1,959 research outputs found
A transient network of telechelic polymers and microspheres : structure and rheology
We study the structure and dynamics of a transient network composed of
droplets of microemulsion connected by telechelic polymers. The polymer induces
a bridging attraction between droplets without changing their shape. A
viscoelastic behaviour is induced in the initially liquid solution,
characterised in the linear regime by a stretched exponential stress
relaxation. We analyse this relaxation in the light of classical theories of
transient networks. The role of the elastic reorganisations in the deformed
network is emphasized. In the non linear regime, a fast relaxation dynamics is
followed by a second one having the same rate as in the linear regime. This
behaviour, under step strain experiments, should induce a non monotonic
behaviour in the elastic component of the stress under constant shear rate.
However, we obtain in this case a singularity in the flow curve very different
from the one observed in other systems, that we interpret in terms of fracture
behaviour.Comment: 9 pages, 4 figure
Time scales in shear banding of wormlike micelles
Transient stress and birefringence measurements are performed on wormlike micellar solutions that "shear band", i.e. undergo flow-induced coexistence of states of different viscosities along a constant stress "plateau". Three well-defined relaxation times are found after a strain rate step between two banded flow states on the stress plateau. Using the Johnson-Segalman model, we relate these time scales to three qualitatively different stages in the evolution of the bands and the interface between them: band destabilization, reconstruction of the interface, and travel of the fully formed interface. The longest timescale is then used to estimate the magnitude of the (unknown) "gradient" terms that must be added to constitutive relations to explain the history independence of the steady flow and the plateau stress selection
Entropic phase separation of linked beads
We study theoretically a model system of a transient network of microemulsion
droplets connected by telechelic polymers and explain recent experimental
findings. Despite the absence of any specific interactions between either the
droplets or polymer chains, we predict that as the number of polymers per drop
is increased, the system undergoes a first order phase separation into a dense,
highly connected phase, in equilibrium with dilute droplets, decorated by
polymer loops. The phase transition is purely entropic and is driven by the
interplay between the translational entropy of the drops and the
configurational entropy of the polymer connections between them. Because it is
dominated by entropic effects, the phase separation mechanism of the system is
extremely robust and does not depend on the particlular physical realization of
the network. The discussed model applies as well to other polymer linked
particle aggregates, such as nano-particles connected with short DNA linkers
The Authors' Reply to Letter to the Editor, Re:Biliary Bicarbonate, pH, and Glucose Are Suitable Biomarkers of Biliary Viability During Ex Situ Normothermic Machine Perfusion of Human Donor Livers
Obtenção de luteĂna, violaxantina e B-caroteno a partir de espinafre (Spinacea oleracea LINNEU).
The Emerging Role of Viability Testing During Liver Machine Perfusion
The transplant community continues to be challenged by the disparity between the need for liver transplantation and the shortage of suitable donor organs. At the same time, the number of unused donor livers continues to increase, most likely attributed to the worsening quality of these organs. To date, there is no reliable marker of liver graft viability that can predict good posttransplant outcomes. Ex situ machine perfusion offers additional data to assess the viability of donor livers before transplantation. Hence, livers initially considered unsuitable for transplantation can be assessed during machine perfusion in terms of appearance and consistency, hemodynamics, and metabolic and excretory function. In addition, postoperative complications such as primary nonfunction or posttransplant cholangiopathy may be predicted and avoided. A variety of viability criteria have been used in machine perfusion, and to date there is no widely accepted composition of criteria for clinical use. This review discusses potential viability markers for hepatobiliary function during machine perfusion, describes current limitations, and provides future recommendations for the use of viability criteria in clinical liver transplantation
Donor Diabetes and Prolonged Cold Ischemia Time Synergistically Increase the Risk of Graft Failure After Liver Transplantation
BACKGROUND: Both prolonged cold ischemia time (CIT) and donor history of diabetes mellitus (DM) are associated with reduced graft survival after liver transplantation. However, it is unknown whether the adverse effect of prolonged CIT on posttransplant graft survival is more pronounced after transplant with DM versus non-DM donor grafts.
METHODS: The study sample included 58 226 liver transplant recipients (2002-2015) from the Scientific Registry of Transplant Recipients. Multivariable Cox survival regression with interaction analysis was used to quantify the extent to which history of donor DM (n = 6478) potentiates the adverse effect of prolonged ( \u3e /=8 hours) CIT (n = 18 287) on graft survival.
RESULTS: Donor DM and CIT 8 hours or longer were each associated with increased risk of graft failure (GF) (adjusted hazard ratio [aHR], 1.19; 95% confidence interval [CI], 1.06-1.35 and aHR, 1.42; 95% CI, 1.32-1.53, respectively) compared with transplanted grafts without either risk factor. However, the combination of DM and CIT 8 hours or longer was associated with a higher risk of GF than either factor alone (aHR, 1.79; 95% CI, 1.55-2.06) and had a synergy index of 1.30. The interaction was significant on a multiplicative scale in the later postoperative period, days 31 to 365 (P = 0.047).
CONCLUSIONS: These results suggest that liver grafts from DM donors are more susceptible to the adverse effects of prolonged CIT than livers from non-DM donors. We need to be cognizant that they are more susceptible to ischemic injury, and this may be considered during the allocation process
Obtaining zeaxanthin and violaxanthin standards for high performance liquid chromatography from solanum pseudocapsicum and capsicum annuum.
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