100 research outputs found
Wall slip, shear banding, and instability in the flow of a triblock copolymer micellar solution
The shear flow of a triblock copolymer micellar solution (PEO--PPO--PEO
Pluronic P84 in brine) is investigated using simultaneous rheological and
velocity profile measurements in the concentric cylinder geometry. We focus on
two different temperatures below and above the transition temperature
which was previously associated with the apparition of a stress plateau in the
flow curve. (i) At C , the bulk flow remains homogeneous
and Newtonian-like, although significant wall slip is measured at the rotor
that can be linked to an inflexion point in the flow curve. (ii) At
C , the stress plateau is shown to correspond to stationary
shear-banded states characterized by two high shear rate bands close to the
walls and a very weakly sheared central band, together with large slip
velocities at the rotor. In both cases, the high shear branch of the flow curve
is characterized by flow instability. Interpretations of wall slip, three-band
structure, and instability are proposed in light of recent theoretical models
and experiments.Comment: 13 pages, 13 figure
Acute lyme infection presenting with amyopathic dermatomyositis and rapidly fatal interstitial pulmonary fibrosis: a case report
<p>Abstract</p> <p>Introduction</p> <p>Dermatomyositis has been described in the setting of lyme infection in only nine previous case reports. Although lyme disease is known to induce typical clinical findings that are observed in various collagen vascular diseases, to our knowledge, we believe that our case is the first presentation of acute lyme disease associated with amyopathic dermatomyositis, which was then followed by severe and fatal interstitial pulmonary fibrosis only two months later.</p> <p>Case presentation</p> <p>We present a case of a 64-year-old African-American man with multiple medical problems who was diagnosed with acute lyme infection after presenting with the pathognomonic rash and confirmatory serology. In spite of appropriate antimicrobial therapy for lyme infection, he developed unexpected amyopathic dermatomyositis and then interstitial lung disease.</p> <p>Conclusions</p> <p>This case illustrates a potential for lyme disease to produce clinical syndromes that may be indistinguishable from primary connective tissue diseases. An atypical and sequential presentation (dermatomyositis and interstitial lung disease) of a common disease (lyme infection) is discussed. This case illustrates that in patients who are diagnosed with lyme infection who subsequently develop atypical muscular, respiratory or other systemic complaints, the possibility of severe rheumatological and pulmonary complications should be considered.</p
RAFT aqueous dispersion polymerization yields poly(ethylene glycol)-based diblock copolymer nano-objects with predictable single phase morphologies
A poly(ethylene glycol) (PEG) macromolecular chain transfer agent (macro-CTA) is prepared in high yield (>95%) with 97% dithiobenzoate chain-end functionality in a three-step synthesis starting from a monohydroxy PEG113 precursor. This PEG113-dithiobenzoate is then used for the reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA). Polymerizations conducted under optimized conditions at 50 °C led to high conversions as judged by 1H NMR spectroscopy and relatively low diblock copolymer polydispersities (Mw/Mn < 1.25) as judged by GPC. The latter technique also indicated good blocking efficiencies, since there was minimal PEG113 macro-CTA contamination. Systematic variation of the mean degree of polymerization of the core-forming PHPMA block allowed PEG113-PHPMAx diblock copolymer spheres, worms, or vesicles to be prepared at up to 17.5% w/w solids, as judged by dynamic light scattering and transmission electron microscopy studies. Small-angle X-ray scattering (SAXS) analysis revealed that more exotic oligolamellar vesicles were observed at 20% w/w solids when targeting highly asymmetric diblock compositions. Detailed analysis of SAXS curves indicated that the mean number of membranes per oligolamellar vesicle is approximately three. A PEG 113-PHPMAx phase diagram was constructed to enable the reproducible targeting of pure phases, as opposed to mixed morphologies (e.g., spheres plus worms or worms plus vesicles). This new RAFT PISA formulation is expected to be important for the rational and efficient synthesis of a wide range of biocompatible, thermo-responsive PEGylated diblock copolymer nano-objects for various biomedical applications
The effect of the geomagnetic field on cosmic ray energy estimates and large scale anisotropy searches on data from the Pierre Auger Observatory
We present a comprehensive study of the influence of the geomagnetic field on
the energy estimation of extensive air showers with a zenith angle smaller than
, detected at the Pierre Auger Observatory. The geomagnetic field
induces an azimuthal modulation of the estimated energy of cosmic rays up to
the ~2% level at large zenith angles. We present a method to account for this
modulation of the reconstructed energy. We analyse the effect of the modulation
on large scale anisotropy searches in the arrival direction distributions of
cosmic rays. At a given energy, the geomagnetic effect is shown to induce a
pseudo-dipolar pattern at the percent level in the declination distribution
that needs to be accounted for.Comment: 20 pages, 14 figure
Histamine and histamine methyltransferase in the gastric mucosa of man, pig, dog and cow
Recent experimental probes of shear banding
Recent experimental techniques used to investigate shear banding are
reviewed. After recalling the rheological signature of shear-banded flows, we
summarize the various tools for measuring locally the microstructure and the
velocity field under shear. Local velocity measurements using dynamic light
scattering and ultrasound are emphasized. A few results are extracted from
current works to illustrate open questions and directions for future research.Comment: Review paper, 23 pages, 11 figures, 204 reference
A phylogenetic study on the occurrence and distribution of histamine in the gastro-intestinal tract and other tissues of man and various animals
Transient behavior and relaxations of the L (sponge) phase : T-jumb experiments
We report here on a systematic time resolved investigation of the transient behavior of the sponge phase after an abrupt temperature jump. We obtain evidence for three distinct relaxation times and having very different magnitudes. We show that is related to a conserved internal variable while and both correspond to the relaxations of unconserved thermodynamic variables. We propose an interpretation of the transient behavior based on the idea that the temperature jump essentially puts the membrane in L under transient tension. According to this interpretation, corresponds to the relaxation of concentration fluctuations, to that of the degree of symmetry of the structure and to that of its density of connectivity. This picture actually accounts at least qualitatively for the experimental observation. Moreover, the temperature dependences of and close to the sponge-to-lamellar transition temperature indicate that this transition is quite weakly first order
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