Bacterial Microcolonies in Gel Beads for High-Throughput Screening of Libraries in Synthetic Biology.

Synthetic biologists increasingly rely on directed evolution to optimize engineered biological systems. Applying an appropriate screening or selection method for identifying the potentially rare library members with the desired properties is a crucial step for success in these experiments. Special challenges include substantial cell-to-cell variability and the requirement to check multiple states (e.g., being ON or OFF depending on the input). Here, we present a high-throughput screening method that addresses these challenges. First, we encapsulate single bacteria into microfluidic agarose gel beads. After incubation, they harbor monoclonal bacterial microcolonies (e.g., expressing a synthetic construct) and can be sorted according their fluorescence by fluorescence activated cell sorting (FACS). We determine enrichment rates and demonstrate that we can measure the average fluorescent signals of microcolonies containing phenotypically heterogeneous cells, obviating the problem of cell-to-cell variability. Finally, we apply this method to sort a pBAD promoter library at ON and OFF states

Engineering synthetic spatial patterns in microbial populations and communities.

Spatial pattern formation is an important feature of almost all biological systems. Thanks to the advances in synthetic biology, we can engineer microbial populations and communities to display sophisticated spatial patterns. This bottom-up approach can be used to elucidate the general principles underlying pattern formation. Moreover, it is of interest for a plethora of applications, from the production of novel living materials to medical diagnostics. In this short review, we comment on the recent experimental advances in engineering the spatial patterns formed by microbes. We classify the synthetic patterns based on the input signals provided and the biological processes deployed. We highlight some applications of microbial pattern formation and discuss the challenges and potential future directions

Controlling spatiotemporal pattern formation in a concentration gradient with a synthetic toggle switch.

The formation of spatiotemporal patterns of gene expression is frequently guided by gradients of diffusible signaling molecules. The toggle switch subnetwork, composed of two cross-repressing transcription factors, is a common component of gene regulatory networks in charge of patterning, converting the continuous information provided by the gradient into discrete abutting stripes of gene expression. We present a synthetic biology framework to understand and characterize the spatiotemporal patterning properties of the toggle switch. To this end, we built a synthetic toggle switch controllable by diffusible molecules in Escherichia coli. We analyzed the patterning capabilities of the circuit by combining quantitative measurements with a mathematical reconstruction of the underlying dynamical system. The toggle switch can produce robust patterns with sharp boundaries, governed by bistability and hysteresis. We further demonstrate how the hysteresis, position, timing, and precision of the boundary can be controlled, highlighting the dynamical flexibility of the circuit

Impact de la perturbation par les interventions sylvicoles et le feu sur la dynamique d’un peuplement forestier en zone semi-décidue de Côte d’Ivoire

Le dispositif permanent de la Téné (Côte d’Ivoire) est un peuplement forestier aménagé depuis 1978 afin d’étudier, à long terme, la dynamique des essences à potentiel commercial. En 1983, le dispositif a été parcouru à plus de 65% par un feu de forêt. L’objectif de la présente étude est de décrire l’effet de la perturbation occasionnée par les interventions sylvicoles et le passage du feu sur la dynamique du peuplement. Les résultats obtenus et les tests statistiques appliqués ont montré une homogénéité entre les parcelles avant les modalités sylvicoles tandis qu’après celle-ci une différence significative est observée entre les parcelles témoins et traitées. L’évolution de la surface terrière, au cours du temps, montre deux grandes périodes dont la première située entre 1978 à 1982 correspond à l’effet traitement et la seconde traduit par l’effet du feu après 1986. L’impact de la perturbation s’est fait aussi sentir en 1978 sur la surface terrière des essences commerciales tandis qu’au delà de 1994, cet effet s’est fait au profit des essences secondaires. Ces résultats montrent que les interventions sylvicoles supposées favoriser l’accroissement, en volume, des essences commerciales peuvent être vulnérables au feu et entraîner à long terme des effets majeurs sur la dynamique du peuplement.Mots clés : exploitation forestière, éclaircie, feu de forêt, traitements sylvicoles, composition floristique

Cleaved surface of i-AlPdMn quasicrystals: Influence of the local temperature elevation at the crack tip on the fracture surface roughness

