The Dynamics of Hybrid Metabolic-Genetic Oscillators

The synthetic construction of intracellular circuits is frequently hindered by a poor knowledge of appropriate kinetics and precise rate parameters. Here, we use generalized modeling (GM) to study the dynamical behavior of topological models of a family of hybrid metabolic-genetic circuits known as "metabolators." Under mild assumptions on the kinetics, we use GM to analytically prove that all explicit kinetic models which are topologically analogous to one such circuit, the "core metabolator," cannot undergo Hopf bifurcations. Then, we examine more detailed models of the metabolator. Inspired by the experimental observation of a Hopf bifurcation in a synthetically constructed circuit related to the core metabolator, we apply GM to identify the critical components of the synthetically constructed metabolator which must be reintroduced in order to recover the Hopf bifurcation. Next, we study the dynamics of a re-wired version of the core metabolator, dubbed the "reverse" metabolator, and show that it exhibits a substantially richer set of dynamical behaviors, including both local and global oscillations. Prompted by the observation of relaxation oscillations in the reverse metabolator, we study the role that a separation of genetic and metabolic time scales may play in its dynamics, and find that widely separated time scales promote stability in the circuit. Our results illustrate a generic pipeline for vetting the potential success of a potential circuit design, simply by studying the dynamics of the corresponding generalized model

A geometric construction of traveling waves in a bioremediation.

Bioremediation is a promising technique for cleaning contaminated soil. We study an idealized bioremediation model involving a substrate (contaminant to be removed), electron acceptor (added nutrient), and microorganisms in a one-dimensional soil column. Using geometric singular perturbation theory, we construct traveling waves (TW) corresponding to motion of a biologically active zone, in which the microorganisms consume both substrate and acceptor. For certain values of the parameters, the traveling waves exist on a three-dimensional slow manifold within the five-dimensional phase space. We prove persistence of the slow manifold under perturbation by controlling the nonlinearity via a change of coordinates, and we construct the wave in the transverse intersection of appropriate stable and unstable manifolds in this slow manifold. We study how the TW depends on the half saturation constants and other parameters and investigate numerically a bifurcation in which the TW loses stability to a periodic wav

Axisymmetric equilibria of a gravitating plasma with incompressible flows

It is found that the ideal magnetohydrodynamic equilibrium of an axisymmetric gravitating magnetically confined plasma with incompressible flows is governed by a second-order elliptic differential equation for the poloidal magnetic flux function containing five flux functions coupled with a Poisson equation for the gravitation potential, and an algebraic relation for the pressure. This set of equations is amenable to analytic solutions. As an application, the magnetic-dipole static axisymmetric equilibria with vanishing poloidal plasma currents derived recently by Krasheninnikov, Catto, and Hazeltine [Phys. Rev. Lett. {\bf 82}, 2689 (1999)] are extended to plasmas with finite poloidal currents, subject to gravitating forces from a massive body (a star or black hole) and inertial forces due to incompressible sheared flows. Explicit solutions are obtained in two regimes: (a) in the low-energy regime $\beta_0\approx \gamma_0\approx \delta_0 \approx\epsilon_0\ll 1$, where $\beta_0$, $\gamma_0$, $\delta_0$, and $\epsilon_0$ are related to the thermal, poloidal-current, flow and gravitating energies normalized to the poloidal-magnetic-field energy, respectively, and (b) in the high-energy regime $\beta_0\approx \gamma_0\approx \delta_0 \approx\epsilon_0\gg 1$. It turns out that in the high-energy regime all four forces, pressure-gradient, toroidal-magnetic-field, inertial, and gravitating contribute equally to the formation of magnetic surfaces very extended and localized about the symmetry plane such that the resulting equilibria resemble the accretion disks in astrophysics.Comment: 12 pages, latex, to be published in Geophys. Astrophys. Fluid Dynamic

