Shell Model for Drag Reduction with Polymer Additive in Homogeneous Turbulence

Recent direct numerical simulations of the FENE-P model of non-Newtonian hydrodynamics revealed that the phenomenon of drag reduction by polymer additives exists (albeit in reduced form) also in homogeneous turbulence. We introduce here a simple shell model for homogeneous viscoelastic flows that recaptures the essential observations of the full simulations. The simplicity of the shell model allows us to offer a transparent explanation of the main observations. It is shown that the mechanism for drag reduction operates mainly on the large scales. Understanding the mechanism allows us to predict how the amount of drag reduction depends of the various parameters in the model. The main conclusion is that drag reduction is not a universal phenomenon, it peaks in a window of parameters like Reynolds number and the relaxation rate of the polymer

A simple model for drag reduction

Direct Numerical Simulations established that the FENE-P model of viscoelastic flows exhibits the phenomenon of turbulent drag reduction which is caused in experiments by dilute polymeric additives. To gain analytic understanding of the phenomenon we introduce in this Letter a simple 1-dimensional model of the FENE-P equations. We demonstrate drag reduction in the simple model, and explain analytically the main observations which include (i) reduction of velocity gradients for fixed throughput and (ii) increase of throughput for fixed dissipation.Comment: submitted to PR

Circulating tumor cells : what is in It for the patient? : a vision towards the future

Knowledge on cellular signal transduction pathways as drivers of cancer growth and metastasis has fuelled development of "targeted therapy" which "targets" aberrant oncogenic signal transduction pathways. These drugs require nearly invariably companion diagnostic tests to identify the tumor-driving pathway and the cause of the abnormal pathway activity in a tumor sample, both for therapy response prediction as well as for monitoring of therapy response and emerging secondary drug resistance. Obtaining sufficient tumor material for this analysis in the metastatic setting is a challenge, and circulating tumor cells (CTCs) may provide an attractive alternative to biopsy on the premise that they can be captured from blood and the companion diagnostic test results are correctly interpreted. We discuss novel companion diagnostic directions, including the challenges, to identify the tumor driving pathway in CTCs, which in combination with a digital pathology platform and algorithms to quantitatively interpret complex CTC diagnostic results may enable optimized therapy response prediction and monitoring. In contrast to CTC-based companion diagnostics, CTC enumeration is envisioned to be largely replaced by cell free tumor DNA measurements in blood for therapy response and recurrence monitoring. The recent emergence of novel in vitro human model systems in the form of cancer-on-a-chip may enable elucidation of some of the so far elusive characteristics of CTCs, and is expected to contribute to more efficient CTC capture and CTC-based diagnostics. Keywords: cancer; metastasis; circulating tumor cell; CTC; digital pathology; companion diagnostics; cell-free DNA; organ-on-chip; computational pathway mode

The P-h2 relationship in indentation

In this paper we derive an anal. expression for the indentation load-depth relation during loading in an indentation expt., namely P = Er (1/C Er/H + e p/4 H/Er)-2 (h + x)2. The advantage over previously used expressions is that no addnl. empirical consts. are necessary. A comparison between the new expression and results from finite element calcns. shows excellent agreement

Determination of the elastic modulus and hardness of sol-gel coatings on glass: influence of indenter geometry

Indentations have been carried out on methyltrimethoxysilane coated float glass by using a spherical and a Berkovich indenter. The composite hardness as well as the effective elastic modulus were determined as a function of indentation depth for coatings of a thickness 0.5, 2 and 4 µm. Using the Berkovich indenter, the coating exhibited radial cracking (only for the two thicker coatings), delamination and chipping, whereas no cracking occurred during indentations using a spherical indenter. For the experiments in which the coatings exhibited radial cracking, we measured a constant composite hardness over the whole depth range instead of the expected increase. The elastic modulus, on the other hand, turned out to be insensitive to the radial cracking. All results show the expected increase of the modulus with indentation depth. The spherical indenter showed a much steeper rise of the effective elastic modulus with indentation depth than the (sharp) Berkovich indenter. By re-scaling the results with respect to contact area instead of indentation depth, the Berkovich and the sphere elastic moduli are comparable. Only at the point where delamination occurred in the Berkovich indentations, the re-scaled results of the two indenter geometries start to deviate

