1,721,458 research outputs found
Drop shape under slow steady shear flow and during relaxation. Experimental results and comparison with theory
No full textThe three-dimensional small deformation of a single Newtonian drop immersed in an immiscible Newtonian liquid was investigated, both in slow steady shear and during retraction after cessation of shear. The experiments were performed in a parallel plate apparatus equipped with video-enhanced microscopy. The drop was observed from two perpendicular directions, and accurate measurements were obtained in each view by image analysis. The results were compared to existing theoretical predictions from the exact fluidodynamic problem, obtained perturbatively for the case of small deformations of the drop. Excellent agreement between data and theory was found, thus providing the first assessment of drop shape predictions in steady flow and relaxation for Newtonian fluids
Drop shape under slow steady shear flow and during relaxation. Experimental results and comparison with theory
No full textThe three-dimensional small deformation of a single Newtonian drop immersed in an immiscible Newtonian liquid was investigated, both in slow steady shear and during retraction after cessation of shear. The experiments were performed in a parallel plate apparatus equipped with video-enhanced microscopy. The drop was observed from two perpendicular directions, and accurate measurements were obtained in each view by image analysis. The results were compared to existing theoretical predictions from the exact fluidodynamic problem, obtained perturbatively for the case of small deformations of the drop. Excellent agreement between data and theory was found, thus providing the first assessment of drop shape predictions in steady flow and relaxation for Newtonian fluids
Drop shape under slow steady shear flow and during relaxation. Experimental results and comparison with theory
No full textThe three-dimensional small deformation of a single Newtonian drop immersed in an immiscible Newtonian liquid was investigated, both in slow steady shear and during retraction after cessation of shear. The experiments were performed in a parallel plate apparatus equipped with video-enhanced microscopy. The drop was observed from two perpendicular directions, and accurate measurements were obtained in each view by image analysis. The results were compared to existing theoretical predictions from the exact fluidodynamic problem, obtained perturbatively for the case of small deformations of the drop. Excellent agreement between data and theory was found, thus providing the first assessment of drop shape predictions in steady flow and relaxation for Newtonian fluids
Ellipsoidal drop model for single drop dynamics with non-Newtonian fluids
No full textA phenomenol. model for the dynamics of a single drop immersed in an immiscible matrix is proposed with the two incompressible component liqs. being in general viscoelastic. The model is formulated by assuming that the drop is always ellipsoidal, and the model parameters are detd. once and for all in the small deformation limit. The model is thereafter applicable to whatever flow condition is imposed at infinity, and for whatever intensity of flow field. Predictions of steady state deformation, drop breakup, and drop relaxation display the effects of constitutive elasticity on the drop dynamics
DYNAMICS OF A LIQUID DROP IN A FLOWING IMMISCIBLE LIQUID
No full textIn this article we discuss the dynamics of a single drop immersed in an immiscible fluid with a given velocity field at infinity. Drop relaxation is also discussed. Newtonian and non-Newtonian fluid components are considered, to examine the effects of constitutive elasticity on drop deformation modes. Both experimental and theoretical results are reviewed. We illustrate in some detail three main issues of research of the last decade, namely, the exploitation of rheo-optical techniques, the study of large deformations and break-up, through numerical simulations, and the advancements in single drop theory for the case of non- Newtonian fluid components
Rheology of Multiphase Systems: Emulsions, Suspensions and Foams
No full textThis chapter gives a survey on the rheology of multiphase systems. The topic is of the utmost practical relevance, as flows of multiphase systems, e.g., solids in liquid, liquid-liquid or gas-liquid systems are encountered in a very wide range of applications. It is then evident the difficult task of gathering together sparse results while also unifying concepts and interpretations. We were thus forced to make a severe selection of main topics, and to leave out many arguments which, though interesting, appear to be of less general relevance. We are fully aware that such a selection is certainly biased from our own interests and fields of expertise; although we apologize for this anisotropic point of view, we believe this is unavoidable in any review chapter.
