivitet. För att överbrygga dessa problem har en grupp smÄskaliga livsmedelsproducenter i VÀsterÄstrakten startat en ekonomisk förening vid namn GÄrdarnas Smaker.
Denna studie analyserar olika faktorer, som pĂ„verkar GĂ„rdarnas Smakers utveckling. I problemanalysen identifieras fyra faktorer, som pĂ„verkar GĂ„rdarnas Smakers grad av framgĂ„ng. Dessa faktorer Ă€r konceptets utformning, kapitalanskaffning, gratispassagerarproblem samt associationsform och styrning. JĂ€mförelser med tvĂ„ liknande koncept, Dalslandsmat och SjuhĂ€radsmat, vilka bĂ„da Ă€r ekonomiska föreningar görs. Ăven BjĂ€re Hembygd, som Ă€r ett aktiebolag, anvĂ€nds som jĂ€mförelseobjekt.
Den teoretiska bas, som anvĂ€nts för att analysera GĂ„rdarnas Smaker, Ă€r agent- och Ă€ganderĂ€ttsteorierna. Agentteorin innebĂ€r att agenten anlitas av huvudmannen för att göra nĂ„got i den senares intresse. FörutsĂ€ttningar för teorin Ă€r individuell nyttomaximering, begrĂ€nsad rationalitet, och informationsasymmetri. Grundtanken i Ă€ganderĂ€ttsteorin Ă€r att det man Ă€ger, det vĂ„rdar man. ĂganderĂ€ttsproblem kan delas in i problem med gemensam egendom, horisontproblem samt portföljproblem.
Konceptets utformning och flexibilitet Àr av stor vikt, dÄ efterfrÄgan pÄ lokalproducerade livsmedel har ökat. Dessutom har lokalproducerade livsmedel under senaste tiden fÄtt nya förutsÀttningar pÄ marknaden. Det blir dÀrmed viktigt att kunna anpassa verksamheten till omvÀrldsförÀndringar för att kunna kostnadsminimera, effektivisera samt bibehÄlla produktiviteten.
Kapitalanskaffningen i GÄrdarnas Smaker har i ett första skede skett genom en medlemsavgift pÄ 2500 kr. Ytterligare kapital tillkommer genom en serviceavgift pÄ fyra procent av försÀljningsbeloppet. Detta föranleder en lÄg kapitalnivÄ som begrÀnsar flexibiliteten vid en marknadsförÀndring, vilket medför sÄrbarhet.
Olika former av gratispassagerarproblem dels i form av delaktighet i styrningen och graden av engagemang och dels i form av kapitalnivÄn förekommer i GÄrdarna Smaker. Ett fÄtal av medlemmarna visar mycket starkt engagemang och delaktighet i styrningen av GÄrdarnas Smaker, medan de andra inte har lika stort engagemang.
Valet av associationsform var i GÄrdarnas Smakers fall tÀmligen naturligt. I en ekonomisk förening har alla medlemmar lika möjlighet att vara delaktiga i styrningen, och uppstartskostnaderna för en ekonomisk förening Àr lÄga. Styrningen av GÄrdarnas Smaker blir komplex, dÄ alla större beslut mÄste förankras i medlemskÄren, dÀr varje medlem har en röst.Historically it has been difficult for small-scale food-producers to gain market access. The
three large chains dominating the Swedish retail market have great power over what is to be
sold in the stores, and they strive for a small number of suppliers with high efficiency. To
break these problems a group of small-scale food-producers in the VÀsterÄsarea started a cooperative
firm named GĂ„rdarnas Smaker.
This study analyses different factors that affect the development of GĂ„rdarnas Smaker. Four
such factors are identified in the problem analysis. These are; design of the concept, capital
acquisition, freerider-problems and legal form along with control. Comparisons with similar
projects like Dalslandsmat and SjuhÀradsmat, which both are co-operatives, are made. BjÀre
Hembygd which is an investor owned firm is also used as comparison.
The theories used to analyse GĂ„rdarnas Smaker are the agency and property rights theories.
The agency theory implies that an agent is engaged by the principal to do something in his
interest. The presumptions of the theory are individual profit-maximisation, bounded
rationality and asymmetric information. The cornerstone in the property rights theory is that
what you own is something you take care of. Property rights problem can be divided into
problems with joint resources, horizon problems and portfolio problems.
The design of the concept and flexibility is of great importance when the demand for locallyproduced
food has increased during the last period of time, and locally produced food has got
new conditions on the market. Therefore it stresses to adapt the activities due to changes on
the market, to be able to maintain efficiency and productivity.
