2,663 research outputs found
Phase separation phenomena in solutions of cellulose acetate. I. Differential scanning calorimetry of cellulose acetate in mixtures of dioxane and water
The nature and kinetics of phase separation processes of solutions of cellulose acetate (degree of substitution, 2.5) in mixtures of dioxane and water are studied by differential scanning calorimetry (DSC). The thermograms on heating show small endothermic effects, detectable only after prolonged aging below the phase separation temperature. Experiments in two regions of the ternary diagram are of interest for the description of the formation mechanism of asymmetric membranes viz., (1) at high polymer and high concentrations and low concentrations of nonsolvent (gelation); (2) at lower polymer concentrations of nonsolvent (liquid-liquid separation followed by gelation). Endothermic effects after prolonged aging are found at high polymer concentrations (40%). These results demonstrate that gelation is very slow in these systems. At lower concentrations of polymer and high concentrations of nonsolvent (up to 40%) a more rapid type of phase separation can be observed visually on cooling. The temperature where turbidity sets in (the cloud point) is independent of the rate of cooling. In DSC experiments no exothermic effect is found on cooling. Again, after aging an endothermic effect is present. The endothermic peak, which is situated below the cloud point, is probably a result of melting of the gelled concentrated phase
Farrowing accommodation for organic pigs
Newborn piglets in organic farrowing pens have a lower survival rate than in conventional farrowing pens. This difference is mainly caused by housing the sow loose compared to crated and by climatic effects of the outdoor temperature. Organic lactating sows should have at least 7.5 m² indoor area with straw and a 2.5 m² outdoor run.
The aim of the project was to increase piglet survival in order to improve animal welfare as well as the profitability of organic farms.
In the experiment we compared survival and behaviour in 3 pen types: type 1 with outdoor run, type 2 with an indoor run and a higher proportion of solid floor and type 3 without run. Data was analysed with Analysis of Variance using parity and liveborn piglets as covariables. Results of 131 litters in total showed 9.6a, 10.8b and 9.4a (p=0.05) weaned piglets per litter for pen type 1, 2 and 3. Fouling scores indicating dunging behaviour in the indoor lying area showed 13a, 21b and 19b (p=0.04) for pen types 1, 2 and 3. We found a tendency that litters with high survival rates used the separate piglet nest sooner for lying than the litters with low survival rates. Climatic conditions seemed to be crucial for the vitality and survival of the newborn piglets.
The better climatic conditions combined with the higher proportion of solid floor resulted in a higher survival rate of the piglets. These results are currently used in a second experiment focussing on extra heating around farrowing and solid floor proportion in a new farrowing accommodation
Galactic structure towards the Open Clusters NGC 188 and NGC 3680
We present the first comparisons of a newly developed Galactic Structure and
Kinematic Model to magnitude and color counts, as well as relative proper
motions, in the fields of the open clusters NGC 188 [(l, b)= (122.8 deg, +22.4
deg)] and NGC 3680 [(l,b)= (286.8 deg, +16.9 deg)]. In addition to determining
the reddening toward these two clusters, it is shown that starcounts at
intermediate Galactic latitudes in the range 11< V< 17 allow us to constrain
the model scale-height for disk subgiants. We obtain a mean value of 250 +/- 32
pc, in agreement with previous determinations of the scale-height for
red-giants. We are also able to constrain the scale-height of main-sequence
stars, and the distance of the sun from the Galactic plane, ruling out the
possibility of a value of +40 pc, in favor of a smaller value. Comparisons with
the observed proper-motion histograms indicate that the velocity dispersion of
disk main-sequence stars must increase with distance from the Galactic plane in
order to match the observed proper-motion dispersion. The required increase is
consistent with the values predicted by dynamical models, and provides a clear
observational evidence in favor of such gradients. The shape of the observed
proper-motion distribution is well fitted within the Poisson uncertainties.
This implies that corrections to absolute proper motion (and, therefore, space
velocities) for open clusters may be obtained using our model when no inertial
reference frame is available. Using this approach, the derived tangential
motions for NGC 188 and NGC 3680 are presented.Comment: Tex type, 29 pages, 9 postscript figures. Accepted for publication in
The Astronomical Journa
Polymers in mixed solvents: feasibility of computing binary and ternary interaction parameters from intrinsic viscosities only
Characterisation of an Electrostatic Vibration Harvester
Harvesting energy from ambient vibration is proposed as an alternative to
storage based power supplies for autonomous systems. The system presented
converts the mechanical energy of a vibration into electrical energy by means
of a variable capacitor, which is polarized by an electret. A lumped element
model is used to study the generator and design a prototype. The device has
been micromachined in silicon, based on a two-wafer process. The prototype was
successfully tested, both using an external polarization source and an
electret.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/EDA-Publishing
Thermoreversible gelation of cellulose acetate solutions studied by differential scanning calorimetry
Thermoreversible gels of cellulose acetate can be obtained by cooling concentrated cellulose acetate solutions in solvent-nonsolvent mixtures of dioxane and water. Upon heating the gels, endothermic effects were observed with differential scanning calorimetry. The heat effects are ascribed to the melting of a crystalline phase consisting of cellulose triacetate units. The endothermic peaks appear only after long aging periods of up to several days. Melting points generally decrease and heats of melting increase with increasing polymer concentration and with increasing nonsolvent content. The maximum degree of crystallinity is estimated as 8%. The kinetic effects of varying the water content in the solvent mixture are discussed
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