Roughness of i-AlPdMn cleaved surfaces are presently analysed. From the atomic scale to 2-3 nm, they are shown to exhibit scaling properties hiding the cluster (0.45 nm) aperiodic structure. These properties are quantitatively similar to those observed on various disordered materials, albeit on other ranges of length scales. These properties are interpreted as the signature of damage mechanisms occurring within a 2-3 nm wide zone at the crack tip. The size of this process zone finds its origin in the local temperature elevation at the crack tip. For the very first time, this effect is reported to be responsible for a transition from a perfectly brittle behavior to a nanoductile one.Comment: 8 page

Single chargino production via gluon-gluon fusion in a supersymmetric theory with an explicit R-parity violation

We studied the production of single chargino$\tilde{\chi}_1^{\pm}$ accompanied by $\mu^{\mp}$ lepton via gluon-gluon fusion at the LHC. The numerical analysis of their production rates is carried out in the mSUGRA scenario with some typical parameter sets. The results show that the cross sections of the $\tilde{\chi}_1^{\pm}\mu^{\mp}$ productions via gluon-gluon collision are in the order of $1 \sim 10^{2}$ femto barn quantitatively at the CERN LHC, and can be competitive with production mechanism via quark-antiquark annihilation process.Comment: LaTex file, 18 pages, 4 EPS file

Modeling combustion timing in an RCCI engine bymeans of a control oriented model

[EN] Reactivity controlled compression ignition (RCCI) engines as one of low temperature auto ignition combustion strategies have shown a good performance to reduce NO (x) and soot emission while increasing engine thermal efficiency. Combustion control of these types of engines is relatively complex because of their ignition type which makes it difficult to have a direct control on the start of the combustion. In this research, combustion phase of an RCCI engine was modeled with using a control-oriented method. The combustion properties such as start of the combustion, crank angle degree where 50 percent of the fuel is burnt(CA50) and the burn duration were modeled in this research. A modified knock integral model was used for start of combustion estimation. Using the effect of spontaneous front speed, burn duration was modeled where a mathematical model is developed; and Wiebe function is used to model CA50. Indicated mean effective pressure(IMEP) also estimated in this modeling. To validate the developed models, five experimental data sets from a heavy-duty RCCI engine were used. The results show the maximum mean errors of 1.7, 1.9 and 2.3 crank angle degree (CAD) for start of combustion, burn duration(BD) and the CA50, respectively and this quantity is 0.5 bar for IMEP in steady state condition. The transient condition of the engine operation was also investigated. The results and trends are promising in all characteristics of the combustion process especially in the modeling of the indicated mean effective pressure where the majority of the data have errors less than 1.5 bar.The authors acknowledge the support of Spanish Ministerio de Economia, Industria y Competitivad through project TRA2016-78717-R (AEI/FEDER, EU). Alvin Barbier participation was funded through grant ACIF/2018/141, Programa Operativo del Fondo Social Europeo (FSE) de la Comunitat Valenciana 2014-2020. Alireza Kakoee participation was funded through grants 43/3/298624 from Iran ministry of science, research and technology.Kakoee, A.; Bakhshan, Y.; Barbier, ARS.; Bares-Moreno, P.; Guardiola, C. (2020). Modeling combustion timing in an RCCI engine bymeans of a control oriented model. Control Engineering Practice. 97:1-15. https://doi.org/10.1016/j.conengprac.2020.1043211159

Hints of R-parity violation in B decays into τν\tau \nu

In this article we show that the recently observed enhanced semi-leptonic and leptonic decay rates of the B meson into \tau \nu modes can be explained within the frame work of R-parity violating (RPV) MSSM. In particular, RPV contributions involving the exchange of right-handed down-type squarks give a universal contribution to the B+ --> \tau \nu, B --> D \tau \nu and the B --> D* \tau \nu decays. We find that the masses and couplings that explain the enhanced B decay rates are phenomelogically viable and the squarks can possibly be observed at the LHC.Comment: 8 pages and 3 figures; Updated section 2 and 3, but results are unmodifie

A transverse current rectification in graphene superlattice

A model for energy spectrum of superlattice on the base of graphene placed on the striped dielectric substrate is proposed. A direct current component which appears in that structure perpendicularly to pulling electric field under the influence of elliptically polarized electromagnetic wave was derived. A transverse current density dependence on pulling field magnitude and on magnitude of component of elliptically polarized wave directed along the axis of a superlattice is analyzed.Comment: 12 pages, 6 figure