Intestinal Beta-carotene absorption and cleavage in men: response of Beta-carotene and retinyl esters in the triglyceride-rich lipoprotein fraction after a single oral dose of Beta-carotene 1-3

Postprandial response curves of β-carotene and retinyl esters in a triglyceride-rich lipoprotein (TRL) fraction were evaluated as a potential measure of β-carotene uptake and cleavage. β-Carotene, retinyl ester, and triglyceride concentrations in the TRI, fraction (density < 1.006 kg/L) and plasma were measured in 10 men for 8 or 16 h after an oral dose of 15 mg β- carotene. The β-carotene response, unlike the triglyceride and retinyl ester response, can be evaluated in the TRL fraction but not in plasma. Intraindividual variations in the triglyceride-adjusted response of β- carotene and retinyl palmitate in TRL fractions were 23% and 20% and interindividual variations were 42% and 36%, respectively. A low β-carotene response was associated with a high ratio between retinyl palmitate and β- carotene responses (r = -0.56, P = 0.013). In conclusion, the measurement of β-carotene and retinyl esters in the TRL fraction after a dose of β- carotene with a vitamin A-free meal may be an appropriate method to study β- carotene uptake and cleavag

The Twitter parliamentarian database: Analyzing Twitter politics across 26 countries

This article introduces the Twitter Parliamentarian Database (TPD), a multi-source and manually validated database of parliamentarians on Twitter. The TPD includes parliamentarians from all European Free Trade Association countries where over 45% of parliamentarians are on Twitter as well as a selection of English-speaking countries. The database is designed to move beyond the one-off nature of most Twitter-based research and in the direction of systematic and rigorous comparative and transnational analysis. The TPD incorporates, in addition to data collected through Twitter\u27s streaming API and governmental websites, data from the Manifesto Project Database; the Electoral System Design Database; the ParlGov database; and the Chapel Hill Expert Survey. By compiling these different data sources it becomes possible to compare different countries, political parties, political party families, and different kinds of democracies. To illustrate the opportunities for comparative and transnational analysis that the TPD opens up, we ask: What are the differences between countries in parliamentarian Twitter interactions? How do political parties differ in their use of hashtags and what is their common ground? What is the structure of interaction between parliamentarians in the transnational debate? Alongside some interesting similarities, we find striking cross-party and particularly cross-national differences in how parliamentarians engage in politics on the social media platform

Interactions between adsorbed macromolecules : measurements on emulsions and liquid films

