342 research outputs found
Rheology of protein-stabilised emulsion gels envisioned as composite networks. 1 - Comparison of pure droplet gels and protein gels
Protein-stabilised emulsion gels can be studied in the theoretical framework
of colloidal gels, because both protein assemblies and droplets may be
considered as soft colloids. These particles differ in their nature, size and
softness, and these differences may have an influence on the rheological
properties of the gels they form. Pure gels made of milk proteins (sodium
caseinate), or of sub-micron protein-stabilised droplets, were prepared by slow
acidification of suspensions at various concentrations. Their microstructure
was characterised, their viscoelasticity, both in the linear and non-linear
regime, and their frequency dependence were measured, and the behaviour of the
two types of gels was compared. Protein gels and droplet gels were found to
have broadly similar microstructure and rheological properties when compared at
fixed volume fraction, a parameter derived from the study of the viscosity of
the suspensions formed by proteins and by droplets. The viscoelasticity
displayed a power law behaviour in concentration, as did the storage modulus in
frequency. Additionally, strain hardening was found to occur at low
concentration. These behaviours differed slightly between protein gels and
droplet gels, showing that some specific properties of the primary colloidal
particles play a role in the development of the rheological properties of the
gels.Comment: 27 pages, 6 figure
Rheology of protein-stabilised emulsion gels envisioned as composite networks. 2 - Framework for the study of emulsion gels
The aggregation of protein-stabilised emulsions leads to the formation of
emulsion gels. These soft solids are classically envisioned as droplet-filled
matrices. Here however, it is assumed that protein-coated sub-micron droplets
contribute to the network formation in a similar way to proteins. Emulsion gels
are thus envisioned as composite networks made of proteins and droplets.
Emulsion gels with a wide range of composition are prepared and their
viscoelasticity and frequency dependence are measured. Their rheological
behaviours are then analysed and compared with the properties of pure gels
presented in the first part of this study. The rheological behaviour of
emulsion gels is shown to depend mostly on the total volume fraction, while the
composition of the gel indicates its level of similarity with either pure
droplet gels or pure protein gels. These results converge to form an emerging
picture of protein-stabilised emulsion gel as intermediate between droplet and
protein gels. This justifies a posteriori the hypothesis of composite networks,
and opens the road for the formulation of emulsion gels with fine-tuned
rheology.Comment: 22 pages, 5 figure
Detection of Far-Infrared Water Vapor, Hydroxyl, and Carbon Monoxide Emissions from the Supernova Remnant 3C 391
We report the detection of shock-excited far-infrared emission of H2O, OH,
and CO from the supernova remnant 3C 391, using the ISO Long-Wavelength
Spectrometer. This is the first detection of thermal H2O and OH emission from a
supernova remnant. For two other remnants, W~28 and W~44, CO emission was
detected but OH was only detected in absorption. The observed H2O and OH
emission lines arise from levels within ~400 K of the ground state, consistent
with collisional excitation in warm, dense gas created after the passage of the
shock front through the dense clumps in the pre-shock cloud. The post-shock gas
we observe has a density ~2x10^5 cm^{-3} and temperature 100-1000 K, and the
relative abundances of CO:OH:H2O in the emitting region are 100:1:7 for a
temperature of 200 K. The presence of a significant column of warm H2O suggests
that the chemistry has been significantly changed by the shock. The existence
of significant column densities of both OH and H2O, which is at odds with
models for non-dissociative shocks into dense gas, could be due to
photodissociation of H2O or a mix of fast and slow shocks through regions with
different pre-shock density.Comment: AASTeX manuscript and 4 postscript figure
A crystal plasticity study of the micromechanics of interfaces in TiAl
Submicron resolution deformation mapping techniques implemented into both micro and macro mechanical testing have recently provided measurements of the deformation of titanium aluminide at the microstructural scale. Experimental observations indicate that damage in such alloy strongly depends on the way shear localization associated with slip bands or twins is accommodated at the interface between colonies. Here, crystal plasticity finite element analysis has been carried out to simulate the relevant micromechanics. It is shown that it is possible to capture the deformation patterns observed at colony boundaries, therefore providing trustworthy predictions of the associated stress field. Different conditions are explored for which a given imposed deformation can be achieved with minimum stress concentration. The implications for microstructure engineering aimed to delay the nucleation of damage in such alloy are discussed
Using coupled micropillar compression and micro-Laue diffraction to investigate deformation mechanisms in a complex metallic alloy Al13Co4
In this investigation, we have used in-situ micro-Laue diffraction combined with micropillar compression of focused ion beam milled Al13Co4 complex metallic alloy to study the evolution of deformation in Al13Co4. Streaking of the Laue spots showed that the onset of plastic flow occured at stresses as low as 0.8 GPa, although macroscopic yield only becomes apparent at 2 GPa. The measured misorientations, obtained from peak splitting, enabled the geometrically necessary dislocation density to be estimated as 1.1 x 1013 m-2
