Sergio Cuevas

Minimization of entropy generation by asymmetric convective cooling

The uniform internal heating of a solid slab and the viscous flow between two parallel walls, are used to illustrate the possibility of minimizing the global entropy generation rate by cooling the external surfaces convectively in an asymmetric way. The known analytic expressions for the temperature field, in the first case, and the velocity and temperature fields, in the second case, are used to calculate the global entropy generation rate explicitly. In dimensionless terms, this function depends on the dimensionless ambient temperature and convective heat transfer coefficients (Biot numbers) of each surface which, in general, are not assumed to be the same. When the Biot numbers for each surface are equal, the entropy generation rate shows a monotonic increase. However, when the Biot numbers are different this function displays a minimum for specific cooling conditions.

Entropy generation analysis of magnetohydrodynamic induction devices

Magnetohydrodynamic (MHD) induction devices such as electromagnetic pumps or electric generators are analysed within the approach of entropy generation. The flow of an electrically-conducting incompressible fluid in an MHD induction machine is described through the well known Hartmann model. Irreversibilities in the system due to ohmic dissipation, flow friction and heat flow are included in the entropy-generation rate. This quantity is used to define an overall efficiency for the induction machine that considers the total loss caused by process irreversibility. For an MHD generator working at maximum power output with walls at constant temperature, an optimum magnetic field strength (i.e. Hartmann number) is found based on the maximum overall efficiency.

Breast cancer proteomics reveals a positive correlation between glyoxalase 1 expression and high tumor grade

Breast cancer is the neoplasia with the highest incidence in women worldwide. Proteomics approaches have accelerated the discovery of diagnostic and prognostic biomarkers. Here, we compared the proteomic profiles of breast tumors versus non-tumoral tissues in order to identify modulated proteins, which could represent potential markers associated to clinical features. By two-dimensional electrophoresis, we detected 28 differentially expressed proteins. Among these, 21 proteins were up-regulated and 7 were down-regulated in tumors (p<0.05). Proteins were identified using LC/ESI-MS/MS tandem mass spectrometry. One protein was identified as glyoxalase 1 (GLO1), an enzyme involved in detoxification of methylglyoxal, a cytotoxic product of glycolysis. GLO1 overexpression was confirmed by western blot assays in paired normal and tumor breast tissues in clinical stages I-III, and by immunohistochemistry on tissue microarrays (TMA) comprising a cohort of 98 breast tumors and 20 healthy specimens. Results from TMA demonstrated that GLO1 is overexpressed in 79% of tumors. Interestingly, GLO1 up-regulation correlates with advanced tumor grade (p<0.05). These findings demonstrate the association of GLO1 overexpression with tumor grade and pointed out for additional studies to establish the importance of GLO1 in breast cancer.

Optimization analysis of an alternate magnetohydrodynamic generator

The production of electric power through the oscillatory motion of an electrically conducting fluid in a continuous electrode Faraday generator is considered. The performance of this alternate magnetohydrodynamic (MHD) generator is analyzed using the conventional isotropic electrical efficiency and an overall second law efficiency, based on the global entropy generation rate. The velocity, electric current density and temperature fields for the oscillatory Hartmann flow are calculated in order to assess, in terms of the entropy generation rate, the dissipative phenomena caused by fluid friction, Joule heating and heat transfer in the MHD generator. The overall second law efficiency is used to determine optimum operation conditions that minimize process irreversibilities.

Induced electric current-based formulation in computations of low magnetic Reynolds number magnetohydrodynamic flows

We use the induced electric current as the main electromagnetic variable to compute low magnetic Reynolds number magnetohydrodynamic (MHD) flows. The equation for the induced electric current is derived by taking the curl of the induction equation and using Amperes law. Boundary conditions on the induced electric current are derived at the interface between the liquid and the thin conducting wall by considering the current loop closing in the wall and the adjacent liquid. These boundary conditions at the liquid-solid interface include the Robin boundary condition for the wall-normal component of the current and an additional equation for the wall potential to compute the tangential current component. The suggested formulation (denominated j-formulation) is applied to three common types of MHD wall-bounded flows by implementing the finite-difference technique: (i) high Hartmann number fully developed flows in a rectangular duct with conducting walls; (ii) quasi-two-dimensional duct flow in the entry into a magnet; and (iii) flow past a magnetic obstacle. Comparisons have been performed against the traditional formulation based on the induced magnetic field (B-formulation), demonstrating very good agreement.

