2,785 research outputs found
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 dâun peuplement forestier en zone semi-dĂ©cidue de CĂŽte dâIvoire
Le dispositif permanent de la TĂ©nĂ© (CĂŽte dâIvoire) est un peuplement forestier amĂ©nagĂ© depuis 1978 afin dâĂ©tudier, Ă long terme, la dynamique des essences Ă potentiel commercial. En 1983, le dispositif a Ă©tĂ© parcouru Ă plus de 65% par un feu de forĂȘt. Lâobjectif de la prĂ©sente Ă©tude est de dĂ©crire lâeffet de la perturbation occasionnĂ©e par les interventions sylvicoles et le passage du feu sur la dynamique du peuplement. Les rĂ©sultats obtenus et les tests statistiques appliquĂ©s ont montrĂ© une homogĂ©nĂ©itĂ© entre les parcelles avant les modalitĂ©s sylvicoles tandis quâaprĂšs celle-ci une diffĂ©rence significative est observĂ©e entre les parcelles tĂ©moins et traitĂ©es. LâĂ©volution de la surface terriĂšre, au cours du temps, montre deux grandes pĂ©riodes dont la premiĂšre situĂ©e entre 1978 Ă 1982 correspond Ă lâeffet traitement et la seconde traduit par lâeffet du feu aprĂšs 1986. Lâimpact de la perturbation sâest fait aussi sentir en 1978 sur la surface terriĂšre des essences commerciales tandis quâau delĂ de 1994, cet effet sâest fait au profit des essences secondaires. Ces rĂ©sultats montrent que les interventions sylvicoles supposĂ©es favoriser lâaccroissement, en volume, des essences commerciales peuvent ĂȘtre vulnĂ©rables au feu et entraĂźner Ă long terme des effets majeurs sur la dynamique du peuplement.Mots clĂ©s : exploitation forestiĂšre, Ă©claircie, feu de forĂȘt, 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
accompanied by 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 productions via gluon-gluon
collision are in the order of 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
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
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