92 research outputs found
Study Of Spatial Biological Systems Using a Graphical User Interface
Proceedings of the Tenth International Conference on Human-Computer Interaction, Crete, Greece, 22-27 June 2003In this paper, we describe a Graphical User Interface (GUI) designed to manage large quantities of image data of a biological system. After setting the design requirements for the system, we developed an ecology quantification GUI that assists biologists in analysing data. We focus on the main features of the interface and we present the results and an evaluation of the system. Finally, we provide some directions for some future work
The Effect of a Linear Tuning between the Antigenic Stimulations of CD4(+) T Cells and CD4(+) Tregs
We study the equilibria of an Ordinary Differencial Equation (ODE) system where CD4+ effector or helper T cells and Regulatory T cells (Tregs) are present. T cells trigger an immune response in the presence of their specific antigen. Regulatory T cells (Tregs) play a role in limiting auto-immune diseases due to their immune-suppressive ability. Here, we present explicit exact formulas that give the relationship between the concentration of T cells, the concentration of Tregs, and the antigenic stimulation of T cells, when the system is at equilibria, stable or unstable. We found a parameter region of bistability, limited by two thresholds of antigenic stimulation of T cells (hysteresis). Moreover, there are values of the slope parameter of the tuning for which an isola-center bifurcation appears, and, for some other values, there is a transcritical bifurcation. We also present time evolutions of the ODE system
Solar powered biohydrogen production requires specific localization of the hydrogenase
This work was supported by BBSRC Grant (BB/G021856/1) to SJB, PJN and CWM. We acknowledge support from the U.S. DoE, Biological and Environmental Research Program to MB, the U.S. DoE Fuel Cell Technologies Office (contract number DE-AC36-08-GO28308) to CAE and EPSRC (EP/F00270X/1) to MB and PJN
Supersymmetry Flows, Semi-Symmetric Space Sine-Gordon Models And The Pohlmeyer Reduction
We study the extended supersymmetric integrable hierarchy underlying the
Pohlmeyer reduction of superstring sigma models on semi-symmetric superspaces
F/G. This integrable hierarchy is constructed by coupling two copies of the
homogeneous integrable hierarchy associated to the loop Lie superalgebra
extension f of the Lie superalgebra f of F and this is done by means of the
algebraic dressing technique and a Riemann-Hilbert factorization problem. By
using the Drinfeld-Sokolov procedure we construct explicitly, a set of 2D spin
\pm1/2 conserved supercharges generating supersymmetry flows in the phase space
of the reduced model. We introduce the bi-Hamiltonian structure of the extended
homogeneous hierarchy and show that the two brackets are of the
Kostant-Kirillov type on the co-adjoint orbits defined by the light-cone Lax
operators L_\pm. By using the second symplectic structure, we show that these
supersymmetries are Hamiltonian flows, we compute part of the supercharge
algebra and find the supersymmetric field variations they induce. We also show
that this second Poisson structure coincides with the canonical
Lorentz-Invariant symplectic structure of the WZNW model involved in the
Lagrangian formulation of the extended integrable hierarchy, namely, the
semi-symmetric space sine-Gordon model (SSSSG), which is the Pohlmeyer reduced
action functional for the transverse degrees of freedom of superstring sigma
models on the cosets F/G. We work out in some detail the Pohlmeyer reduction of
the AdS_2xS^2 and the AdS_3xS^3 superstrings and show that the new conserved
supercharges can be related to the supercharges extracted from 2D superspace.
In particular, for the AdS_2xS^2 example, they are formally the same.Comment: V2: Two references added, V3: Modifications in section 2.6, V4:
Published versio
Localisation and interactions of the Vipp1 protein in cyanobacteria
Biotechnology and Biological Sciences Research Council. Grant Number: BB/G021856. Deutsche Forschungsgemeinschaft. Grant Number: FOR 929, SCHN 690/3-1. European Commission. Grant Number: FP7-PEOPLE-2009-IEF 254575. NFR. Grant Numbers: 192436, 197119. OCISB. Royal Society and Engineering and Physical Sciences Research Council. Grant Number: EP/G0061009/
The AdS(5)xS(5) Semi-Symmetric Space Sine-Gordon Theory
The generalized symmetric space sine-Gordon theories are a series of
1+1-integrable field theories that are classically equivalent to superstrings
on symmetric space spacetimes F/G. They are formulated in terms of a
semi-symmetric space as a gauged WZW model with fermions and a potential term
to deform it away from the conformal fixed point. We consider in particular the
case of PSU(2,2|4)/Sp(2,2)xSp(4) which corresponds to AdS(5)xS(5). We argue
that the infinite tower of conserved charges of these theories includes an
exotic N=(8,8) supersymmetry that is realized in a mildy non-local way at the
Lagrangian level. The supersymmetry is associated to a double central extension
of the superalgebra psu(2|2)+psu(2|2) and includes a non-trivial R symmetry
algebra corresponding to global gauge transformations, as well as 2-dimensional
spacetime translations. We then explicitly construct soliton solutions and show
that they carry an internal moduli superspace CP(2|1)xCP(2|1) with both bosonic
and Grassmann collective coordinates. We show how to semi-classical quantize
the solitons by writing an effective quantum mechanical system on the moduli
space which takes the form of a co-adjoint orbit of SU(2|2)xSU(2|2). The
spectrum consists of a tower of massive states in the short, or atypical,
symmetric representations, just as the giant magnon states of the string world
sheet theory, although here the tower is truncated.Comment: 39 pages, references adde
Fermionic Coset, Critical Level W^(2)_4-Algebra and Higher Spins
The fermionic coset is a limit of the pure spinor formulation of the AdS5xS5
sigma model as well as a limit of a nonlinear topological A-model, introduced
by Berkovits. We study the latter, especially its symmetries, and map them to
higher spin algebras.