Determination of the elastic modulus and hardness of sol-gel coatings on glass: influence of indenter geometry

Indentations have been carried out on methyltrimethoxysilane coated float glass by using a spherical and a Berkovich indenter. The composite hardness as well as the effective elastic modulus were determined as a function of indentation depth for coatings of a thickness 0.5, 2 and 4 µm. Using the Berkovich indenter, the coating exhibited radial cracking (only for the two thicker coatings), delamination and chipping, whereas no cracking occurred during indentations using a spherical indenter. For the experiments in which the coatings exhibited radial cracking, we measured a constant composite hardness over the whole depth range instead of the expected increase. The elastic modulus, on the other hand, turned out to be insensitive to the radial cracking. All results show the expected increase of the modulus with indentation depth. The spherical indenter showed a much steeper rise of the effective elastic modulus with indentation depth than the (sharp) Berkovich indenter. By re-scaling the results with respect to contact area instead of indentation depth, the Berkovich and the sphere elastic moduli are comparable. Only at the point where delamination occurred in the Berkovich indentations, the re-scaled results of the two indenter geometries start to deviate

Elastic modulus, indentation pressure and fracture toughness of hybrid coatings on glass

The indentation load-displacement behavior of an org.-inorg. hybrid coating was tested using a Berkovich indenter in an attempt to offer a simple and fast method to analyze the mech. properties of a coating. The coatings were deposited using a spin-coating technique. The elastic modulus and the indentation pressure as a measure of the hardness were detd. on the basis of the load-displacement curve. The effects of the coating thickness and the coating prepn. conditions were investigated. Cracks, delamination and chipping were obsd. and were used to assess the fracture toughness of the coating and the interface. Elastic modulus, indentation pressure and the fracture toughness were dependent on the time elapsed before application of the coating fluid and on the curing temp

The effect of microchamber geometry on the efficiency of magnetic microbead mixing

The necessity for low-cost and user-friendly medical diagnostics has an impact on the development of innovative Lab-On-Chip technologies for in-vitro point-of-care diagnostic testing. The Philips Minicare I-20 platform for the diagnosis of myocardial infarction is such a system that provides precise, quantitative and fast results. The system is based on controlled movement of magnetic nanoparticles where the Troponin analyte is captured on the antibody coated particle and the detection is optical. In this way, the scheme supports quantitative results of Troponin in the patient’s drop of blood. Nevertheless, the efficiency of analyte biochemical binding is strongly dependent on the homogeneity of the reagents within the matrix, which, due to the low Reynolds numbers inside the microfluidic chip, is inefficient. The aim of our research is to solve this mixing problem by developing novel approaches to reach homogeneity of reagents to achieve high precision handheld diagnostics, in which we make use of the “magnetic infrastructure” of the system. In this report, we focus on the effect of the chip geometry of the microfluidic processing and detection chamber, in combination with optimized magnetic actuation protocols, on the overall mixing efficiency of the reagents. To investigate this, we carry our dedicated experiments with a unique magnetic actuation set-up, and we perform microscopic fluid flow characterization. It is expected that smart geometrical chip designs can positively affect active mixing and achieve homogeneity

Measuring mechanical properties of coatings : a methodology applied to nano-particle-filled sol-gel coatings on glass

The main aim of this paper is to demonstrate the practical use of nano-indentation and scratch testing in determining mechanical properties of thin coatings. We place our emphasis on how information obtained using both techniques can be combined to give a more complete representation of the properties of a coating–substrate system. Part I of the paper gives an overview of approaches to determine mechanical properties of thin coatings that have been proposed in the literature, and develops them further to be useful tools in the analysis of coatings. This results in methods for measuring the mechanical properties of thin coatings. We particularly emphasise the determination of the elastic modulus, hardness, coating and interfacial fracture toughness and residual stress using indentation and scratch testing. Part II of the paper illustrates the application of these methods to relatively soft coatings of methyltrimethoxysilane (MTMS) filled with colloidal silica or alumina particles on glass. The coatings were prepared using a sol–gel process. We report results of the dependence of the mechanical properties on the filler particle content, illustrating that microstructural changes can also be tracked using these techniques. The effects of the nature and volume fraction of the filler particles are discussed