LESSONS FROM THE MOTORIZED MIGRATIONS
Ten experiments have been conducted to determine if cranes can be led on migration and if those so trained will repeat migrations on their own. Results have been mixed as we have experienced the mishaps common to pilot studies. Nevertheless, we have learned many valuable lessons. Chief among these are that cranes can be led long distances behind motorized craft (air and ground), and those led over most or the entire route will return north come spring and south in fall to and from the general area of training. However, they will follow their own route. Groups transported south and flown at intervals along the route will migrate but often miss target termini. If certain protocol restrictions are followed, it is possible to make the trained cranes wild, however, the most practical way of so doing is to introduce them into a flock of wild cranes. We project that it is possible to create or restore wild migratory flocks of cranes by first leading small groups from chosen northern to southern termini
Viscosity of protein-stabilised emulsions:contributions of components and development of a semi-predictive model
Protein-stabilised emulsions can be seen as mixtures of unadsorbed proteins
and of protein-stabilised droplets. To identify the contributions of these two
components to the overall viscosity of sodium caseinate o/w emulsions, the
rheological behaviour of pure suspensions of proteins and droplets were
characterised, and their properties used to model the behaviour of their
mixtures. These materials are conveniently studied in the framework developed
for soft colloids. Here, the use of viscosity models for the two types of pure
suspensions facilitates the development of a semi-empirical model that relates
the viscosity of protein-stabilised emulsions to their composition.Comment: 28 pages, 11 figure
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Two alternative approaches to access mixed hydride-amido zinc complexes : synthetic, structural and solution implications
Using bis(amide) Zn(HMDS)2 (HMDS = 1,1,1,3,3,3-hexamethyldisilazide) as a precursor, this study explores the synthesis of N-heterocyclic carbene stabilized mixed amido-hydride zinc complexes using two alternative hydride sources, namely dimethylamine borane (DMAB) and phenylsilane PhSiH3. Hydride-rich zinc cluster Zn4(HMDS)2H6·2IPr (1) (IPr = 1,3-bis(2,6-di-isopropylphenyl)imidazol-2-ylidene), which can be envisaged as a co-complex of IPr·ZnH2 and (HMDS)ZnH, is obtained when DMAB is employed, with the concomitant formation of heteroleptic bis(amido)borane [HB(NMe2)(HMDS)] and H2 evolution. NMR studies in d8-THF show that although the bulky carbene IPr does not bind to the zinc bis(amide), its presence in the reaction media is required in order to stabilise 1. Reactions using the slightly less sterically demanding NHC IXy (IXy = 1,3-bis-(2,6-dimethylphenyl)imidazol-2-ylidene) led to the isolation and structural elucidation of the carbene adduct Zn(HMDS)2·IXy (2). Contrastingly, mixtures of equimolar amounts of PhSiH3 and the zinc bis(amide) (60 °C, 3 h, hexane) afforded monomeric heteroleptic hydride (HMDS)ZnH·IPr (3). NMR studies, including DOSY experiments, revealed that while the integrity of 3 is retained in polar d8-THF solutions, in lower polarity C6D6 it displays a much more complex solution behaviour, being in equilibrium with the homoleptic species ZnH2·IPr, Zn(HMDS)2 and IPr
Infrared Spectroscopy of Molecular Supernova Remnants
We present Infrared Space Observatory spectroscopy of sites in the supernova
remnants W28, W44, and 3C391, where blast waves are impacting molecular clouds.
Atomic fine-structure lines were detected from C, N, O, Si, P, and Fe. The S(3)
and S(9) lines of H2 were detected for all three remnants. The observations
require both shocks into gas with moderate (~ 100 /cm3) and high (~10,000 /cm3)
pre-shock densities, with the moderate density shocks producing the ionic lines
and the high density shock producing the molecular lines. No single shock model
can account for all of the observed lines, even at the order of magnitude
level. We find that the principal coolants of radiative supernova shocks in
moderate-density gas are the far-infrared continuum from dust grains surviving
the shock, followed by collisionally-excited [O I] 63.2 and [Si II] 34.8 micron
lines. The principal coolant of the high-density shocks is
collisionally-excited H2 rotational and ro-vibrational line emission. We
systematically examine the ground-state fine structure of all cosmically
abundant elements, to explain the presence or lack of all atomic fine lines in
our spectra in terms of the atomic structure, interstellar abundances, and a
moderate-density, partially-ionized plasma. The [P II] line at 60.6 microns is
the first known astronomical detection. There is one bright unidentified line
in our spectra, at 74.26 microns. The presence of bright [Si II] and [Fe II]
lines requires partial destruction of the dust. The required gas-phase
abundance of Fe suggests 15-30% of the Fe-bearing grains were destroyed. The
infrared continuum brightness requires ~1 Msun of dust survives the shock,
suggesting about 1/3 of the dust mass was destroyed, in agreement with the
depletion estimate and with theoretical models for dust destruction.Comment: 40 pages; 10 figures; accepted by ApJ July 11, 200
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