The aim of this study was to gain more insight into the factors, determining the inter- and intramolecular interactions between adsorbed macromolecules. To that end several experimental and theoretical approaches were followed, using well-defined systems. It was shown that these interactions could conveniently be studied by measurements on emulsions and thin free liquid films. Two different macromolecules were used: a nonionic one: polyvinyl alcohol (PVA) and an ionic one: a copolymer of methacrylic acid and the methyl ester of methacrylic acid (PMA-pe) in the molar ratio 2:1.The characterization of the used materials has been described in chapter 2. The conformational transition, occurring in dissolved polymethacrylates was briefly discussed. At low pH, the molecules occur in a compact form, the hypercoiled form, or a-conformation. At pH above ~ 6 the molecules occur in the common. more extended b-conformation. From viscometry on PVA solutions conformational parameters, such as the root mean square end-to-end distance, the length of a statistical chain element and the linear expansion factor were determined. These conformational parameters were determined in a I M aqueous glycerol solution because in the film experiments 1 M glycerol was present in the PVA solutions in order to lower the water vapour pressure.In chapter 3 the experimental methods have been described. In the first part attention was paid to the preparation of the emulsions and to the determination of basic properties, such as specific area and adsorbed amount. A variety of rheological measurements were described in the second part. A more detailed description was given of the apparatus for the dynamic measurements (the rheometer) and of that for creep measurements.The end of chapter 3 deals with the thickness measurements of polymerstabilized free liquid films. First, a description of the apparatus and the experimental procedure was given. Subsequently, a discussion followed of the calculation of thicknesses from the intensity of the reflected light. It was shown that, for the calculation of the correction to be applied to the equivalent aqueous solution thickness, the smeared out adsorbed polymer segment layers may be formally replaced by a block distribution.The inter- and intramolecular interactions between the PMA-pe segments and the effect of these interactions on the conformation of the polyelectrolyte molecule and on the rheological properties of emulsions stabilized by this polyelectrolyte, have been discussed in chapter 4. As possible attractive forces responsible for the compact conformation at low pH, VAN DER WAALS attraction and hydrophobic bonding between the methyl groups in the main chain were considered. In addition, the strength of the COULOMBIC interaction between the carboxyl groups also plays a role in the conformational transition.The conformational transition from the a- to the b-conformation in free and adsorbed PMA-pe, was studied by potentiometric titration. Data for adsorbed PMA-pe were obtained by titrating polyelectrolyte-covered emulsion droplets. It was found that the conformational transition also occurs in adsorbed PMA-pe. This conformational transition is reflected in the rheological properties of paraffin in water emulsions, stabilized by PMA-pe. It could be concluded both from viscosity and dynamic data, that strong attraction between the emulsion droplets occurs only at a low degree of neutralization α, that is, if a substantial part of the adsorbed PMA-pe is in the a-conformation. Then both the dynamic moduli and the viscosities are very high. On the contrary at high a the emulsions were very fluid with little or no indication of attraction between the adsorbed polyelectrolyte sheets.The main conclusions from the potentiometric titration data and the rheological measurements are:a. the attraction between the polyelectrolyte segments, observed at low αin solution occurs also between loops and/or tails, adsorbed on one emulsion droplet;b. the high values of the dynamic moduli and of the viscosities at low αare due to attraction between extending loops and/or tails, adsorbed on different droplets;c. the two types of interaction are very similar.This conclusion was confirmed by the influence of methanol on Na-PMA-pe stabilized emulsions and the effect of temperature. Moreover, from these experiments it could also be concluded, that probably the hyper-coiled conformation at low α, is to a large extent due to hydrophobic bonding.The influence of Ca ++ ions on the properties of the polyelectrolyte was also investigated. Potentiometric titration showed that, in the presence of Ca ++ ions, the conformational transition is moved to higher a. Again the transition is reflected in the rheological properties of emulsions, stabilized by Ca-PMA-pe. The balance between the inter- and intramolecular interaction forces and the interactions themselves are more complicated than in the case of Na-PMA-pe. This complex character is reflected in the more complex rheological functionalities (η(α), G' (α) curves) of emulsions stabilized by Ca-PMA-pe.The interactions between adsorbed macromolecules were further investigated by studying the properties of polymer stabilized thin free liquid films. Measurements on films, stabilized by PVA or PMA-pe, were reported in chapter 5.The interaction forces which must be taken into account in a PVA film are VAN DER WAALS attraction, hydrostatic pressure and steric interaction. The VAN DER WAALS attraction over a film can be calculated. The equilibrium film thicknesses of the films were determined at varying hydrostatic pressure. Then the steric repulsion force Fs between the two adsorbed PVA layers was obtained by equalizing - Fs with the hydrostatic pressure and the VAN DER WAALS attraction. So the steric repulsion force could be calculated for different equilibrium thicknesses. Next the free energy of steric interaction was found by graphic integration of the force-distance curve. These values can be compared with theoretical predictions.In order to calculate the free energy of steric interaction theoretically, a model of the segment density distribution had to be developed. The proposed semiquantitative model was based on the consideration that the molecular weight distribution of the used PVA samples is wide and the presumption that a large fraction of the segments is adsorbed as tails. Indications for this presumption were found by comparing the extrapolated ( Fs - 0) film thickness with the ellipsometric thickness of an adsorbed layer. This model leads to the conclusion, that the properties of the outer part of the adsorbed layers are dominated by a few extending tails. The free energy of steric repulsion, thus calculated with the HESSELINK et al. (1971b) theory of steric repulsion, between two adsorbed PVA ( M v = 27,000 or 86,000) layers, agrees well with the experimentally determined values for reasonable lengths of the tails.In chapter 5 also the drainage behaviour and the equilibrium thicknesses of PMA-pe films, made at different values of the degree of neutralization a, were discussed. The measured equilibrium thicknesses correlated well with ellipsometric measurements of an adsorbed layer. The drainage pattern changes if or is varied. At low αthe films are rigid, whereas at high αthey are mobile. Also the dilatational modulus decreased from α= 0.1 to α= 1.0. Probably the interaction forces between the polyelectrolyte segments which are responsible for these phenomena, are the same as those which induce the conformational transition in the molecule or which are responsible for the drastic changes in the rheological properties of emulsions stabilized by PMA-pe if αis varied.A more elaborate discussion of the rheological properties of PMA-pe stabilized emulsions is given in chapter 6. Both dynamic and creep measurements were reported.In the dynamic experiments the storage modulus G' and the loss modulus G'' were measured as a function of the frequency ω. The degree of neutralization, the polyelectrolyte supply and the salt concentration were variables. By comparing the gel point concentration of free PMA-pe with the polyelectrolyte concentration in the layer between two emulsion droplets, it was concluded that there also a gel could be formed if attractive forces between the polyelectrolyte segments dominate. This conclusion is supported by analyses of the G' (ω) and G'' (ω) curves. In cases where such a kind of gel is formed, it is possible to relate G' to the number of polyelectrolyte cross-links between two droplets. Equations were given for the case of an ideal network model and for an aggregate model of the emulsion structure. For both models equations were also derived relating G' to the VAN DER WAALS attraction between the droplets. It was found that the ideal network model was good enough to interpret semiquantitatively the results obtained for the viscoelastic emulsions. The VAN DER WAALS attraction between the emulsion droplets proved to be much less important than the interactions between the polyelectrolyte sheets. It was calculated that at αPMA-pe = 0.1, about 400-1000 polyelectrolyte bonds were formed between two emulsion droplets at interparticle distances of 30 to 50 nm. It implies that about 10-20% of the polyelectrolyte molecules, present in the contact region between two emulsion droplets, are directly involved in the formation of these bonds.A short discussion was given of the unusually high values of the loss factor tg δ. The suggestion was put forward that these high values follow from the fact that liquid must move in and out of the micro gels between adjacent emulsion droplets or from the relaxation of the polyelectrolyte cross-links, during a deformation cycle.The creep curves were analysed by assuming the existence of both strong and weak bonds between the emulsion droplets. If measured under the proper conditions the weaker (secondary) bonds are broken, but the stronger (primary) bonds are not. Then it is possible to calculate from a non-linearity in the deformation as a function of the shear stress, if any, the contribution of the secondary bonds to the shear stress. The secondary bonds were identified as VAN DER WAALS attraction between the emulsion droplets and the primary bonds as interactions between polyelectrolyte molecules adsorbed on different droplets. Again it was found that the VAN DER WAALS attraction is relatively unimportant. From the found contribution to the shear modulus of an emulsion due to VAN DER WAALS attraction and steric repulsion between the droplets the interparticle distance was calculated to be 25-30 nm. This value was of the same order of magnitude as the results of the film thickness measurements. A semiquantitative assessment of the activation energy necessary to break a polyelectrolyte-polyelectrolyte bond showed that the interactions between the methyl groups must have a cooperative character.It was concluded that the results of creep and dynamic measurements support each other.In conclusion, this study shows that both rheological measurements of sterically stabilized dispersions and the investigation of polymer stabilized thin liquid films are excellent tools for investigating the interactions between adsorbed macromolecules. Intramolecular interactions and interactions between macromolecules adsorbed on different interfaces are very similar. The latter interactions are dominated by the outer part of the adsorbed macromolecule layers.<p/

