Rhodotorula glutinis T13 as a potential source of microbial lipids for biodiesel generation.

Single cell oils (SCO) are a promising source of oils that could be exploited in different industrial areas. SCO for biodiesel production circumvents the controversy food vs. fuel, does not require large land areas for culture, and is independent of climate and seasonal variations, among other advantages in comparison to vegetable oils. In this study, a red yeast isolated from a mountain water source, identified as Rhodotorula glutinis T13, showed high potential for lipid production (40% w/w) with suitable growth parameters, yields, and fatty acids profile. Yeast lipids showed a high content of unsaturated fatty acids (56.44%; C18:1, C18:2), and the fuel properties (cetane number, iodine value, density, kinematic viscosity, etc.) of yeast oil analysed were in good agreement with international biodiesel standards. The results show that R. glutinis T13 can be used in the future as a promising microorganism for the commercial production of biodiesel.

Growth and lipid production of Rhodotorula glutinis R4, in comparison to other oleaginous yeasts.

Some Rhodotorula spp. have been characterized as oleaginous yeasts. Under certain culture conditions they can accumulate neutral lipids, which are mainly triglycerides (TAG). Microbial TAG that can be used as raw material for biodiesel synthesis are attractive for the biofuel industry. In this study, the ability to synthesize lipids of Rhodotorula glutinis R4, isolated in Antarctica, was compared with eight strains belonging to the genera Rhodotorula and Yarrowia with the aim of proposing a novel source of oils for biodiesel synthesis. All strains were cultured under nitrogen (N) limiting conditions and an excess of carbon (C) in the culture medium. We found that yeasts accumulated between 9-48.9 % (w/w) of lipids. Among them, R. glutinis R4 showed the highest growth (14 g L-1, µmax 0,092 h-1) and lipid production (7 g L-1; 47 % w/w). Microbial oils produced by R. glutinis R4 are similar to vegetable oils, with 61 % of oleic acid, indicating that it is adequate for biodiesel synthesis. Our results demonstrate that biodiesel derived from R. glutinis R4 complies with international fuel standards ASTM D6751 and EN 14214. Therefore, this work demonstrates that Rhodotorula glutinis R4 is a novel and valuable source of microbial oils for biodiesel synthesis.

Efecto genotóxico del material particulado PM2.5 recolectado en la zona urbana de Cuenca - Ecuador sobre la línea celular de ovario de hámster chino CHO-K1 / Genotoxic effect of PM2.5 particulate material collected in the urban area of the city of Cuenca - Ecuador in the Chinese hamster ovary cells line CHO-K1

Estudios toxicológicos y epidemiológicos ponen de manifiesto que el material particulado (PM) específicamente el PM2.5 tiene efectos negativos significativos en la salud humana, asociado con mortalidad, insuficiencia cardíaca, trastornos respiratorios, enfermedades pulmonares y cáncer. La toxicidad y el efecto inflamatorio de estas partículas están relacionados con su tamaño y características químicas. En este estudio se determinaron las características químicas de las fracciones acuosas y orgánicas solubles del PM2.5 recolectado en tres sitios de monitoreo del área urbana de la ciudad de Cuenca-Ecuador y se evaluó su actividad genotóxica mediante el ensayo del cometa en la línea celular de ovario de hámster chino, CHO-K1. El análisis gravimétrico de las muestras reveló que dos de los sitios de estudio superaron el límite de 25 mig/m3 establecido por la Organización Mundial de la Salud. En la caracterización de las fracciones acuosas y orgánicas se determinó la presencia de metales como el hierro y zinc e hidrocarburos aromáticos tales como el benzo(a) antraceno respectivamente. Las células fueron expuestas a 3,26 m3 de aire /mL de los extractos acuosos y 1,63 m3 de aire/mL de los extractos orgánicos. Finalmente se observó que los extractos obtenidos de PM2.5 inducen daño genotóxico en la longitud del largo de cola medido mediante el ensayo del cometa; este tipo de daño pueden atribuirse a la combinación de las especies químicas detectadas