We show the following. The linear A-model possesses affine
\AKMSA{pgl}{4}{4}_0 symmetry at critical level and its \AKMSA{psl}{4}{4}_0
current-current perturbation is the nonlinear model. We find that the
perturbation preserves -algebra symmetry at critical
level. There is a topological algebra associated to \AKMSA{pgl}{4}{4}_0 with
the properties that the perturbation is BRST-exact. Further, the
BRST-cohomology contains world-sheet supersymmetric symplectic fermions and the
non-trivial generators of the -algebra. The Zhu functor
maps the linear model to a higher spin theory. We analyze its
\SLSA{psl}{4}{4} action and find finite dimensional short multiplets.Comment: 25 page
Tunable kinetic proofreading in a model with molecular frustration
In complex systems, feedback loops can build intricate emergent phenomena, so
that a description of the whole system cannot be easily derived from the
properties of the individual parts. Here we propose that inter-molecular
frustration mechanisms can provide non trivial feedback loops which can develop
nontrivial specificity amplification. We show that this mechanism can be seen
as a more general form of a kinetic proofreading mechanism, with an interesting
new property, namely the ability to tune the specificity amplification by
changing the reactants concentrations. This contrasts with the classical
kinetic proofreading mechanism in which specificity is a function of only the
reaction rate constants involved in a chemical pathway. These results are also
interesting because they show that a wide class of frustration models exists
that share the same underlining kinetic proofreading mechanisms, with even
richer properties. These models can find applications in different areas such
as evolutionary biology, immunology and biochemistry
A Novel ZAP-70 Dependent FRET Based Biosensor Reveals Kinase Activity at both the Immunological Synapse and the Antisynapse
Many hypotheses attempting to explain the speed and sensitivity with which a T-cell discriminates the antigens it encounters include a notion of relative spatial and temporal control of particular biochemical steps involved in the process. An essential step in T-cell receptor (TCR) mediated signalling is the activation of the protein tyrosine kinase ZAP-70. ZAP-70 is recruited to the TCR upon receptor engagement and, once activated, is responsible for the phosphorylation of the protein adaptor, Linker for Activation of T-cells, or LAT. LAT phosphorylation results in the recruitment of a signalosome including PLCγ1, Grb2/SOS, GADS and SLP-76. In order to examine the real time spatial and temporal evolution of ZAP-70 activity following TCR engagement in the immune synapse, we have developed ROZA, a novel FRET-based biosensor whose function is dependent upon ZAP-70 activity. This new probe not only provides a measurement of the kinetics of ZAP-70 activity, but also reveals the subcellular localization of the activity as well. Unexpectedly, ZAP-70 dependent FRET was observed not only at the T-cell -APC interface, but also at the opposite pole of the cell or “antisynapse”
Kinesin expands and stabilizes the GDP-microtubule lattice
Kinesin-1 is a nanoscale molecular motor that walks towards the fast-growing (plus) ends of microtubules, hauling molecular cargo to specific reaction sites in cells. Kinesin-driven transport is central to the self-organization of eukaryotic cells and shows great promise as a tool for nano-engineering1. Recent work hints that kinesin may also play a role in modulating the stability of its microtubule track, both in vitro2,3 and in vivo4, but the results are conflicting5,6,7 and the mechanisms are unclear. Here, we report a new dimension to the kinesin–microtubule interaction, whereby strong-binding state (adenosine triphosphate (ATP)-bound and apo) kinesin-1 motor domains inhibit the shrinkage of guanosine diphosphate (GDP) microtubules by up to two orders of magnitude and expand their lattice spacing by ~1.6%. Our data reveal an unexpected mechanism by which the mechanochemical cycles of kinesin and tubulin interlock, and so allow motile kinesins to influence the structure, stability and mechanics of their microtubule track
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