Anomalous crossover between thermal and shot noise in macroscopic diffusive conductors

We predict the existence of an anomalous crossover between thermal and shot noise in macroscopic diffusive conductors. We first show that, besides thermal noise, these systems may also exhibit shot noise due to fluctuations of the total number of carriers in the system. Then we show that at increasing currents the crossover between the two noise behaviors is anomalous, in the sense that the low frequency current spectral density displays a region with a superlinear dependence on the current up to a cubic law. The anomaly is due to the non-trivial coupling in the presence of the long range Coulomb interaction among the three time scales relevant to the phenomenon, namely, diffusion, transit and dielectric relaxation time.Comment: 4 pages, 2 figure

Point defect concentrations in metastable Fe-C alloys

Point defect species and concentrations in metastable Fe-C alloys are determined using density functional theory and a constrained free-energy functional. Carbon interstitials dominate unless iron vacancies are in significant excess, whereas excess carbon causes greatly enhances vacancy concentration. Our predictions are amenable to experimental verification; they provide a baseline for rationalizing complex microstructures known in hardened and tempered steels, and by extension other technological materials created by or subjected to extreme environments

Enhancement of quasiparticle recombination in Ta and Al superconductors by implantation of magnetic and nonmagnetic atoms

The quasiparticle recombination time in superconducting films, consisting of the standard electron-phonon interaction and a yet to be identified low temperature process, is studied for different densities of magnetic and nonmagnetic atoms. For both Ta and Al, implanted with Mn, Ta and Al, we observe an increase of the recombination rate. We conclude that the enhancement of recombination is not due to the magnetic moment, but arises from an enhancement of disorder.Comment: 4 pages, 4 figure

Channeling Effects in Direct Dark Matter Detectors

The channeling of the ion recoiling after a collision with a WIMP changes the ionization signal in direct detection experiments, producing a larger signal than otherwise expected. We give estimates of the fraction of channeled recoiling ions in NaI (Tl), Si and Ge crystals using analytic models produced since the 1960's and 70's to describe channeling and blocking effects. We find that the channeling fraction of recoiling lattice nuclei is smaller than that of ions that are injected into the crystal and that it is strongly temperature dependent.Comment: 8 pages, 12 figures, To appear in the Proceedings of the sixth International Workshop on the Dark Side of the Universe (DSU2010) Leon, Guanajuato, Mexico 1-6 June 201