Electrically driven vortices in a weak dipolar magnetic field in a shallow electrolytic layer

Steady dipolar vortices continuously driven by electromagnetic forcing in a shallow layer of an electrolytic fluid are studied experimentally and theoretically. The driving Lorentz force is generated by the interaction of a dc uniform electric current injected in the thin layer and the non-uniform magnetic field produced by a small dipolar permanent magnet (0.33 T). Laminar velocity profiles in the neighbourhood of the zone affected by the magnetic field were obtained with particle image velocimetry in planes parallel and normal to the bottom wall. Flow planes at different depths of the layer were explored for injected currents ranging from 10 to 100 mA. Measurements of the boundary layer attached to the bottom wall reveal that owing to the variation of the field in the normal direction, a slightly flattened developing profile with no shear stresses at the free surface is formed. A quasi-two-dimensional magnetohydrodynamic numerical model that introduces the non-uniformity of the magnetic field, particularly its decay in the normal direction, was developed. Vertical diffusion produced by the bottom friction was modelled through a linear friction term. The model reproduces the main characteristic behaviour of the electromagnetically forced flow.

Methylation Landscape of Human Breast Cancer Cells in Response to Dietary Compound Resveratrol

Aberrant DNA methylation is a frequent epigenetic alteration in cancer cells that has emerged as a pivotal mechanism for tumorigenesis. Accordingly, novel therapies targeting the epigenome are being explored with the aim to restore normal DNA methylation patterns on oncogenes and tumor suppressor genes. A limited number of studies indicate that dietary compound resveratrol modulates DNA methylation of several cancer-related genes; however a complete view of changes in methylome by resveratrol has not been reported yet. In this study we performed a genome-wide survey of DNA methylation signatures in triple negative breast cancer cells exposed to resveratrol. Our data showed that resveratrol treatment for 24 h and 48 h decreased gene promoter hypermethylation and increased DNA hypomethylation. Of 2476 hypermethylated genes in control cells, 1,459 and 1,547 were differentially hypomethylated after 24 h and 48 h, respectively. Remarkably, resveratrol did not induce widespread non-specific DNA hyper- or hypomethylation as changes in methylation were found in only 12.5% of 27,728 CpG loci. Moreover, resveratrol restores the hypomethylated and hypermethylated status of key tumor suppressor genes and oncogenes, respectively. Importantly, the integrative analysis of methylome and transcriptome profiles in response to resveratrol showed that methylation alterations were concordant with changes in mRNA expression. Our findings reveal for the first time the impact of resveratrol on the methylome of breast cancer cells and identify novel potential targets for epigenetic therapy. We propose that resveratrol may be considered as a dietary epidrug as it may exert its anti-tumor activities by modifying the methylation status of cancer -related genes which deserves further in vivo characterization.

Viscoelastic Effects on the Entropy Production in Oscillatory Flow between Parallel Plates with Convective Cooling

The heat transfer problem of a zero-mean oscillatory flow of a Maxwell fluid between infinite parallel plates with boundary conditions of the third kind is considered. With these conditions, the amount of heat entering or leaving the system depends on the external temperature as well as on the convective heat transfer coefficient. The local and global time-averaged entropy production are computed, and the consequences of convective cooling of the plates are also assessed. It is found that the global entropy production is a minimum for certain suitable combination of the physical parameters. For a discrete set of values of the oscillatory Reynolds number, the extracted heat from one of the plates shows maxima.

Electromagnetically driven oscillatory shallow layer flow

We report experimental observations of the laminar flow in a thin horizontal layer of electrolyte, generated by a time-periodic Lorentz force produced by an alternate, unidirectional electric current and the field of a small permanent magnet. The force drives a periodically oscillating dipolar vortex which displays some spatial and temporal symmetries. The attention is focused on the motion of the oscillatory layer in vertical planes perpendicular to both the bottom wall and the injected current. For different frequencies of the injected current, velocity fields were obtained using particle image velocimetry in the zone of more intense magnetic field as well as close to the edges of the magnet where the inhomogeneity of the field is more pronounced. Velocity profiles as functions of the normal coordinate are determined in characteristic points at different phases and oscillation frequencies. Experimental results are compared with a simple analytical solution and a full three-dimensional numerical simulati...

Chaotic advection at large Péclet number: Electromagnetically driven experiments, numerical simulations, and theoretical predictions

We present a combination of experiment, theory, and modelling on laminar mixing at large Peclet number. The flow is produced by oscillating electromagnetic forces in a thin electrolytic fluid layer, leading to oscillating dipoles, quadrupoles, octopoles, and disordered flows. The numerical simulations are based on the Diffusive Strip Method (DSM) which was recently introduced (P. Meunier and E. Villermaux, “The diffusive strip method for scalar mixing in two-dimensions,” J. Fluid Mech. 662, 134–172 (2010)) to solve the advection-diffusion problem by combining Lagrangian techniques and theoretical modelling of the diffusion. Numerical simulations obtained with the DSM are in reasonable agreement with quantitative dye visualization experiments of the scalar fields. A theoretical model based on log-normal Probability Density Functions (PDFs) of stretching factors, characteristic of homogeneous turbulence in the Batchelor regime, allows to predict the PDFs of scalar in agreement with numerical and experimenta...