Gut acellular matrix for the in vitro study of Enteric Nervous System cells

Enteric nervous system (ENS) cells respond to the intestinal extracellular matrix (ECM) signals changing their proliferation rate, migration and differentiation. In this study, we explored in vitro the adaptive response of primary ENS cell cultures to the stimulation of gut acellular matrix (AM) defining the gene expression profile of neuronal functionality markers. Scanning electron microscopy was used to detect the acquisition of specific morphological features. Intestinal AM was prepared using an enzyme-detergent treatment. Primary rat enteric cells were isolated from the myenteric plexus of postnatal rats using an enzymatic method and seeded on intestinal AM in the presence of exogenous neurotrophic factors. The morphological properties and the expression of specific differentiation markers were evaluated by Scanning Electron Microscopy (SEM) and wholemount fluorescent staining. In order to verify the synergic activity of soluble factors and AM, the gene expression of neurotransmitter receptors was evaluated by qPCR in ENS cells cultured in SM conditions in the presence or not of AM. The development of interconnected ganglion-like structures and the expression of neurotransmitter receptors suggested that gut matrix engineered with ENS cells could be useful for medical applications of regenerative medicine or for the in vitro assessment of tridimensional culture system of ENS

Validation of a high performance liquid chromatographic method for quantitative determination of boldine in fluid extract of boldo

A simple and specific method was validated for quantification of boldine in fluid extract of boldo (Peumus boldus Mol.) using high-performance liquid chromatography. A reversed-phase C18 , Phenomenex® (150 x 4.6 mm, 4 µm) column was employed. The mobile phase consisted of 0.1 % trifluoroacetic acid and acetonitrile (78:22, v/v) at a flow rate of 0.8 mL/min. The column was maintained at 30 °C and the boldine peak detection was performed at a wavelength of 281 nm. The parameters used in the validation process were: linearity, specificity, precision, accuracy, limit of detection, limit of quantification and robustness. The validated method was selective and linear (r≥0.9991) for boldine concentration considering 5.0, 10.0, 15.0, 20.0 and 25.0 micro;g/mL. The recovery ranged from 90.93 % to 96.24 % and the limit of quantification was 2.41 micro;g/mL. The precision determined was reported as RSD (1.73 %). The method can be successfully applied to measure boldine concentrations in Boldo extract and be included in routine analysis of quality control.Colegio de Farmacéuticos de la Provincia de Buenos Aire

Validation of a high performance liquid chromatographic method for quantitative determination of boldine in fluid extract of boldo

A simple and specific method was validated for quantification of boldine in fluid extract of boldo (Peumus boldus Mol.) using high-performance liquid chromatography. A reversed-phase C18 , Phenomenex® (150 x 4.6 mm, 4 µm) column was employed. The mobile phase consisted of 0.1 % trifluoroacetic acid and acetonitrile (78:22, v/v) at a flow rate of 0.8 mL/min. The column was maintained at 30 °C and the boldine peak detection was performed at a wavelength of 281 nm. The parameters used in the validation process were: linearity, specificity, precision, accuracy, limit of detection, limit of quantification and robustness. The validated method was selective and linear (r≥0.9991) for boldine concentration considering 5.0, 10.0, 15.0, 20.0 and 25.0 micro;g/mL. The recovery ranged from 90.93 % to 96.24 % and the limit of quantification was 2.41 micro;g/mL. The precision determined was reported as RSD (1.73 %). The method can be successfully applied to measure boldine concentrations in Boldo extract and be included in routine analysis of quality control.Colegio de Farmacéuticos de la Provincia de Buenos Aire

Heavy Flavour Production in Two-Photon Collisions

We review the production of charm and bottom quarks in two-photon collisions at e+e- colliders. The next-to-leading order QCD predictions for total cross sections and differential distributions are compared with recent experimental results.Comment: 6 pages, 2 figures. Talk given at the UK Phenomenology Workshop on Collider Physics, Durham, England, 19-24 Sep 199

X-rays investigations for the characterization of two 17th century brass instruments from Nuremberg

A recent finding at the Castello Sforzesco in Milan of two brass natural horns from the end of the 17th century and assigned to the Haas family from Nuremberg brought to light new information about this class of objects. The instruments were heavily damaged, but their historical value was great. In this study, a multidisciplinary approach mainly based on non-invasive analytical techniques and including X-rays investigations (X-ray radiography, X-ray fluorescence and X-ray diffraction) was used. The present study was aimed at: i) pointing out the executive techniques for archaeometric purposes; ii) characterizing the morphological and the chemical features of materials; and iii) identifying and mapping the damages of the structure and the alterations of the surface