Toxicological and epidemiological studies have a manifesto that particulate matter (PM), specifically PM2.5 has negative effects on human health, associated with mortality, heart failure, respiratory disorders, lung diseases, and cancer. The toxicity and inflammatory effect of these particles are related to their size and chemical characteristics. The objective of this study was to determine the characteristics of the soluble aqueous and organic fractions of the particulate material PM 2.5 collected in the monitoring sites of the urban area of ​​the city of Cuenca-Ecuador and to evaluate its genotoxic activity by means of the test of the comet of in the Chinese hamster ovary cells line CHO-K1. The gravimetric analysis of the samples revealed that two of the study sites exceeded the limit of 25 ug / m3 established by the WHO. In the characterization of water and organic fractions, the presence of metals such as Fe and Zn and aromatic hydrocarbons such as benzo(a) anthracene determined, respectively. Cells were exposed to 3,26 m3 of air /mL of aqueous extracts and 1,63 m3 of air/ mL of organic extracts. Finally, it was observed that the extracts obtained from PM2.5 induce genotoxic in the length of tail length measured by the comet assay; this type of damage can be attributed to the combination of the detected chemical species

Decoupling Geometrical and Kinematic Contributions to the Silo Clogging Process.

Based on the implementation of a novel silo discharge procedure, we are able to control the grains velocities regardless of the outlet size. This allows isolating the geometrical and kinematic contributions to the clogging process. We find that, for a given outlet size, reducing the grains velocities to extremely low values leads to a clogging probability increment of almost two orders of magnitude, hence revealing the importance of particle kinematics in the silo clogging process. Then, we explore the contribution of both variables, outlet size and grains velocity, and we find that our results agree with an already known exponential expression that relates clogging probability with outlet size. We propose a modification of such expression revealing that only two parameters are necessary to fit all the data: one is related with the geometry of the problem, and the other with the grains kinematics.

An instrument for studying granular media in low-gravity environment.

A new experimental facility has been designed and constructed to study driven granular media in a low-gravity environment. This versatile instrument, fully automatized, with a modular design based on several interchangeable experimental cells, allows us to investigate research topics ranging from dilute to dense regimes of granular media such as granular gas, segregation, convection, sound propagation, jamming, and rheology-all without the disturbance by gravitational stresses active on Earth. Here, we present the main parameters, protocols, and performance characteristics of the instrument. The current scientific objectives are then briefly described and, as a proof of concept, some first selected results obtained in low gravity during parabolic flight campaigns are presented.

Experimental Study of Ordering of Hard Cubes by Shearing.

We experimentally analyze the compaction dynamics of an ensemble of cubic particles submitted to a novel type of excitation. Instead of the standard tapping procedure used in granular materials we apply alternative twists to the cylindrical container. Under this agitation, the development of shear forces among the different layers of cubes leads to particle alignment. As a result, the packing fraction grows monotonically with the number of twists. If the intensity of the excitations is sufficiently large, an ordered final state is reached where the volume fraction is the densest possible compatible with the boundary condition. This ordered final state resembles the tetratic or cubatic phases observed in colloids.

Silo discharge of binary granular mixtures.

We present numerical and experimental results on the mass flow rate during the discharge of three-dimensional silos filled with a bidisperse mixture of grains of different sizes. We analyzed the influence of the ratio between coarse and fine particles on the profile of volume fraction and velocity across the orifice. By using numerical simulations, we have shown that the velocity profile has the same shape as that in the monodisperse case and is insensitive to the composition of the mixture. On the contrary, the volume fraction profile is strongly affected by the composition of the mixture. Assuming that an effective particle size can be introduced to characterize the mixture, we have shown that previous expression for the mass flow rate of monodisperse particles can be used for binary mixtures. A comparison with Beverloo's correlation is also presented.

Metabolic Reprogramming, Autophagy, and Reactive Oxygen Species Are Necessary for Primordial Germ Cell Reprogramming into Pluripotency.

