40 research outputs found
Fresh concrete pumping arrest investigation for thixotropy by a CFD modelling apporach
Concrete pumping operations determine construction speed, finishing
quality, durability and even structural integrity. When pumping operations
cannot be continued, most problems occur due to complex time-dependent
transformations. This causes significant industrial costs (e.g. material and delay).
Since time-dependent aspects are currently not fully understood and cannot be
predicted, a way to quantify time-dependent aspects is needed. Therefore, we
make an attempt by numerical simulation by comparing thixotropic cases with
different pumping arresting times. After an introduction to fresh concrete rheology
and numerical modelling, ten representative thixotropy cases are analysed.
Despite some unresolved numerical instabilities, the numerical framework
allows to estimate pumping pressure peaks after resting time. The results
evaluate a thixotropy model, which is generally applicable for less thixotropic
SCC’s. It is clear that flow re-initiation after rest in concrete pumping is poorly
understood. Numerical simulation could be one approach for further analysis
and is potentially important for practice. Future work such as simulation of
concrete mixers, pressure increase after pumping arrest, formwork pressure
decay and leakage are therefore recommended
Phenomenology and physical origin of shear-localization and shear-banding in complex fluids
We review and compare the phenomenological aspects and physical origin of
shear-localization and shear-banding in various material types, namely
emulsions, suspensions, colloids, granular materials and micellar systems. It
appears that shear-banding, which must be distinguished from the simple effect
of coexisting static-flowing regions in yield stress fluids, occurs in the form
of a progressive evolution of the local viscosity towards two significantly
different values in two adjoining regions of the fluids in which the stress
takes slightly different values. This suggests that from a global point of view
shear-banding in these systems has a common physical origin: two physical
phenomena (for example, in colloids, destructuration due to flow and
restructuration due to aging) are in competition and, depending on the flow
conditions, one of them becomes dominant and makes the system evolve in a
specific direction.Comment: The original publication is available at http://www.springerlink.co
HBO1 is required for the maintenance of leukaemia stem cells.
Acute myeloid leukaemia (AML) is a heterogeneous disease characterized by transcriptional dysregulation that results in a block in differentiation and increased malignant self-renewal. Various epigenetic therapies aimed at reversing these hallmarks of AML have progressed into clinical trials, but most show only modest efficacy owing to an inability to effectively eradicate leukaemia stem cells (LSCs)1. Here, to specifically identify novel dependencies in LSCs, we screened a bespoke library of small hairpin RNAs that target chromatin regulators in a unique ex vivo mouse model of LSCs. We identify the MYST acetyltransferase HBO1 (also known as KAT7 or MYST2) and several known members of the HBO1 protein complex as critical regulators of LSC maintenance. Using CRISPR domain screening and quantitative mass spectrometry, we identified the histone acetyltransferase domain of HBO1 as being essential in the acetylation of histone H3 at K14. H3 acetylated at K14 (H3K14ac) facilitates the processivity of RNA polymerase II to maintain the high expression of key genes (including Hoxa9 and Hoxa10) that help to sustain the functional properties of LSCs. To leverage this dependency therapeutically, we developed a highly potent small-molecule inhibitor of HBO1 and demonstrate its mode of activity as a competitive analogue of acetyl-CoA. Inhibition of HBO1 phenocopied our genetic data and showed efficacy in a broad range of human cell lines and primary AML cells from patients. These biological, structural and chemical insights into a therapeutic target in AML will enable the clinical translation of these findings
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
Viscoplastic properties of laponite-CMC mixes
In this dataset, 15 samples of laponite-CMC mixes were realized and their viscoplastic properties are determined. Rheological parameters are then expressed as a function of age and components concentrations
Effect of Coarse Particle Volume Fraction on the Yield Stress of Muddy Sediments from Marennes Oléron Bay
Coastal erosion results from a combination of various factors, both natural and humaninduced, which have different time and space patterns. In addition, uncertainties still remain about the interactions of the forcing agents, as well as on the significance of non-local causes of erosion. We focused about the surface sediments in the Marennes Oléron bay, after a general description of the site that has many various activities. The superficial sediments show a mechanical behavior, mainly depends on the fine fraction for a composition that contains up to 60% of sandy material. Fine sediments fraction has a typical yield stress depending naturally of concentration or water content. This yield could be modified slightly or significantly by adding silt or sand. As a result, the rheological measurement sensitivity allows us to characterize five typical sediments that correlate with solid fraction and fine fraction
Stereoscopic measurement of free surface flows
The present paper adresses the problem of combined three-dimensionnal
measurements of shape and velocity of moving free surfaces. A measurement method
based on the cross-correlation of image pairs obtained from a calibrated
stereoscopic vision system is presented. The underlying concept of the method
consists in the generation of parametric shape and displacement forms which are
directly projected on the camera models. This procedure is then integrated in an
iterative optimization process so that elevation, orientation, curvature and
displacement of each surface subset are accurately estimated. Application is
made on inclined plane flows of complex non-Newtonian fluids as an alternative to
conventionnal rheometric devices
Stereoscopic measurement of free surface flows
The present paper adresses the problem of combined three-dimensionnal measurements of shape and velocity of moving free surfaces. A measurement method based on the cross-correlation of image pairs obtained from a calibrated stereoscopic vision system is presented. The underlying concept of the method consists in the generation of parametric shape and displacement forms which are directly projected on the camera models. This procedure is then integrated in an iterative optimization process so that elevation, orientation, curvature and displacement of each surface subset are accurately estimated. Application is made on inclined plane flows of complex non-Newtonian fluids as an alternative to conventionnal rheometric devices
Modelling thixotropic behavior of fresh cement pastes from MRI measurements
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