Network Topology as a Driver of Bistability in the lac Operon

The lac operon in Escherichia coli has been studied extensively and is one of the earliest gene systems found to undergo both positive and negative control. The lac operon is known to exhibit bistability, in the sense that the operon is either induced or uninduced. Many dynamical models have been proposed to capture this phenomenon. While most are based on complex mathematical formulations, it has been suggested that for other gene systems network topology is sufficient to produce the desired dynamical behavior. We present a Boolean network as a discrete model for the lac operon. We include the two main glucose control mechanisms of catabolite repression and inducer exclusion in the model and show that it exhibits bistability. Further we present a reduced model which shows that lac mRNA and lactose form the core of the lac operon, and that this reduced model also exhibits the same dynamics. This work corroborates the claim that the key to dynamical properties is the topology of the network and signs of interactions.Comment: 15 pages, 13 figures, supplemental information include

Concentración de metanol en nafta reformulada con metanol como antidetonante

Los primeros antidetonantes utilizados en las naftas fueron el MMT y el plomo tetra etilo. Sin embargo, la emisión de plomo a la atmosfera genera serios problemas a la salud pública. Para la eventual eliminación de Plomo incremento el uso de otros componentes producidos en las refinerías por este proceso, tales como BTX. En la actualidad por estudios ambientales se comienza a utilizar alcoholes. En el presente trabajo se estudia el Metanol como antidetonante de una nafta reformulada. Por ello, se estudia el ELL del sistema ternario Metanol + Tolueno + Hexano. Los datos experimentales de líneas de unión del sistema ternario se obtuvieron a 278.15, 283.15, 288.15 y 293.15 K. Se graficaron los datos experimentales obteniéndose las curvas binodales para las distintas temperaturas. Los resultados experimentales muestran que la solubilidad aumenta conforme aumenta la temperatura.The first anti-detonating used in naphtha were MMT and tetra ethyl lead. Nevertheless, the emission of lead to the atmosphere generates serious problems to the public health. For the eventual elimination of Lead increased the use of other components produced in the refineries by this process, such as BTX. At the present time by environmental studies is begun to use alcohols. In the present work the methanol is studied like anti-detonating additive of reformulated naphtha. Therefore, the ELL of the ternary system Methanol + Toluene + Hexane is studied. The experimental data of ternary system tie lines were obtained at 278.15, 283.15, 288.15 and 293.15 K. The experimental data were plotted, obtaining the binodal curves for the different temperatures. The experimental results show that the solubility increases as the temperature increases.Fil: Veliz, Jonatán H.. Consejo Nacional de Investigaciones Científicas y TécnicasFil: Cases, Alicia M.. Consejo Nacional de Investigaciones Científicas y TécnicasFil: Gramajo, Monica B.. Consejo Nacional de Investigaciones Científicas y Técnica

Non-homogenous disks in the chain of matrices

We investigate the generating functions of multi-colored discrete disks with non-homogenous boundary conditions in the context of the Hermitian multi-matrix model where the matrices are coupled in an open chain. We show that the study of the spectral curve of the matrix model allows one to solve a set of loop equations to get a recursive formula computing mixed trace correlation functions to leading order in the large matrix limit.Comment: 25 pages, 4 figure

Ballast Treated with Asphalt Emulsion, Megarok and San Jose. AASTHO Standards

In the research work, the results obtained at the laboratory level of the lending material (ballast) treated with asphalt emulsion from the quarries "Megarok and San José" are compared, applying the AASTHO standards. The quarries are located in the Picoazá-La Sequita parish of the Portoviejo canton. Samples from both quarries were evaluated in the laboratory and it was possible to carry out tests of natural humidity, Atterberg, granulometric, compaction, and soil bearing capacity (CBR). Based on the results obtained, they were compared by disclosing which of the quarries meets the appropriate conditions within the construction standards and techniques, in order to stabilize the material with asphalt emulsion; in addition to comparing it with the specifications of the AASTHO standards and the MTOP standard. The result was that the materials extracted from the quarries do not meet the technical specifications; but when mixed with the asphalt emulsion, the Megarok material fulfills as type A base

Species-speciWc defense strategies of vegetative versus reproductive blades of the PaciWc kelps Lessonia nigrescens and Macrocystis integrifolia

Chemical defense is assumed to be costly and therefore algae should allocate defense investments in a way to reduce costs and optimize their overall fitness. Thus, lifetime expectation of particular tissues and their contribution to the fitness of the alga may affect defense allocation. Two brown algae common to the SE Pacific coasts, Lessonia nigrescens Bory and Macrocystis integrifolia Bory, feature important ontogenetic differences in the development of reproductive structures; in L. nigrescens blade tissues pass from a vegetative stage to a reproductive stage, while in M. integrifolia reproductive and vegetative functions are spatially separated on different blades. We hypothesized that vegetative blades of L. nigrescens with important future functions are more (or equally) defended than reproductive blades, whereas in M. integrifolia defense should be mainly allocated to reproductive blades (sporophylls), which are considered to make a higher contribution to fitness. Herein, within-plant variation in susceptibility of reproductive and vegetative tissues to herbivory and in allocation of phlorotannins (phenolics) and N-compounds was compared. The results show that phlorotannin and N-concentrations were higher in reproductive blade tissues for both investigated algae. However, preferences by amphipod grazers (Parhyalella penai) for either tissue type differed between the two algal species. Fresh reproductive tissue of L. nigrescens was more consumed than vegetative tissue, while the reverse was found in M. integrifolia, thus confirming the original hypothesis. This suggests that future fitness function might indeed be a useful predictor of anti-herbivore defense in large, perennial kelps. Results from feeding assays with artificial pellets that were made with air-dried material and extract-treated Ulva powder indicated that defenses in live algae are probably not based on chemicals that can be extracted or remain intact after air-drying and grinding up algal tissues. Instead, anti-herbivore defense against amphipod mesograzers seems to depend on structural traits of living algae

Negotiated matter: a robotic exploration of craft-driven innovation

This paper introduces a novel approach to craft-driven robotic innovation in architectural research. Here craft is not portrayed as a source of ornamental or historical inspiration, but instead as an open-ended process described by a framework involving material properties, diverging modes of knowledge production and representation, emergent tectonic configurations and embodied interaction with technology. To do so, this paper firstly contrasts a definition of craft (Pye 1968) with practices of robotic architectural production. Additionally, the notion of emergent tectonics resulting from negotiated material and technological processes is addressed by critically situating the theories of architectural tectonics by Kenneth Frampton (2001) and digital tectonics by Leach, Turnbull and Williams (2004) in the context of robotic fabrication in architecture. Finally, the ongoing project “Computing Craft” is presented as a case study illustrating a proposed framework for robotic craft-driven innovation

High proportion of cactus species threatened with extinction

This is the author accepted manuscript. The final version is available from Nature Publishing Group via the DOI in this record.Consejo Nacional de Ciencia y Tecnologí