Cellular reprogramming is accompanied by a metabolic shift from oxidative phosphorylation (OXPHOS) toward glycolysis. Previous results from our laboratory showed that hypoxia alone is able to reprogram primordial germ cells (PGCs) into pluripotency and that this action is mediated by hypoxia-inducible factor 1 (HIF1). As HIF1 exerts a myriad of actions by upregulating several hundred genes, to ascertain whether the metabolic switch toward glycolysis is solely responsible for reprogramming, PGCs were cultured in the presence of a pyruvate kinase M2 isoform (PKM2) activator, or glycolysis was promoted by manipulating PPARγ. Conversely, OXPHOS was stimulated by inhibiting PDK1 activity in normoxic or in hypoxic conditions. Inhibition or promotion of autophagy and reactive oxygen species (ROS) production was performed to ascertain their role in cell reprogramming. Our results show that a metabolic shift toward glycolysis, autophagy, and mitochondrial inactivation and an early rise in ROS levels are necessary for PGC reprogramming. All of these processes are governed by HIF1/HIF2 balance and strict intermediate Oct4 levels. Histone acetylation plays a role in reprogramming and is observed under all reprogramming conditions. The pluripotent cells thus generated were unable to self-renew, probably due to insufficient Blimp1 downregulation and a lack of Klf4 and cMyc expression.

Disentangling the Free-Fall Arch Paradox in Silo Discharge.

Several theoretical predictions of the mass flow rate of granular media discharged from a silo are based on the spontaneous development of a free-fall arch region, the existence of which is still controversial. In this Letter, we study experimentally and numerically the particle flow through an orifice placed at the bottom of 2D and 3D silos. The implementation of a coarse-grained technique allows a thorough description of all the kinetic and micromechanical properties of the particle flow in the outlet proximities. Though the free-fall arch does not exist as traditionally understood--a region above which particles have negligible velocity and below which particles fall solely under gravity action--we discover that the kinetic pressure displays a well-defined transition in a position that scales with the outlet size. This universal scaling explains why the free-fall arch picture has served as an approximation to describe the flow rate in the discharge of silos.

Cell metabolism under microenvironmental low oxygen tension levels in stemness, proliferation and pluripotency.

Hypoxia is defined as a reduction in oxygen supply to a tissue below physiological levels. However, physiological hypoxic conditions occur during early embryonic development; and in adult organisms, many cells such as bone marrow stem cells are located within hypoxic niches. Thus, certain processes take place in hypoxia, and recent studies highlight the relevance of hypoxia in stem cell cancer physiology. Cellular response to hypoxia depends on hypoxia-inducible factors (HIFs), which are stabilized under low oxygen conditions. In a hypoxic context, various inducible HIF alpha subunits are able to form dimers with constant beta subunits and bind the hypoxia response elements (HRE) in the genome, acting as transcription factors, inducing a wide variety of gene expression. Typically, the HIF pathway has been shown to enhance vascular endothelial growth factor (VEGF) expression, which would be responsible for angiogenesis and, therefore, re-oxygenation of the hypoxic sites. Embryonic stem cells inhibit a severely hypoxic environment, which dictates their glycolytic metabolism, whereas differentiated cells shift toward the more efficient aerobic respiration for their metabolic demands. Accordingly, low oxygen tension levels have been reported to enhance induced pluripotent stem cell (iPS) generation. HIFs have also been shown to enhance pluripotency-related gene expression, including Oct4 (Octamer-binding transcription factor 4), Nanog and Wnt. Therefore, cell metabolism might play a role in stemness maintenance, proliferation and cell reprogramming. Moreover, in the hypoxic microenvironment of cancer cells, metabolism shifts from oxidative phosphorylation to anaerobic glycolysis, a process known as the Warburg effect, which is involved in cancer progression and malignancy.

Influence of the feeding mechanism on deposits of square particles.

In a previous paper [Hidalgo et al., Phys. Rev. Lett. 103, 118001 (2009)] it was shown that square particles deposited in a silo tend to align with a diagonal parallel to the gravity, giving rise to a deposit with very particular properties. Here we explore, both experimentally and numerically, the effect on these properties of the filling mechanism. In particular, we modify the volume fraction of the initial configuration from which the grains are deposited. Starting from a very dilute case, increasing the volume fraction results in an enhancement of the disorder in the final deposit characterized by a decrease of the final packing fraction and a reduction of the number of particles oriented with their diagonal in the direction of gravity. However, for very high initial volume fractions, the final packing fraction increases again. This result implies that two deposits with the same final packing fraction can be obtained from very different initial conditions. The structural properties of such deposits are analyzed, revealing that, although the final volume fraction is the same, their micromechanical properties notably differ.