The capital acquisition in GĂ„rdarnas Smaker takes place by a member-fee of 2500 SEK.
Additional capital occurs by a service-fee of four percent. This leads to a low level of capital
which restricts flexibility in a change on the market, which leads to vulnerability.
Different types of freerider problems occur in GĂ„rdarnas Smaker both in terms participation
in the control and the degree of engagement and in terms of amount of capital within the cooperative.
Some of the members show very strong engagement and participation in the control
of GĂ„rdarnas Smaker, while the others donât have the same engagement.
The selection of type of association in the GĂ„rdarnas Smakerâs case was fairly simple. In a cooperative
all members have the same possibility to take part in the control, and the start-upcosts
in a co-operative are low. The control of GĂ„rdarnas Smaker turns complex when all
major decisions have to be approved by the membership, where each member has one vote
On modeling and measuring viscoelasticity with dynamic Atomic Force Microscopy
The interaction between a rapidly oscillating atomic force microscope tip and
a soft material surface is described using both elastic and viscous forces with
a moving surface model. We derive the simplest form of this model, motivating
it as a way to capture the impact dynamics of the tip and sample with an
interaction consisting of two components: interfacial or surface force, and
bulk or volumetric force. Analytic solutions to the piece-wise linear model
identify characteristic time constants, providing a physical explanation of the
hysteresis observed in the measured dynamic force quadrature curves. Numerical
simulation is used to fit the model to experimental data and excellent
agreement is found with a variety of different samples. The model parameters
form a dimensionless impact-rheology factor, giving a quantitative physical
number to characterize a viscoelastic surface that does not depend on the tip
shape or cantilever frequency.Comment: 13 pages, 7 figure
Microstructure of chemically modified wood using X-ray computed tomography in relation to wetting properties
X-ray computed tomography (XCT) was utilized to visualize and quantify the 2D and 3D microstructure of acetylated southern yellow pine (pine) and maple, as well as furfurylated pine samples. The total porosity and the porosity of different cell types, as well as cell wall thickness and maximum opening of tracheid lumens were evaluated. The wetting properties (swelling and capillary uptake) were related to these microstructural characteristics. The data show significant changes in the wood structure for furfurylated pine sapwood samples, including a change in tracheid shape and filling of tracheids by furan polymer. In contrast, no such changes were noted for the acetylated pine samples at the high resolution of 0.8 mu m. The XCT images obtained for the furfurylated maple samples demonstrated that all ray cells and some vessel elements were filled with furan polymer while the fibers largely remained unchanged. Furfurylation significantly decreased the total porosity of both the maple and pine samples. Furthermore, this was observed in both earlywood (EW) and latewood (LW) regions in the pine samples. In contrast, the total porosity of pine samples was hardly affected by acetylation. These findings are in line with wetting results demonstrating that furfurylation reduces both swelling and capillary uptake in contrast to acetylation which reduces mostly swelling. Furfurylation significantly increased the cell wall thickness of both the maple and pine samples, especially at higher levels of furfurylation
Effect of solvent quality and chain density on normal and frictional forces between electrostatically anchored thermoresponsive diblock copolymer layers
Equilibration in adsorbing polymer systems can be very slow, leading to different physical properties at a given condition depending on the pathway that was used to reach this state. Here we explore this phenomenon using a diblock copolymer consisting of a cationic anchor block and a thermoresponsive block of poly(2-isopropyl-2-oxazoline), PIPOZ. We find that at a given temperature different polymer chain densities at the silica surface are achieved depending on the previous temperature history. We explore how this affects surface and friction forces between such layers using the atomic force microscope colloidal probe technique. The surface forces are purely repulsive at temperaturesPeer reviewe
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Modeling and Measuring Viscoelasticity with Dynamic Atomic Force Microscopy
The interaction between a rapidly oscillating atomic-force-microscope tip and a soft-material surface is described with use of both elastic and viscous forces in a moving-surface model. We present the simplest form of this model, motivating our derivation with the models ability to capture the impact dynamics of the tip and sample with an interaction consisting of two components: interfacial or surface force, and bulk or volumetric force. Analytic solutions to the piecewise linear model identify characteristic time constants, providing a physical explanation for the hysteresis observed in the measured dynamic-force-quadrature curves. Numerical simulation is used to fit the model to experimental data, and excellent agreement is found with a variety of different samples. The model parameters form a dimensionless impact-rheology factor, giving a quantitative physical number to characterize a viscoelastic surface that does not depend on the tip shape or cantilever frequency
Expression of 5-lipoxygenase and 15-lipoxygenase in rheumatoid arthritis synovium and effects of intraarticular glucocorticoids
The past years have witnessed tremendous progress in the treatment of rheumatoid arthritis, a chronic debilitating autoimmune disease mainly characterized by joint inflammation with progressive tissue destruction and loss of function. This condition affects 0.5-1% of the population, is associated with important co-morbidities and represents a heavy economical burden. New strategies, employing early and aggressive therapies with classical drugs or new agents, have resulted in impressive improvements in controlling disease activity. In some cases they even lead to clinical remission. Despite potent and efficient biological agents that specifically modulate distinct pathological pathways a large proportion of patients remain unresponsive to these therapies; drug-free remission is also difficult to achieve since attempting discontinuation of treatment usually results in disease flare.
