Assessment of the environmental and economic performance of agroforestry along a European gradient

Poste

Harmonically confined, semiflexible polymer in a channel: response to a stretching force and spatial distribution of the endpoints

We consider an inextensible, semiflexible polymer or worm-like chain which is confined in the transverse direction by a parabolic potential and subject to a longitudinal force at the ends, so that the polymer is stretched out and backfolding is negligible. Simple analytic expressions for the partition function, valid in this regime, are obtained for chains of arbitrary length with a variety of boundary conditions at the ends. The spatial distribution of the end points or radial distribution function is also analyzed.Comment: 14 pages including figure

A comparison of the cognitive difficulties posed by SPARQL query constructs

This study investigated difficulties in the comprehension of SPARQL. In particular, it compared the declarative and navigational styles present in the language, and various operators used in SPARQL property paths. The study involved participants selecting possible answers given a SPARQL query and knowledgebase. In general, no significant differences were found in terms of the response time and accuracy with which participants could answer questions expressed in either a declarative or navigational form. However, UNION did take significantly longer to comprehend than both braces and verti- cal line in property paths; with braces being faster than vertical line. Inversion and negated property paths both proved difficult, with their combination being very difficult indeed. Questions involving MINUS were answered more accu- rately than those involving negation in property paths, in particular where pred- icates were inverted. Both involve negation, but the semantics are different. With the MINUS questions, negation and inversion can be considered separate- ly; with property paths, negation and inversion need to be considered together. Participants generally expressed a preference for data represented graphically, and this preference was significantly correlated with accuracy of comprehen- sion. Implications for the design and use of query languages are discussed

Nanoconfinement-enhanced conformational response of single DNA molecules to changes in ionic environment

We show that the ionic environment plays a critical role in determining the configurational properties of DNA confined in silica nanochannels. The extension of DNA in the nanochannels increases as the ionic strength is reduced, almost tripling over two decades in ionic strength for channels around 100x100 nm in dimension. Surprisingly, we find that the variation of the persistence length alone with ionic strength is not enough to explain our results. The effect is due mainly to increasing self-avoidance created by the reduced screening of electrostatic interactions at low ionic strength. To quantify the increase in self-avoidance, we introduce a new parameter into the de Gennes theory: an effective DNA width that gives the increase in the excluded volume due to electrostatic repulsion

Amplified stretch of bottlebrush-coated DNA in nanofluidic channels

The effect of a cationic-neutral diblock polypeptide on the conformation of single DNA molecules confined in rectangular nanochannels is investigated with fluorescence microscopy. An enhanced stretch along the channel is observed with increased binding of the cationic block of the polypeptide to DNA. A maximum stretch of 85% of the contour length can be achieved inside a channel with a cross-sectional diameter of 200 nm and at a 2-fold excess of polypeptide with respect to DNA charge. With site-specific fluorescence labelling, it is demonstrated that this maximum stretch is sufficient to map large-scale genomic organization. Monte Carlo computer simulation shows that the amplification of the stretch inside the nanochannels is owing to an increase in bending rigidity and thickness of bottlebrush-coated DNA. The persistence lengths and widths deduced from the nanochannel data agree with what has been estimated from the analysis of atomic force microscopy images of dried complexes on silica.Singapore-MIT Alliance for Research and TechnologyNational Science Foundation (U.S.

The pre-WDVV ring of physics and its topology

We show how a simplicial complex arising from the WDVV (Witten-Dijkgraaf-Verlinde-Verlinde) equations of string theory is the Whitehouse complex. Using discrete Morse theory, we give an elementary proof that the Whitehouse complex $\Delta_n$ is homotopy equivalent to a wedge of $(n-2)!$ spheres of dimension $n-4$. We also verify the Cohen-Macaulay property. Additionally, recurrences are given for the face enumeration of the complex and the Hilbert series of the associated pre-WDVV ring.Comment: 13 pages, 4 figures, 2 table

Structure-activity relationships of hierarchical three-dimensional electrodes with photosystem II for semi-artifcial photosynthesis

Semi-artificial photosynthesis integrates photosynthetic enzymes with artificial electronics, which is an emerging approach to reroute the natural photoelectrogenetic pathways for sustainable fuel and chemical synthesis. However, the reduced catalytic activity of enzymes in bioelectrodes limits the overall performance and further applications in fuel production. Here, we show new insights into factors that govern the photoelectrogenesis in a model system consisting of photosystem II and three-dimensional indium tin oxide and graphene electrodes. Fluorescence microscopy and in situ surface-sensitive infrared spectroscopy are employed to probe the enzyme distribution and penetration within electrode scaffolds of different structures, which is further correlated with protein film-photoelectrochemistry to establish relationships between the electrode structure and enzyme activity. We find that the hierarchical 1 structure of electrodes mainly affects the protein integration, but not the enzyme activity. Photoactivity is more limited by light intensity and electronic communication at the biointerface. This study provides guidelines for maximizing the performance of semi-artificial photosynthesis and also presents a set of methodologies to probe the photoactive biofilms in three-dimensional electrodes.CSC-Cambridge PhD Scholarship, EPSRC PhD studentship, Newton-Mosharafa Research Fellowship, ERC Consolidator Grant 'MatEnSAP

A Tool to Recover Scalar Time-Delay Systems from Experimental Time Series

We propose a method that is able to analyze chaotic time series, gained from exp erimental data. The method allows to identify scalar time-delay systems. If the dynamics of the system under investigation is governed by a scalar time-delay differential equation of the form $dy(t)/dt = h(y(t),y(t-\tau_0))$, the delay time $\tau_0$ and the functi on $h$ can be recovered. There are no restrictions to the dimensionality of the chaotic attractor. The method turns out to be insensitive to noise. We successfully apply the method to various time series taken from a computer experiment and two different electronic oscillators