Stress distribution of faceted particles in a silo after its partial discharge.

We present experimental and numerical results of the effect that a partial discharge has on the morphological and micro-mechanical properties of non-spherical, convex particles in a silo. The comparison of the particle orientation after filling the silo and its subsequent partial discharge reveals important shear-induced orientation, which affects stress propagation. For elongated particles, the flow induces an increase in the packing disorder which leads to a reduction of the vertical stress propagation developed during the deposit generated prior to the partial discharge. For square particles, the flow favors particle alignment with the lateral walls promoting a behavior opposite to the one of the elongated particles: vertical force transmission, parallel to gravity, is induced. Hence, for elongated particles the flow developed during the partial discharge of the silo leads to force saturation with depth whereas for squares the flow induces hindering of the force saturation observed during the silo filling.

Flow-rate fluctuations in the outpouring of grains from a two-dimensional silo.

We present experimental results obtained with a two-dimensional silo discharging under gravity through an orifice at the flat bottom. High-speed measurements provide enough time resolution to detect every single bead that goes out and this allows the measurement of the flow rate in short-time windows. Two different regimes are clearly distinguished: one for large orifices, which can be described by Gaussian fluctuations, and another for small orifices, in which extreme events appear. The frontier between those two regimes coincides with the outlet size below which jamming events are frequent. Moreover, it is shown that the power spectrum of the flow-rate oscillations is not dominated by any particular frequency.

Anomalous diffusion in silo drainage.

The silo discharge process is studied by molecular dynamics simulations. The development of the velocity profile and the probability density function for the displacements in the horizontal and vertical axis are obtained. The PDFs obtained at the beginning of the discharge reveal non-Gaussian statistics and superdiffusive behaviors. When the stationary flow is developed, the PDFs at shorter temporal scales are non-Gaussian too. For big orifices a well-defined transition between ballistic and diffusive regime is observed. In the case of a small outlet orifice, no well-defined transition is observed. We use a nonlinear diffusion equation introduced in the framework of non-extensive thermodynamics in order to describe the movements of the grains. The solution of this equation gives a well-defined relationship (gamma = 2/(3 - q)) between the anomalous diffusion exponent gamma and the entropic parameter q introduced by the non-extensive formalism to fit the PDF of the fluctuations.

Convective motion in a vibrated granular layer.

Velocity measurements are presented for a vertically shaken granular layer. For frequencies around 110 Hz and accelerations larger than gravity, the layer develops a convective motion in the form of one or more rolls. The velocity of the grains near the wall has been measured. It grows linearly with the acceleration, then the growth rate slows down. A rescaling with the amplitude of the wall velocity and the height of the granular layer makes all data collapse in a single curve.

Synchronization of chaotic structurally nonequivalent systems

Synchronization features are explored for a pair of chaotic high-dimensional bidirectionally coupled structurally nonequivalent systems. We find two regimes of synchronization in dependence on the coupling strength: creation of a lower dimensional chaotic state, and for larger coupling a transition toward a stable periodic motion. We characterize this new state, showing that it is associated with an abrupt transition in the Lyapunov spectrum. The robustness of this state against noise is discussed, and the use of this dynamical property as a possible approach for the control of chaos is outlined.

Experimental phase synchronization of a chaotic convective flow.

We report experimental evidence of phase synchronization of high dimensional chaotic oscillators in a laboratory experiment. The experiment consists of a thermocapillary driven convective cell in a time dependent chaotic regime. The synchronized states emerge as a consequence of a localized temperature perturbation to the heater. The transition to phase synchronization is studied as a function of the external perturbations. The existence and stability conditions for this phenomenon are discussed.

Patterns in small aspect ratio Bénard-Marangoni convection.

An experimental study of pattern formation in Bénard-Marangoni convection with small aspect ratio containers and high Prandtl number fluids is presented. The observed stationary patterns complete previous experimental works performed at different values of aspect ratio and supercriticality. Detailed experimental studies of the flow in some single structures are described, and spatial bifurcations between different stationary planforms for a fixed aspect ratio are shown. These experimental results agree qualitatively with linear theory analysis and with some previous numerical works about boundary conditions effects.