In rheumatoid arthritis joints there is a constant activation of complex networks of cytokines and factors mediating immune interactions and inflammation, in which prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) are important players and contributors to pathogenesis. Our research aimed to investigate the synovial expression of enzymes controlling prostaglandin E2 synthesis and degradation â cyclooxygenase (COX) 1 and 2, microsomal prostaglandin E2 synthase 1 (MPGES1) and 15-prostaglandin dihydrogenase (15-PGDH) as well as enzymes involved in leukotriene synthesis, such as 5-lipoxygenase (LO) and 15-LO. In addition, we evaluated how traditional and new therapies influence these pathways, by analyzing enzyme expression before and after systemic treatment with tumor necrosis factor (TNF) antagonists, rituximab or methotrexate, as well as before and after intra-articular treatment with glucocorticoids. We also evaluated the in vitro effects of TNF antagonists and glucocorticoids on synovial fluid cells and that of methotrexate on synovial fibroblasts.
We demonstrated that synovial tissue from RA patients displayed an important expression of enzymes involved in the metabolism of PGE2, as well as 5-LO and 15-LO. MPGES1 and COX-2, the inflammation-inducible enzymes co-localized mainly in fibroblasts and macrophage-like cells and accounted for the local PGE2 production. Intra-articular glucocorticoids significantly reduced all enzymes involved in the PGE2 cascade â COX-1 and COX-2, MPGES1 and 15-PGDH, but also 5-LO, responsible for leukotriene formation. However, they did not influence the expression of 15-LO, an enzyme involved in the formation of both pro-and anti-inflammatory lipid mediators. Regarding the effects of TNF blockers, rituximab or methotrexate, they did not alter the expression profile of enzymes involved in PGE2 metabolism despite showing clinical efficiency in improving disease activity. Although anti-TNF agents reduced the in vitro expression of MPGES1 and COX-2 in synovial fluid cells, the lack of effect ex vivo in biopsies emphasized once again the differences between synovial compartments and possibly the difficulty in mimicking the micro-environment at the site of inflammation in vitro.
In conclusion, this thesis demonstrates that potent anti-rheumatic drugs currently used in the clinic with good efficiency also leave inflammatory pathways un-affected, which may account for subclinical ongoing disease activity. Blocking the PGE2 pathway by using MPGES1 inhibitors as combination therapy may show benefit in dampening ongoing local inflammation
Polymersomes at the solid-liquid interface:Dynamic morphological transformation and lubrication
Polymersomes are hollow spheres self-assembled from amphiphilic block copolymers of certain molecular architecture. Whilst they have been widely studied for biomedical applications, relatively few studies have reported their interfacial properties. In particular, lubrication by polymersomes has not been previously reported. Here, interfacial properties of polymersomes self-assembled from poly(butadiene)-poly(ethylene oxide) (PBD-PEO; molecular weight 10,400 g molâ1) have been studied at both hydrophilic and hydrophobic surfaces. Their morphology at silica and mica surfaces was imaged with quantitative nanomechanical property mapping atomic force microscopy (QNM AFM), and friction and surface forces they mediate under confinement between two surfaces were studied using colloidal probe AFM (CP-AFM). We find that the polymersomes remained intact but adopted flattened conformation once adsorbed to mica, with a relatively low coverage. However, on silica these polymersomes were unstable, rupturing to form donut shaped residues or patchy bilayers. On a silica surface hydrophobized with a 19 nm polystyrene (PS) film, the polymer vesicles formed a more stable layer with a higher surface coverage as compared to the hydrophilic surface, and the interfacial structure also evolved over time. Moreover, friction was greatly reduced on hydrophobized silica surfaces in the presence of polymersomes, suggesting their potential as effective aqueous lubricants.</p
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