The chapter opens with a section devoted to suspensions of solids in liquids. In order to maintain the discussion as simple as possible, we consider the case of identical solid spheres as inclusions, by neglecting inertia and buoyancy. The section progresses from dilute to “dense” suspensions. The second section reports on the rheology of liquid-liquid suspensions, i.e., emulsions. The relevance of the dynamic nature of the interface is stressed throughout, from the disperse to the co-continuous morphology. Deformability of the interface, together with breakup and coalescence phenomena play the central role under flow. The chapter then closes with a rather brief introduction to foams, i.e., the case of gas-liquid systems at very high gas fraction.
Whenever theoretical analysis can be profitably used to describe experimental evidences, it has been included in some detail. The reader will notice how theoretical understanding progressively fade out while reaching the end of the chapter, somehow reflecting both the age of the subjects here addressed, and their intrinsic difficulties. Although the topics covered in this chapter are widespread, a unifying tool is often used (if not explicitly reported) for the rheological description, namely, the celebrated stress averaging procedure formalized by Batchelor (1970). Useful limiting behaviors and scaling arguments are presented as well. In the cases where no clear cut understanding can be found, phenomenological arguments and practical rules of thumb are reported to guide the reader
ARID1A supports the expression of YAP target genes by facilitating the binding of TEAD on enhancers in epithelial breast cells
Full text linkYAP plays a significant role as an oncogenic driver in a multitude of tumour types. In the majority of cases, its hyperactivity is not associated with any genomic abnormalities. Consequently, it can be reasonably suggested that the aberrant activity of YAP in cancer should be sought in epigenetic dysregulation. Although YAP lacks a DNA binding domain, it acts as a positive regulator of the transcription of a large set of target genes in conjunction with the DNA binding proteins of the TEAD family. Conversely, ARID1A, which is a key component of the SWI/SNF chromatin remodelling complex, is primarily regarded as a tumour suppressor gene, whose activity is inactivated by recurrent mutations in numerous cancer types. ARID1A is in fact necessary to support expression of genes involved in DNA damage response, cell growth control and several other processes. To date, numerous studies have demonstrated a functional interplay between these two factors in both physiological processes and oncogenesis. Nevertheless, no unified mechanistic model has been established, and instead, a context-dependent interplay has been observed. The present PhD project offers a novel account of the complex interplay between ARID1A and YAP activity in breast epithelial cells under high mechanical cues. The analysis of available ATAC-seq data from cancer cell lines revealed that the loss of ARID1A resulted in a slight global reduction in chromatin accessibility, which was predominantly observed at enhancer regions. An analysis of transcription factor motifs in the less accessible enhancers revealed that TEAD was among the top most enriched. Finally, cross-referencing ATAC-seq data with ChIP-seq for TEAD revealed that the loss of ARID1A in these TEAD-bound enhancers resulted in a pronounced reduction in accessibility. Our data on gene expression and GO term analysis direct us on a model in which ARID1A loss is detrimental for YAP-dependent biological processes like proliferation and migration in cells immortalised but non tumorigenic. Finally, we took advantage of ARID1A Knock Out clone to gain insights into the mechanism through which it regulates YAP dependent gene expression. Our data show that ARID1A enables TEAD-4 binding to the promoters of its main target gene CTGF. Taken together all this evidence supports a model in which ARID1A supports TEAD binding and therefore represents a prerequisite to support YAP transcriptional programme in cells experiencing high mechanical stress. This model is in agreement with previous observations suggesting that ARID1A is required in the early phases of tumorigenesis, while its loss confers a competitive advantage to cells in later stages of tumour progression. Further experimentation will be necessary to validate this model and to elucidate the effects of concomitant hyperactivation of YAP and loss of ARID1A in in vitro and in vivo models of cancer progression
Rheology of a dilute suspension of rigid spheres in a second order fluid
No full textThe stress tensor for a dil. suspension of buoyancy free, inertialess, nonBrownian, rigid spheres immersed in a viscoelastic liq. is detd. via a perturbative expansion. The perturbation parameter is the Deborah no. De, giving the ratio between the characteristic time of the liq. and the characteristic time of the imposed flow. The theor. predictions upto order De are validated through numerical simulations of continuity and momentum equations for the single sphere problem. The analytic expressions for the local fields of velocity, pressure, and stresses are successfully compared with the results obtained with finite element calcns. Bulk rheol. quantities from theory and simulations also show an excellent agreement with each other. Good agreement is found with respect to exptl. data from the literature, e.g., on bulk normal stresses for dil. suspensions in shear flow
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